Intra-atrial pressure increases rate and organization of waves emanating from the superior pulmonary veins during atrial fibrillation.
AuthorsKalifa J, Jalife J, Zaitsev AV, Bagwe S, Warren M, Moreno J, Berenfeld O, Nattel S
JournalCirculation
PubMed ID12900337
'BACKGROUND: Atrial fibrillation (AF) commonly associates with atrial dilatation by poorly understood mechanisms. We hypothesized that elevation of intra-atrial pressure elicits high-frequency and spatio-temporally organized left atrial (LA) sources emanating from the superior pulmonary veins. METHODS AND RESULTS: We used a stretch-related AF model in the sheep heart to induce ... More
Odorant-specific spatial patterns in mucosal activity predict perceptual differences among odorants.
AuthorsKent PF, Youngentob SL, Sheehe PR
JournalJ Neurophysiol
PubMed ID8989412
'1. Using operant techniques, rats were trained to differentially report (i.e., identify) the odorants propanol, carvone, citral, propyl acetate, and ethylacetoacetate. After acquisition training, the animals were tested using a 5 x 5 confusion matrix design. The results of the behavioral tests were used to measure the degree of perceptual ... More
Ratiometric measurement of endothelial depolarization in arterioles with a potential-sensitive dye.
AuthorsBeach JM, McGahren ED, Xia J, Duling BR
JournalAm J Physiol
PubMed ID8764277
'A fluorescence ratio technique based on the voltage-sensitive dye 1-(3-sulfonatopropyl)-8-[beta-[2-di-n-butylamino)-6-naphythyl++ +]vinyl] pyridinium betaine (di-8-ANEPPS)has been developed for recording membrane potential changes during vascular responses of arterioles. Perfusion of hamster cheek pouch arterioles with the dye labeled the endothelial cell layer. voltage responses from the endothelium of intact arterioles were determined ... More
Fiber orientation and cell-cell coupling influence ventricular fibrillation dynamics.
AuthorsChoi BR, Liu T, Lavasani M, Salama G
JournalJ Cardiovasc Electrophysiol
PubMed ID12890049
'Cell Coupling Influences VF Dynamics. INTRODUCTION: The structure of ventricular fibrillation (VF) is influenced by regional differences in action potential durations and perhaps restitution kinetics and fiber anisotropy. The spatial organization of VF was investigated by measuring the cross-correlation (CC) and mutual information (MI) of membrane potential (Vm) oscillations recorded ... More
Optical recordings of the effect of electrical stimulation on action potential repolarization and the induction of reentry in two-dimensional perfused rabbit epicardium.
AuthorsKnisley SB, Hill BC
JournalCirculation
PubMed ID8222133
'BACKGROUND. Prolonged membrane depolarization induced by an electric shock in the heart may produce propagation block leading to repetitive beats. We studied prolonged depolarization and its role in repetitive beats in a thin epicardial layer of endocardially prefrozen arterially perfused rabbit heart. METHODS AND RESULTS. A laser scanner recorded optical ... More
The effect of asymmetric surface potentials on the intramembrane electric field measured with voltage-sensitive dyes.
AuthorsXu C, Loew LM
JournalBiophys J
PubMed ID12668484
'Ratiometric imaging of styryl potentiometric dyes can be used to measure the potential gradient inside the membrane (intramembrane potential), which is the sum of contributions from transmembrane potential, dipole potential, and the difference in the surface potentials at both sides of the membrane. Here changes in intramembrane potential of the ... More
Dye screening and signal-to-noise ratio for retrogradely transported voltage-sensitive dyes.
'Using a novel method for retrogradely labeling specific neuronal populations, we tested different styryl dyes in attempt to find dyes whose staining would be specific, rapid, and lead to large activity dependent signals. The dyes were injected into the ventral roots of the isolated chick spinal cord from embryos at ... More
Membrane potential induced by external electric field pulses can be followed with a potentiometric dye.
AuthorsEhrenberg B, Farkas DL, Fluhler EN, Lojewska Z, Loew LM
JournalBiophys J
PubMed ID3593876
'A potential-sensitive dye was recently used to measure the spatial variation in the membrane potential induced by an externally applied electric field. In this work, we demonstrate that the time course of these induced potentials can also be followed. Two experimental systems were explored. Dye fluorescence from HeLa cells could ... More
Errors caused by combination of Di-4 ANEPPS and Fluo3/4 for simultaneous measurements of transmembrane potentials and intracellular calcium.
AuthorsJohnson PL, Smith W, Baynham TC, Knisley SB
JournalAnn Biomed Eng
PubMed ID10468240
'Intracellular calcium concentration and transmembrane potentials are two important measurements used to study the mechanisms of cardiac activity. Fluorescent dyes have been used to measure these separately but not simultaneously in cardiac tissue. Fluo-3 and Fluo-4 (a recently improved version of Fluo-3) have been used to measure changes in intracellular ... More
Roles of electric field and fiber structure in cardiac electric stimulation.
AuthorsKnisley SB, Trayanova N, Aguel F
JournalBiophys J
PubMed ID10465752
'This study investigated roles of the variation of extracellular voltage gradient (VG) over space and cardiac fibers in production of transmembrane voltage changes (DeltaV(m)) during shocks. Eleven isolated rabbit hearts were arterially perfused with solution containing V(m)-sensitive fluorescent dye (di-4-ANEPPS). The epicardium received shocks from symmetrical or asymmetrical electrodes to ... More
Transmembrane voltage changes produced by real and virtual electrodes during monophasic defibrillation shock delivered by an implantable electrode.
AuthorsEfimov IR, Cheng YN, Biermann M, Van Wagoner DR, Mazgalev TN, Tchou PJ
JournalJ Cardiovasc Electrophysiol
PubMed ID9300301
'INTRODUCTION: Epicardial point stimulation produces nonuniform changes in the transmembrane voltage of surrounding cells with simultaneous occurrence of areas of transient positive and negative polarization. This is the phenomenon of virtual electrode. We sought to characterize the responses of epicardial ventricular tissue to the application of monophasic electric shocks from ... More
High-resolution nonlinear optical imaging of live cells by second harmonic generation.
AuthorsCampagnola PJ, Wei MD, Lewis A, Loew LM
JournalBiophys J
PubMed ID10585956
'By adapting a laser scanning microscope with a titanium sapphire femtosecond pulsed laser and transmission optics, we are able to produce live cell images based on the nonlinear optical phenomenon of second harmonic generation (SHG). Second harmonic imaging (SHIM) is an ideal method for probing membranes of living cells because ... More
Optical measurements of transmembrane potential changes during electric field stimulation of ventricular cells.
