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PubMed1997

Learning-induced changes in rat piriform cortex activity mapped using multisite recording with voltage sensitive dye.

The piriform cortex (PCx) has a potential role in storage and recall of olfactory information. This study is a first extensive investigation of the spatiotemporal distribution of activity in the PCx induced by learned sensory inputs following conditioning. In a conditioned group, rats chronically implanted with four electrodes in the olfactory bulb were trained to associate the electrical stimulation of a given bulbar electrode with a positive reinforcement, while stimulation of a different electrode predicted a negative reinforcement. In a familiarized group, rats received the same protocol of daily electrical stimulation with no associated reinforcement. At the end of the conditioning or familiarization episode, activity evoked in the PCx was optically mapped using a 144 photodiode array. In the anaesthetized rats, PCx maps were recorded in response to stimulation of each of the four bulbar electrodes using either high (0.5-1 mA) or low (0.1 mA) test current intensities. Low intensity stimulation revealed that conditioning selectively enhanced the probability of occurrence of a signal composed of a single late (56-73 ms) component which occurred almost simultaneously on a large PCx area. In the conditioned group, high intensity stimulation through either of the four electrodes revealed a potentiation of the early (17-30 ms) disynaptic component of the PCx response in the most posterior part of the PCx as well as a homogeneous increase of the late (39-52 ms) component spread over the PCx areas. These data suggest that learning induces synaptic changes at different nodes of the PCx circuitry.

Animals↗
PubMed2005

Knockout of the neural and heart expressed gene HF-1b results in apical deficits of ventricular structure and activation.

OBJECTIVE: Knockout of the neural and cardiac expressed transcription factor HF-1b causes electrophysiological abnormalities including fatal ventricular arrhythmias that occur with increasing frequency around the 4th week of postnatal life. This study addresses factors that may contribute to conduction disturbance in the ventricle of the HF-1b knockout mouse. Disruptions to gap junctional connexin40 (Cx40) have been reported in distal (i.e., apically located), but not proximal His-Purkinje conduction tissues of the HF-1b knockout mouse. This abnormality in myocardial Cx40 led us to address whether 4-week-old HF-1b knockout postnates display other disruptions to ventricular structure and function. METHODS: Western blotting and immunoconfocal quantification of Cx43 and coronary arteriole density and function were undertaken in the ventricle. Electrical activation was described by optical mapping. RESULTS: Western blotting and immunoconfocal microscopy indicated that overall levels of Cx43 (p<0.001) and percent of Cx43 localized in intercalated disks (p<0.001) were significantly decreased in the ventricular myocardium of knockouts relative to wildtype littermate controls. Analysis of the reduction in Cx43 level by basal and apical territories revealed that the decrease was most pronounced in the lower, apical half of the ventricle of knockouts relative to controls (p<0.001). Myocyte size also showed a significant decrease in the knockout, that was more marked within the apical half of the ventricle (p<0.05). Optical recordings of ventricular activation indicated apically localized sectors of slowed conduction in knockout ventricles not occurring in controls that could be correlated directly to tissues showing reduced Cx43. These discrete sectors of abnormal conduction in the knockout heart were resolved following point stimulation of the ventricular epicardium and thus were not explained by dysfunction of the His-Purkinje system. To further probe base-to-apex abnormalities in the HF-1b knockout ventricle, we analyzed coronary arterial structure and function. These analyses indicated that relative to controls, the apical ventricular territory of the HF-1b knockout had reductions in the density of small resistance vessels (p<0.01) and deficits in arterial function as assayed by bead perfusion (p<0.01). CONCLUSION: The HF-1b knockout ventricle displays abnormalities in Cx43 level, myocyte size, activation spread and coronary arterial structure and function. These abnormalities tend to be more pronounced in the apical territory of the ventricle and seem likely to be factors contributing to the pathological disturbance of cardiac conduction that characterizes the heart of the HF-1b knockout mouse.

Actins↗
PubMed1999

Evidence of three-dimensional scroll waves with ribbon-shaped filament as a mechanism of ventricular tachycardia in the isolated rabbit heart.

INTRODUCTION: Rotating vortices have been observed in excitable media of different nature. Vortices may sustain life or kill in different species, by underlining morphogenesis in Dictiostelium discoideum during starvation, or arrhythmias during sudden cardiac death in mammals. Investigation of vortices in the heart has been limited by two-dimensional experimental techniques. In contrast, three-dimensional (3D) Belousov-Zhabotinsky excitable medium and mathematical models have been shown to sustain scroll-shaped waves. The heart is a 3D structure; therefore, scroll waves may underlie cardiac arrhythmias. METHODS AND RESULTS: We used potentiometric dye and optical mapping techniques to study vortices during ventricular arrhythmias. The core of all observed vortices were linearly shaped and > or = 9 mm (48 episodes, six hearts). As shown by Allessie et al. in the rabbit atrium, ventricular signals recorded within 1 to 2 mm from the line of block were dual humped, suggesting there is electrotonic interaction across the line of block. We hypothesized that the line of block represents epicardial intersection of ribbon-shaped filaments, which in some cases may be oriented under an angle or parallel to the epicardium. In 14 episodes we observed dual-humped optical recordings at one side of the line of block at a distance up to 12 mm. The two humps may represent the signatures of two activation wavefronts propagating above and below the filament, which in this area is close to the epicardial surface. The activation sequence of the two waves is consistent with the idea of a scroll wave with ribbon-like filament. CONCLUSION: Our data provide new insights into the shape and dynamics of the filament of the 3D scroll wave, which underlies the mechanism of ventricular tachycardia in the rabbit heart. The filament of the scroll wave may be ribbon shaped, with a significant width > or = 9 mm and a thickness of 1 to 2 mm. No evidence of fully excitable cells in the core of vortex was observed.

Action Potentials↗
PubMed1984

An optical method of studying the shape and movement of the chest wall in recumbent patients.

A method of optical mapping has been developed that allows the shape and motion of the chest wall to be studied in recumbent patients. It uses a single camera at a fixed viewpoint to determine the three dimensional coordinates of the visible surface of the body, and hence to measure the volume and shape of the visible segment. Measurements on different test objects (volumes 228-7807 ml) in different positions suggest a reproducibility of volume measurement of +/- 26 ml (SD) and a maximum volume error of 150 ml. Studies of computed tomography scans in inspiration and expiration show that it should be possible to capture 97% of respiratory motion by this method. The mean difference between optical and spirometric measurements of expired volume in six subjects was 0.25 (SD 0.2) 1. Within subject systematic errors of up to 10% were noted. The mean deviation about the regression line of optically measured expired volume on spirometric expired volume varied from 68 to 243 ml in the six subjects (mean 131 (SD 92) ml). To examine the potential of the optical technique, for rapid data acquisition it was used to construct a 24 point flow volume loop from a normal subject.

Anthropometry↗
PubMed1993

Distribution of microtubule-associated proteins (MAPs) in adult and embryonic mouse retinal explants: presence of the embryonic map, MAP5/1B, in regenerating adult retinal axons.

Microtubule-associated proteins (MAPs) are developmentally regulated proteins involved in microtubule polymerization and stabilization. We have asked whether MAPs in regenerating adult mouse retinal ganglion cell axons recapitulate the pattern of MAPs seen during development. Adult and Embryonic Day