AuthorsKnisley SB, Blitchington TF, Hill BC, Grant AO, Smith WM, Pilkington TC, Ideker RE
JournalCirc Res
PubMed ID8418982
'We evaluated transmembrane potential changes at the ends of isolated rabbit ventricular myocytes during defibrillation-strength shocks given in the cellular refractory period. The myocytes were stimulated (S1 pulse) to produce an action potential. Then a constant-field shock (S2 pulse) with an electric field of 20 or 40 V/cm was given ... More
Optical multisite monitoring of cell excitation phenomena in isolated cardiomyocytes.
AuthorsWindisch H, Ahammer H, Schaffer P, Müller W, Platzer D
JournalPflugers Arch
PubMed ID7491277
'An especially designed setup which consists of an inverted fluorescence microscope, an argon ion laser and a photodiode array system permits membrane potential monitoring in isolated guinea-pig ventricular cardiomyocytes, stained with the voltage-sensitive dye di-4-ANEPPS, which responds linearly with relative fluorescence changes (delta F/F) approximately -8% per 100 mV. About ... More
Role of calcium cycling versus restitution in the mechanism of repolarization alternans.
AuthorsPruvot EJ, Katra RP, Rosenbaum DS, Laurita KR
JournalCirc Res
PubMed ID15016735
'T-wave alternans, a powerful marker of arrhythmic events, results from alternation in action potential duration (APD). The underlying cellular mechanism of APD alternans is unknown but has been attributed to either intracellular calcium (Ca2+) cycling or membrane ionic currents, manifested by a steep slope of cellular APD restitution. To address ... More
Voltage-sensitive dye recording of action potentials and synaptic potentials from sympathetic microcultures.
AuthorsChien CB, Pine J
JournalBiophys J
PubMed ID1681956
'Given the appropriate multicell electrophysiological techniques, small networks of cultured neurons (microcultures) are well suited to long-term studies of synaptic plasticity. To this end, we have developed an apparatus for optical recording from cultured vertebrate neurons using voltage-sensitive fluorescent dyes (Chien, C.-B., and J. Pine. 1991. J. Neurosci. Methods. 38:93-105). ... More
Preparation of giant liposomes in physiological conditions and their characterization under an optical microscope.
AuthorsAkashi K, Miyata H, Itoh H, Kinosita K
JournalBiophys J
PubMed ID8968594
'Unilamellar liposomes with diameters of 25-100 microns were prepared in various physiological salt solutions, e.g., 100 mM KCl plus 1 mM CaCl2. Successful preparation of the giant liposomes at high ionic strengths required the inclusion of 10-20% of a charged lipid, such as phosphatidylglycerol, phosphatidylserine, phosphatidic acid, or cardiolipin, in ... More
Characterization of shock-induced action potential extension during acute regional ischemia in rabbit hearts.
AuthorsKnisley SB, Holley LK
JournalJ Cardiovasc Electrophysiol
PubMed ID8542074
'INTRODUCTION: Defibrillation shocks produce extension of the myocardial action potential repolarization time (AP extension) in nonischemic myocardium. AP extension may synchronize repolarization in the heart because the extension increases when shock timing is increased. We tested whether AP extension occurs and whether it increases when shock timing is increased in ... More
Transmembrane voltage changes during unipolar stimulation of rabbit ventricle.
AuthorsKnisley SB
JournalCirc Res
PubMed ID7586236
'This study tested the prediction of bidomain models that unipolar stimulation of anisotropic myocardium produces transmembrane voltage changes (delta VmS) of opposite signs away from the electrode on perpendicular axes. Stimulation with a strength of 0.1 to 40 mA was applied from a point electrode on the left or right ... More
Presynaptic inhibition of primary olfactory afferents mediated by different mechanisms in lobster and turtle.
AuthorsWachowiak M, Cohen LB
JournalJ Neurosci
PubMed ID10516300
'Presynaptic regulation of transmission at the first olfactory synapse was investigated by selectively imaging axon terminals of receptor neurons in the lobster olfactory lobe and turtle olfactory bulb. In both species, action potential propagation into axon terminals after olfactory nerve stimulation was measured using voltage-sensitive dyes. In addition, in the ... More
A naphthyl analog of the aminostyryl pyridinium class of potentiometric membrane dyes shows consistent sensitivity in a variety of tissue, cell, and model membrane preparations.
'The fast potentiometric indicator di-4-ANEPPS is examined in four different preparations: lipid vesicles, red blood cells, squid giant axon, and guinea pig heart. The dye gives consistent potentiometric responses in each of these systems, although some of the detailed behavior varies. In lipid vesicles, the dye displays an increase in ... More
High-frequency network oscillations in cerebellar cortex.
AuthorsMiddleton SJ, Racca C, Cunningham MO, Traub RD, Monyer H, Knöpfel T, Schofield IS, Jenkins A, Whittington MA,
JournalNeuron
PubMed ID18549787
'Both cerebellum and neocortex receive input from the somatosensory system. Interaction between these regions has been proposed to underpin the correct selection and execution of motor commands, but it is not clear how such interactions occur. In neocortex, inputs give rise to population rhythms, providing a spatiotemporal coding strategy for ... More
Stationary and drifting spiral waves of excitation in isolated cardiac muscle.
'Excitable media can support spiral waves rotating around an organizing centre. Spiral waves have been discovered in different types of autocatalytic chemical reactions and in biological systems. The so-called ''re-entrant excitation'' of myocardial cells, causing the most dangerous cardiac arrhythmias, including ventricular tachycardia and fibrillation, could be the result of ... More
Voltage-imaging and simulation of effects of voltage- and agonist-activated conductances on soma-dendritic voltage coupling in cerebellar Purkinje cells.
AuthorsStaub C, De Schutter E, Knöpfel T
JournalJ Comput Neurosci
PubMed ID8792236
'We investigated the spread of membrane voltage changes from the soma into the dendrites of cerebellar Purkinje cells by using voltage-imaging techniques in combination with intracellular recordings and by performing computer simulations using a detailed compartmental model of a cerebellar Purkinje cell. Fluorescence signals from single Purkinje cells in cerebellar ... More
Quantifying spatial localization of optical mapping using Monte Carlo simulations.
AuthorsDing L, Splinter R, Knisley SB
JournalIEEE Trans Biomed Eng
PubMed ID11585033
'Optical mapping techniques used to study spatial distributions of cardiac activity can be divided into two categories. 1) Broad-field excitation method, in which hearts stained with voltage or calcium sensitive dyes are illuminated with broad-field excitation light and fluorescence is collected by image or photodiode arrays. 2) Laser scanning method, ... More
High-resolution fluorescent imaging does not reveal a distinct atrioventricular nodal anterior input channel (fast pathway) in the rabbit heart during sinus rhythm.
AuthorsEfimov IR, Fahy GJ, Cheng Y, Van Wagoner DR, Tchou PJ, Mazgalev TN
JournalJ Cardiovasc Electrophysiol
PubMed ID9083879
'INTRODUCTION: We sought to determine the precise pathways of engagement of the AV node during sinus rhythm. METHODS AND RESULTS: Langendorff-perfused rabbit hearts were stained with 20 microM of the voltage-sensitive dye di-4-ANEPPS. Preparations containing the right atrium, sinoatrial (SA) and AV nodes, and interatrial septum were subsequently dissected and ... More
Design and use of an "optrode" for optical recordings of cardiac action potentials.
AuthorsNeunlist M, Zou SZ, Tung L
JournalPflugers Arch
PubMed ID1614837
'An optical method was used to measure action potentials from frog ventricle, in vitro, under normal physiological conditions with 0.5-1 mM Ca2+ Ringer''s solution. The approach presented in this paper involves a portable fluorimeter coupled to a multimode optical fiber running into a glass pipette ("optrode") to carry both excitation ... More
Effects of heart isolation, voltage-sensitive dye, and electromechanical uncoupling agents on ventricular fibrillation.
AuthorsQin H, Kay MW, Chattipakorn N, Redden DT, Ideker RE, Rogers JM
JournalAm J Physiol Heart Circ Physiol
PubMed ID12679330
'We tested whether the interventions typically required for optical mapping affect activation patterns during ventricular fibrillation (VF). A 21 x 24 unipolar electrode array (1.5 mm spacing) was sutured to the left ventricular epicardium of 16 anesthetized pigs, and four episodes of electrically induced VF (30-s duration) were recorded. The ... More
Optical mapping technique applied to biventricular pacing: potential mechanisms of ventricular arrhythmias occurrence.
AuthorsGarrigue S, Reuter S, Efimov IR, Mazgalev TN, Jaïs P, Haïssaguerre M, Clementy J
JournalPacing Clin Electrophysiol
PubMed ID12687812
'Although it has been suggested that multisite ventricular pacing alleviates heart failure by restoring ventricular electrical synchronization, the respective roles of voltage output, interventricular delay, and pacing sites in the development of ventricular arrhythmias occurrence have not been studied during biventricular pacing or LV pacing. Voltage-sensitive dye was used in ... More
Validation of a voltage-sensitive dye (di-4-ANEPPS)-based method for assessing drug-induced delayed repolarisation in beagle dog left ventricular midmyocardial myocytes.
AuthorsHardy ME, Pollard CE, Small BG, Bridgland-Taylor M, Woods AJ, Valentin JP, Abi-Gerges N,
JournalJ Pharmacol Toxicol Methods
PubMed ID19414070
'INTRODUCTION: Evaluation of drug candidates in in-vitro assays of action potential duration (APD) is one component of preclinical safety assessment. Current assays are limited by technically-demanding, time-consuming electrophysiological methods. This study aimed to assess whether a voltage-sensitive dye-based assay could be used instead. METHODS: Optical APs were recorded using di-4-ANEPPS ... More
CCD imaging of the electrical activity in the leech nervous system.
AuthorsCanepari M, Campani M, Spadavecchia L, Torre V
JournalEur Biophys J
PubMed ID8765710
'A single ganglion of the nervous system of the leech Hirudo medicinalis was isolated. One or both roots emerging from each side of the ganglion were sucked into suction pipettes used either for extracellular stimulation or for recording the gross electrical activity. The ganglion was stained with the fluorescence voltage ... More
Diverse voltage-sensitive dyes modulate GABAA receptor function.
AuthorsMennerick S, Chisari M, Shu HJ, Taylor A, Vasek M, Eisenman LN, Zorumski CF,
JournalJ Neurosci
PubMed ID20181584
'Voltage-sensitive dyes are important tools for assessing network and single-cell excitability, but an untested premise in most cases is that the dyes do not interfere with the parameters (membrane potential, excitability) that they are designed to measure. We found that popular members of several different families of voltage-sensitive dyes modulate ... More
Virtual electrode effects in myocardial fibers.
AuthorsKnisley SB, Hill BC, Ideker RE
JournalBiophys J
PubMed ID8011903
'The changes in transmembrane potential during a stimulation pulse in the heart are not known. We have used transmembrane potential sensitive dye fluorescence to measure changes in transmembrane potential along fibers in an anisotropic arterially perfused rabbit epicardial layer. Cathodal or anodal extracellular point stimulation produced changes in transmembrane potential ... More
Virtual electrodes in cardiac tissue: a common mechanism for anodal and cathodal stimulation.
AuthorsWikswo JP, Lin SF, Abbas RA
JournalBiophys J
PubMed ID8599628
'Traditional cable analyses cannot explain complex patterns of excitation in cardiac tissue with unipolar, extracellular anodal, or cathodal stimuli. Epifluorescence imaging of the transmembrane potential during and after stimulation of both refractory and excitable tissue shows distinctive regions of simultaneous depolarization and hyperpolarization during stimulation that act as virtual cathodes ... More
Effects of bipolar point and line stimulation in anisotropic rabbit epicardium: assessment of the critical radius of curvature for longitudinal block.
AuthorsKnisley SB, Hill BC
JournalIEEE Trans Biomed Eng
PubMed ID8582725
'Excitation front shape and velocity were studied in anisotropic perfused rabbit epicardium stained with potentiometric fluorescent dye. In the combined results from all experiments, convex excitation fronts produced by stimulation with a single electrode propagated longitudinally 13.3% slower than flat excitation fronts produced by stimulation with a line of electrodes. ... More
Voltage-sensitive fluorescence of amphiphilic hemicyanine dyes in a black lipid membrane of glycerol monooleate.
AuthorsFromherz P, Schenk O
JournalBiochim Biophys Acta
PubMed ID8172915
'Amphiphilic fluorescent hemicyanine dyes were adsorbed to a hemispherical bimolecular membrane of glycerol monooleate. Their excitation spectra of fluorescence were as in water, their emission spectra were as in hydrocarbon. An AC-voltage was applied across the membrane and the relative changes of the spectra of excitation and of emission were ... More
High-speed imaging reveals neurophysiological links to behavior in an animal model of depression.
AuthorsAiran RD, Meltzer LA, Roy M, Gong Y, Chen H, Deisseroth K
JournalScience
PubMed ID17615305
'The hippocampus is one of several brain areas thought to play a central role in affective behaviors, but the underlying local network dynamics are not understood. We used quantitative voltage-sensitive dye imaging to probe hippocampal dynamics with millisecond resolution in brain slices after bidirectional modulation of affective state in rat ... More
A fluorometric approach to local electric field measurements in a voltage-gated ion channel.
AuthorsAsamoah OK, Wuskell JP, Loew LM, Bezanilla F
JournalNeuron
PubMed ID12526775
'Site-specific electrostatic measurements have been limited to soluble proteins purified for in vitro spectroscopic characterization or proteins of known structure; however, comparable measurements have not been made for functional membrane bound proteins. Here, using an electrochromic fluorophore, we describe a method to monitor localized electric field changes in a voltage-gated ... More
Optical recordings of ventricular excitability of frog heart by an extracellular stimulating point electrode.
AuthorsNeunlist M, Tung L
JournalPacing Clin Electrophysiol
PubMed ID7800567
'To enhance understanding of the excitability of cardiac muscle during rest, an optical technique using the fluorescent voltage sensitive dye di-4-ANEPPS was used. Unlike conventional electrical recordings, optical recordings are free from electrical artifacts and, therefore, allow the observation of the transmembrane potential not only following the stimulation pulse, but ... More
Spatially-resolved optical imaging of membrane potentials induced by applied electric fields.
AuthorsGross D, Loew LM, Ryan TA, Webb WW
JournalProg Clin Biol Res
PubMed ID3960915
Rapid measurement of toxicity using electrochromic dyes and frog embryos.
AuthorsStringer BK, Blankemeyer JT
JournalBull Environ Contam Toxicol
PubMed ID7691282
Fluorescent indicators of membrane potential: microspectrofluorometry and imaging.
AuthorsGross D, Loew LM
JournalMethods Cell Biol
PubMed ID2648110
Confocal microscopy of potentiometric fluorescent dyes.
AuthorsLoew LM
JournalMethods Cell Biol
PubMed ID8246781
Optical measurement of membrane potential in cells, organelles, and vesicles.
AuthorsFreedman JC, Novak TS
JournalMethods Enzymol
PubMed ID2747524
Cell membrane potential analysis.
AuthorsShapiro HM
JournalMethods Cell Biol
PubMed ID7532258
Optical imaging of cell membrane potential changes induced by applied electric fields.
AuthorsGross D, Loew LM, Webb WW
JournalBiophys J
PubMed ID3741986
We report the first imaging of the spatial distributions of transmembrane potential changes induced in nonexcitable cells by applied external electric fields. These changes are indicated by the fluorescence intensity of a charge-shift potentiometric dye incorporated in the cell plasma membrane and measured by digital intensified video microscopy. ... More
Voltage-sensitive dye imaging: Technique review and models.
AuthorsChemla S, Chavane F,
JournalJ Physiol Paris
PubMed ID19909809
In this review, we present the voltage-sensitive dye imaging (VSDI) method. The possibility offered for in vivo (and in vitro) brain imaging is unprecedented in terms of spatial and temporal resolution. However, the unresolved multi-component origin of the optical signal encourages us to perform a detailed analysis of the method ... More
Imaging membrane potential with voltage-sensitive dyes.
AuthorsZochowski M, Wachowiak M, Falk CX, Cohen LB, Lam YW, Antic S, Zecevic D
JournalBiol Bull
PubMed ID10707808
Membrane potential can be measured optically using a variety of molecular probes. These measurements can be useful in studying function at the level of an individual cell, for determining how groups of neurons generate a behavior, and for studying the correlated behavior of populations of neurons. Examples of the three ... More
Nonlinear optical properties of potential sensitive styryl dyes.
AuthorsHuang JY, Lewis A, Loew L
JournalBiophys J
PubMed ID3390517
The nonlinear optical properties of dyes that alter their optical characteristics rapidly with membrane potential are described. The second harmonic signals from these dyes characterized in this paper are among the largest that have been detected to date. Structural conclusions are drawn from the second harmonic signals generated by the ... More
Direct measurement of the voltage sensitivity of second-harmonic generation from a membrane dye in patch-clamped cells.
AuthorsMillard AC, Jin L, Lewis A, Loew LM
JournalOpt Lett
PubMed ID12885027
We report what is to our knowledge the first optical imaging of voltage-clamped cells by second-harmonic generation. For the membrane-staining styryl dye di-4-ANEPPS, we determined the sensitivity of second-harmonic generation to be 18%/100 mV at an excitation wavelength of 850 ns. This sensitivity is significantly better than the optimal 10%/100 ... More
Spectra of voltage-sensitive fluorescence of styryl-dye in neuron membrane.
AuthorsFromherz P, Lambacher A
JournalBiochim Biophys Acta
PubMed ID1911828
The voltage sensitivity of fluorescence of an aminobenzstyryl-pyridinium dye (di4-ANEPPS) is characterized in Retzius cells dissociated from the leech. The modulation of the complete spectra of excitation and emission is determined. The spectral changes induced by depolarization are described by a blue shift of the absorption spectrum, by a weaker ... More
Cholesterol-enriched lipid domains can be visualized by di-4-ANEPPDHQ with linear and nonlinear optics.
AuthorsJin L, Millard AC, Wuskell JP, Clark HA, Loew LM
JournalBiophys J
PubMed ID15879475
We present a membrane-staining dye, di-4-ANEPPDHQ, which differentiates liquid-ordered phases from liquid-disordered phases coexisting in model membranes under both linear and nonlinear microscopies. The dye's fluorescence emission spectrum is blue-shifted 60 nm in liquid-ordered phases compared with liquid-disordered phases, and shows strong second harmonic generation in the liquid-disordered phase compared ... More
Vortex shedding as a precursor of turbulent electrical activity in cardiac muscle.
In cardiac tissue, during partial blockade of the membrane sodium channels, or at high frequencies of excitation, inexcitable obstacles with sharp edges may destabilize the propagation of electrical excitation waves, causing the formation of self-sustained vortices and turbulent cardiac electrical activity. The formation of such vortices, which visually resembles vortex ... More
Monitoring biophysical properties of lipid membranes by environment-sensitive fluorescent probes.
AuthorsDemchenko AP, Mély Y, Duportail G, Klymchenko AS,
JournalBiophys J
PubMed ID19413953
We review the main trends in the development of fluorescence probes to obtain information about the structure, dynamics, and interactions in biomembranes. These probes are efficient for studying the microscopic analogs of viscosity, polarity, and hydration, as well as the molecular order, environment relaxation, and electrostatic potentials at the sites ... More
Probing membrane potential with nonlinear optics.
AuthorsBouevitch O, Lewis A, Pinevsky I, Wuskell JP, Loew LM
JournalBiophys J
PubMed ID8218895
The nonlinear optical phenomenon of second harmonic generation is shown to have intrinsic sensitivity to the voltage across a biological membrane. Our results demonstrate that this second order nonlinear optical process can be used to monitor membrane voltage with excellent signal to noise and other crucial advantages. These advantages suggest ... More
Voltage-sensitive dye recordings of electrophysiological activation in a Langendorff-perfused mouse heart.
AuthorsWitkowski FX, Clark RB, Larsen TS, Melnikov A, Giles WR
JournalCan J Cardiol
PubMed ID9413241
The pattern of electrophysiological activation of adult mouse ventricles was measured with the use of voltage-sensitive dye methods. Di-4-ANEPPS was used to monitor membrane potential as small changes in fluorescence, which were detected by a state of the art, cooled, charged coupled device camera/image intensifier system. The extremely rapid conduction ... More
Fast optical monitoring of microscopic excitation patterns in cardiac muscle.
AuthorsMüller W, Windisch H, Tritthart HA
JournalBiophys J
PubMed ID2790142
Many vital processes depend on the generation, changes, and conduction of cellular transmembrane potentials. Optical monitoring systems are well suited to detect such cellular electrical activities in networks of excitable cells and also tissues simultaneously at multiple sites. Here, an exceptionally fast array system (16 x 16 photodiodes, up to ... More
Three fluorescent probes for the flow-cytometric assessment of membrane potential in Saccharomyces cerevisiae.
AuthorsDenksteinová B, Sigler K, Plaásek J
JournalFolia Microbiol (Praha)
PubMed ID9449773
Three fluorescent probes, tetramethyl rhodamine ethyl ester (TMRE), 3,3'-dipropylthiacarbocyanine iodide (diS-C3(3)) and 3,3'-dipropyloxacarbocyanine iodide (diO-C3(3)), were tested for their suitability as fluorescent indicators of membrane potential in Saccharomyces cerevisiae in studies performed by flow cytometry. For all these dyes the intensity of fluorescence of stained cells increased with probe concentration ... More
Identification of neural circuits by imaging coherent electrical activity with FRET-based dyes.
AuthorsCacciatore TW, Brodfuehrer PD, Gonzalez JE, Jiang T, Adams SR, Tsien RY, Kristan WB, Kleinfeld D
JournalNeuron
PubMed ID10433258
We show that neurons that underlie rhythmic patterns of electrical output may be identified by optical imaging and frequency-domain analysis. Our contrast agent is a two-component dye system in which changes in membrane potential modulate the relative emission between a pair of fluorophores. We demonstrate our methods with the circuit ... More
In vitro electrophysiological mapping of stem cells.
AuthorsWeinberg S, Lipke EA, Tung L,
JournalMethods Mol Biol
PubMed ID20680822
The use of stem cells for cardiac regeneration is a revolutionary, emerging research area. For proper function as replacement tissue, stem cell-derived cardiomyocytes (SC-CMs) must electrically couple with the host cardiac tissue. Electrophysiological mapping techniques, including microelectrode array (MEA) and optical mapping, have been developed to study cardiomyocytes and cardiac ... More
Wide-field and two-photon imaging of brain activity with voltage- and calcium-sensitive dyes.
AuthorsHomma R, Baker BJ, Jin L, Garaschuk O, Konnerth A, Cohen LB, Bleau CX, Canepari M, Djurisic M, Zecevic D,
JournalMethods Mol Biol
PubMed ID18839087
This chapter presents three examples of imaging brain activity with voltage- or calcium-sensitive dyes. Because experimental measurements are limited by low sensitivity, the chapter then discusses the methodological aspects that are critical for optimal signal-to-noise ratio. Two of the examples use wide-field (1-photon) imaging and the third uses two-photon scanning ... More
Anatomical and functional imaging of neurons using 2-photon laser scanning microscopy.
AuthorsDenk W, Delaney KR, Gelperin A, Kleinfeld D, Strowbridge BW, Tank DW, Yuste R
JournalJ Neurosci Methods
PubMed ID7869748
Light scattering by brain tissue and phototoxicity are major obstacles to the use of high-resolution optical imaging and photo-activation ('uncaging') of bioactive compounds from inactive ('caged') precursors in intact and semi-intact nervous systems. Optical methods based on 2-photon excitation promise to reduce these obstacles (Denk, 1994; Denk et al., 1990, ... More
Analysis of the effect of medium and membrane conductance on the amplitude and kinetics of membrane potentials induced by externally applied electric fields.
AuthorsLojewska Z, Farkas DL, Ehrenberg B, Loew LM
JournalBiophys J
PubMed ID2752081
The kinetics and amplitudes of membrane potential induced by externally applied electric field pulses are determined for a spherical lipid bilayer using a voltage-sensitive dye. Several experimental parameters were systematically varied. These included the incorporation of gramicidin into the membrane to alter its conductivity and the variation of the external ... More
Di-4-ANEPPS causes photodynamic damage to isolated cardiomyocytes.
AuthorsSchaffer P, Ahammer H, Müller W, Koidl B, Windisch H
JournalPflugers Arch
PubMed ID8052525
Action potential recordings from isolated guinea pig ventricular cells in the whole-cell recording mode were used to study the toxic and photodynamic properties of the voltage-sensitive fluorescent dye di-4-ANEPPS. Staining of the cardiomyocytes with di-4-ANEPPS (30 or 60 microM; 10 min) did not alter the action potential shape. When the ... More
Intramural multisite recording of transmembrane potential in the heart.
AuthorsHooks DA, LeGrice IJ, Harvey JD, Smaill BH
JournalBiophys J
PubMed ID11606280
Heart surface optical mapping of transmembrane potentials has been widely used in studies of normal and pathological heart rhythms and defibrillation. In these studies, three-dimensional spatio-temporal events can only be inferred from two-dimensional surface potential maps. We present a novel optical system that enables high fidelity transmural recording of transmembrane ... More
Spectra, membrane binding, and potentiometric responses of new charge shift probes.
AuthorsFluhler E, Burnham VG, Loew LM
JournalBiochemistry
PubMed ID4084490
The properties of a series of new potentiometric membrane probes have been explored. The probes all contain an (aminostyryl)pyridinium chromophore or a more highly conjugated analogue. The spectral properties of the dyes are discussed in terms of the excitation-induced charge shift from the pyridine to the aniline; this charge shift ... More
Dual-wavelength ratiometric fluorescence measurements of membrane potential.
AuthorsMontana V, Farkas DL, Loew LM
JournalBiochemistry
PubMed ID2765500
This work shows that the voltage across membranes in two very different preparations, lipid vesicles in suspension and individual HeLa cells under a microscope, is linearly related to the ratio of fluorescence excited from the two wings of the absorption spectrum of a voltage-sensitive dye. The dye di-4-ANEPPS [1-(3-sulfonatopropyl)-4-[beta-[2-(di-n-butylamino)-6-naphthyl] vin ... More
Effects of elevated extracellular potassium on the stimulation mechanism of diastolic cardiac tissue.
AuthorsSidorov VY, Woods MC, Wikswo JP
JournalBiophys J
PubMed ID12719272
During cardiac disturbances such as ischemia and hyperkalemia, the extracellular potassium ion concentration is elevated. This in turn changes the resting transmembrane potential and affects the excitability of cardiac tissue. To test the hypothesis that extracellular potassium elevation also alters the stimulation mechanism, we used optical fluorescence imaging to examine ... More
Voltage-sensitive fluorescence of amphiphilic hemicyanine dyes in neuron membrane.
AuthorsFromherz P, Müller CO
JournalBiochim Biophys Acta
PubMed ID8347665
Fluorescent amphiphilic hemicyanine dyes were adsorbed to the plasma membrane of isolated Retzius neurons of the leech. Voltage steps were applied to the neuron by the patch-clamp technique in whole-cell configuration. The change of fluorescence was observed as induced by the voltage jump. The relative changes of the excitation spectrum ... More
Optical imaging of the heart.
AuthorsEfimov IR, Nikolski VP, Salama G
JournalCirc Res
PubMed ID15242982
Optical techniques have revolutionized the investigation of cardiac cellular physiology and advanced our understanding of basic mechanisms of electrical activity, calcium homeostasis, and metabolism. Although optical methods are widely accepted and have been at the forefront of scientific discoveries, they have been primarily applied at cellular and subcellular levels and ... More
Somatomotor and oculomotor inferior olivary neurons have distinct electrophysiological phenotypes.
AuthorsUrbano FJ, Simpson JI, Llinás RR
JournalProc Natl Acad Sci U S A
PubMed ID17050678
The electrophysiological properties of rat inferior olive (IO) neurons in the dorsal cap of Kooy (DCK) and the adjacent ventrolateral outgrowth (VLO) were compared with those of IO neurons in the principal olive (PO). Whereas DCK/VLO neurons are involved in eye movement control via their climbing fiber projection to the ... More
Measurement of membrane potential in Saccharomyces cerevisiae by the electrochromic probe di-4-ANEPPS: effect of intracellular probe distribution.
AuthorsChaloupka R, Plásek J, Slavík J, Siglerová V, Sigler K
JournalFolia Microbiol (Praha)
PubMed ID9438347
Changes in the membrane potential of Saccharomyces cerevisiae were monitored by the electrochromic probe 3-(4-(2-(6-(dibutylamino)-2-naphthyl)-trans- ethenyl)pyridinium)propanesulfonate (di-4-ANEPPS) that should incorporate into the plasma membrane. The probe had suitable spectral characteristics and exhibited an electrochromic shift upon a change in membrane potential but the magnitude of the response increased with time. ... More
Oxidative phosphorylation by ADP + P(i)-loaded membrane vesicles of alkaliphilic Bacillus firmus OF4.
AuthorsGuffanti AA, Krulwich TA
JournalJ Biol Chem
PubMed ID8063796
ATP synthesis in ADP + P(i)-loaded membrane vesicles of the facultative alkaliphile Bacillus firmus OF4 at an external pH of 10.5 did not depend upon the presence of cell wall polymers, e.g. as a proton barrier or sequestration device. Upon energization with ascorbate plus phenazine methosulfate, vesicles at pH(out) = ... More
Periodic current injection (PCI)--a new method to image steady-state membrane potential of single neurons in situ using extracellular voltage-sensitive dyes.
AuthorsBorst A
JournalZ Naturforsch [C]
PubMed ID7546036
A new method is described which allows to image the steady-state distribution of membrane potential of single neurons in situ. The method consists of staining the tissue with an extracellular voltage-sensitive dye (Di-4-ANEPPS) and impaling a single neuron with a microelectrode. After focusing the imaging system onto the cell a ... More
Functional study of the rat cortical microcircuitry with voltage-sensitive dye imaging of neocortical slices.
AuthorsYuste R, Tank DW, Kleinfeld D
JournalCereb Cortex
PubMed ID9276179
The computations performed within cortex are likely to be determined by its internal dynamics in addition to its pattern of afferent input. As a step toward characterizing these dynamics, we have imaged electrical activity in slices from rat primary visual cortex stained with the voltage-sensitive dye di-4-ANEPPS. In response to ... More
Surface-bound optical probes monitor protein translocation and surface potential changes during the bacteriorhodopsin photocycle.
AuthorsHeberle J, Dencher NA
JournalProc Natl Acad Sci U S A
PubMed ID1497755
Light-induced H+ release and reuptake as well as surface potential changes inherent in the bacterio-rhodopsin reaction cycle were measured between 10 degrees C and 50 degrees C. Signals of optical pH indicators covalently bound to Lys-129 at the extracellular surface of bacteriorhodopsin were compared with absorbance changes of probes residing ... More
Mapping action potentials and calcium transients simultaneously from the intact heart.
AuthorsLaurita KR, Singal A
JournalAm J Physiol Heart Circ Physiol
PubMed ID11299206
Intracellular calcium handling plays an important role in cardiac electrophysiology. Using two fluorescent indicators, we developed an optical mapping system that is capable of measuring calcium transients and action potentials at 256 recording sites simultaneously from the intact guinea pig heart. On the basis of in vitro measurements of dye ... More
Fluorescent probes for non-invasive bioenergetic studies of whole cyanobacterial cells.
AuthorsTeuber M, Rögner M, Berry S
JournalBiochim Biophys Acta
PubMed ID11418095
Fluorescent DeltapH and DeltaPsi indicators have been screened for the non-invasive monitoring of bioenergetic processes in whole cells of the cyanobacterium Synechocystis sp. PCC 6803. Acridine yellow and Acridine orange proved to be the best DeltapH indicators for the investigation of thylakoid and cytoplasmic membrane energization: While Acridine yellow indicated ... More
Optical detection of neuromodulatory effects of conditioned taste aversion in the pond snail Lymnaea stagnalis.
AuthorsKojima S, Hosono T, Fujito Y, Ito E
JournalJ Neurobiol
PubMed ID11598919
Multiple site optical recording was used to analyze the neural activity changes caused by conditioned taste aversion (CTA) training in the pond snail Lymnaea stagnalis. In response to electrical stimulation of the median lip nerve, which transmits chemosensory signals of appetitive taste to the central nervous system, we optically detected ... More
Spatiotemporal evolution of ventricular fibrillation.
AuthorsWitkowski FX, Leon LJ, Penkoske PA, Giles WR, Spano ML, Ditto WL, Winfree AT
JournalNature
PubMed ID9510250
Sudden cardiac death is the leading cause of death in the industrialized world, with the majority of such tragedies being due to ventricular fibrillation. Ventricular fibrillation is a frenzied and irregular disturbance of the heart rhythm that quickly renders the heart incapable of sustaining life. Rotors, electrophysiological structures that emit ... More
Comparative study on neural oscillation in the procerebrum of the terrestrial slugs Incilaria bilineata and
AuthorsKawahara S, Toda S, Suzuki Y, Watanabe S, Kirino Y
JournalJ Exp Biol
PubMed ID9319765
Coherent oscillatory activities in procerebral neurones have been described in Limax maximus; however, the electrical properties of the procerebrum of other terrestrial molluscs are less well understood. We have examined oscillatory activity in the procerebrum of Incilaria bilineata and Limax marginatus. The local field potential measured in the procerebrum of ... More
Two-photon excitation of di-4-ANEPPS for optical recording of action potentials in rabbit heart.
AuthorsDumas JH, Knisley SB, Kinisley SB
JournalAnn Biomed Eng
PubMed ID16389528
Cardiac action potentials have been measured with single-photon excitation (SPE) of transmembrane voltage-sensitive fluorescent dye. Two-photon excitation (TPE) may have advantages for localization and depth of the tissue region from which the action potential is measured. However measurements of action potentials with SPE have not been demonstrated. We sought to ... More
Quantification of optical signals with electrophysiological signals in neural activities of Di-4-ANEPPS stained rat hippocampal slices.
AuthorsTominaga T, Tominaga Y, Yamada H, Matsumoto G, Ichikawa M
JournalJ Neurosci Methods
PubMed ID11000407
We have quantified the optical signals of synaptically induced neural activities in an in vitro brain slice preparation in terms of electrophysiological signals. The qualification was done using electrophysiologically well known neural activities in the CA1 area of rat hippocampal slices stained with externally applied fluorescent voltage-sensitive dye (VSD; Di-4-ANEPPS). ... More
Nonlinear effects in subthreshold virtual electrode polarization.
AuthorsSambelashvili AT, Nikolski VP, Efimov IR
JournalAm J Physiol Heart Circ Physiol
PubMed ID12742834
Introduction of the virtual electrode polarization (VEP) theory suggested solutions to several century-old puzzles of heart electrophysiology including explanation of the mechanisms of stimulation and defibrillation. Bidomain theory predicts that VEPs should exist at any stimulus strength. Although the presence of VEPs for strong suprathreshold pulses has been well documented, ... More
Enhancement of odorant-induced mucosal activity patterns in rats trained on an odorant identification task.
AuthorsYoungentob SL, Kent PF
JournalBrain Res
PubMed ID7719728
Previous studies have demonstrated that there are intrinsic spatial patterns of odorant sensitivity across the rat olfactory mucosa. The question of how these patterns are determined and whether they are modifiable with experience remains open. Therefore, the present study examined whether the odorant-induced spatial activity patterns which are characteristic of ... More
Developmental toxicology of solamargine and solasonine glycoalkaloids in frog embryos.
AuthorsBlankemeyer JT, McWilliams ML, Rayburn JR, Weissenberg M, Friedman M
JournalFood Chem Toxicol
PubMed ID9662413
As part of an effort to improve the safety of plant foods, a need exists to define the relative toxicities of structurally different glycoalkaloids and metabolites which may be present in Solanum plant species such as potatoes, tomatoes and eggplants. The objectives of this study were to determine the relative ... More
Total internal reflection fluorescence and electrocapillary investigations of adsorption at a H2O-dichloroethane electrochemical interface. 1. Low-frequency behavior
AuthorsJones MA, Bohn PW
JournalAnal Chem
PubMed ID10959963
Total internal reflection fluorescence and electrocapillary measurements are employed to provide complementary potential-dependent information about the mechanical and photophysical properties of the interface between two immiscible electrolyte solutions, 1,2-dichloroethane-H2O. Adsorption of the zwitterionic amphiphile, di-N-butylaminonaphthylethenylpyridiniumpropylsulfonate (I) produces an interface with mechanical (interfacial tension) and charge transport properties qualitatively like the ... More
Voltage-sensitive dye mapping in Langendorff-perfused rat hearts.
AuthorsNygren A, Kondo C, Clark RB, Giles WR
JournalAm J Physiol Heart Circ Physiol
PubMed ID12424095
An imaging system suitable for recordings from Langendorff-perfused rat hearts using the voltage-sensitive dye 4-[beta-[2-(di-n-butylamino)-6-naphthyl]vinyl]pyridinium (di-4-ANEPPS) has been developed. Conduction velocity was measured under hyper- and hypokalemic conditions, as well as at physiological and reduced temperature. Elevation of extracellular [K(+)] to 9 mM from 5.9 mM caused a slowing of ... More
Effects of cardiac work on electrical potential gradient across mitochondrial membrane in perfused rat hearts.
The myocardium responds to alterations in cardiac work by changing its rate of O2 consumption. This reflects an increase in the oxidative synthesis of ATP to meet the contractile demand for ATP. However, the biochemical mechanisms responsible for increased ATP synthesis are not fully understood. To localize the flux-controlling reaction(s) ... More
Overexpression of the cystic fibrosis transmembrane conductance regulator in NIH 3T3 cells lowers membrane potential and intracellular pH and confers a multidrug resistance phenotype.
AuthorsWei LY, Stutts MJ, Hoffman MM, Roepe PD
JournalBiophys J
PubMed ID8519988
Because of the similarities between the cystic fibrosis transmembrane conductance regulator (CFTR) and multidrug resistance (MDR) proteins, recent observations of decreased plasma membrane electrical potential (delta psi) in cells overexpressing either MDR protein or the CFTR, and the effects of delta psi on passive diffusion of chemotherapeutic drugs, we have ... More
Asymmetric pore distribution and loss of membrane lipid in electroporated DOPC vesicles.
AuthorsTekle E, Astumian RD, Friauf WA, Chock PB
JournalBiophys J
PubMed ID11463638
An externally applied electric field across vesicles leads to transient perforation of the membrane. The distribution and lifetime of these pores was examined using 1,2-di-oleoyl-sn-glycero-3-phosphocholine (DOPC) phospholipid vesicles using a standard fluorescent microscope. The vesicle membrane was stained with a fluorescent membrane dye, and upon field application, a single membrane ... More
Fluorescent styryl dyes as probes for Na,K-ATPase reaction mechanism: significance of the charge of the hydrophilic moiety of RH dyes.
AuthorsFedosova NU, Cornelius F, Klodos I
JournalBiochemistry
PubMed ID8527456
The fluorescence responses of a series of potential-sensitive styryl-based dyes (either zwitterionic RH160, RH421, di-4-ANEPPS, or positively charged RH795, RH414, RH461) to phosphorylation of Na,K-ATPase from ATP or inorganic phosphate, and ouabain binding to phospho- or dephosphoforms, have been characterized and compared in broken membrane preparations of the enzyme. Zwitterionic ... More
A method of determining electrical potential gradient across mitochondrial membrane in perfused rat hearts.
The electrical potential gradient across the mitochondrial membrane (delta psi m) in perfused rat hearts was estimated by calculating the equilibrium distribution of the lipophilic cation tetraphenylphosphonium (TPP+), using measured kinetic constants of uptake and release of TPP+. First-order rate constants of TPP+ uptake were measured during 30-min perfusions of ... More
Membrane depolarization is the initial action of crotoxin on isolated murine skeletal muscle.
Although much is known about the pathogenesis of crotoxin-induced muscle damage, the initial site and action of the toxin is still not clear. In this study we used an electrochromic fluorescent dye, Di-4-ANEPPS, to measure the changes in membrane potential of isolated murine omohyoid muscle to determine if depolarization could ... More
Wavebreak formation during ventricular fibrillation in the isolated, regionally ischemic pig heart.
AuthorsZaitsev AV, Guha PK, Sarmast F, Kolli A, Berenfeld O, Pertsov AM, de Groot JR, Coronel R, Jalife J
JournalCirc Res
PubMed ID12600877
Both fixed and dynamic heterogeneities were implicated in the mechanism of wavebreak (WB) generation during ventricular fibrillation (VF). However, their relative roles remain unclear. We hypothesized that during ischemic VF, the WBs are produced primarily because of a fixed heterogeneity; namely, the gradient of refractoriness across the ischemic border zone ... More
The interaction of imposed and inherent olfactory mucosal activity patterns and their composite representation in a mammalian species using voltage-sensitive dyes.
AuthorsKent PF, Mozell MM, Murphy SJ, Hornung DE
JournalJ Neurosci
PubMed ID8613801
From amphibian data, two mechanisms that could underlie the encoding of odorants by the mucosal activity patterns they engender are as follows (1) receptors with similar odorant selectivities could be aggregated spatially on the mucosa (inherent patterns); (2) in analogy to gas chromatography, as odorants are drawn along the surface ... More
Line stimulation parallel to myofibers enhances regional uniformity of transmembrane voltage changes in rabbit hearts.
AuthorsKnisley SB, Baynham TC
JournalCirc Res
PubMed ID9242184
The sign of transmembrane voltage (Vm) change (delta Vm) in the heart during unipolar point stimulation is nonuniform, which introduces dispersion of states of Vm-dependent ion channels that depends on fiber orientation. We hypothesized that line stimulation parallel to cardiac fibers increases regional uniformity of the delta Vm sign. To ... More
Voltage-sensitive dyes: measurement of membrane potentials induced by DC and AC electric fields.
AuthorsLoew LM
JournalBioelectromagnetics
PubMed ID1285714
Dye indicators of membrane potential have been available for the past 15 years and have been employed in numerous studies of cell physiology. Since the cell membrane is a likely primary site for the cascade of events resulting in a biological response to electromagnetic fields, methodologies for monitoring the membrane ... More
Chronic inhibition of Na+/H+-exchanger attenuates cardiac hypertrophy and prevents cellular remodeling in heart failure.
AuthorsBaartscheer A, Schumacher CA, van Borren MM, Belterman CN, Coronel R, Opthof T, Fiolet JW
JournalCardiovasc Res
PubMed ID15621036
OBJECTIVE: In patients with heart disease, the transition from compensatory hypertrophy to heart failure (HF) is associated with altered calcium handling. Up-regulated Na(+)/H(+)-exchanger (NHE-1) activity underlies increased [Na(+)](i) and disturbance of cellular calcium handling in HF. We hypothesize that chronic inhibition of NHE-1 activity prevents the hypertrophic response, cellular remodeling, ... More
Spatial distribution of cardiac transmembrane potentials around an extracellular electrode: dependence on fiber orientation.
AuthorsNeunlist M, Tung L
JournalBiophys J
PubMed ID7647235
Recent theoretical models of cardiac electrical stimulation or defibrillation predict a complex spatial pattern of transmembrane potential (Vm) around a stimulating electrode, resulting from the formation of virtual electrodes of reversed polarity. The pattern of membrane polarization has been attributed to the anisotropic structure of the tissue. To verify such ... More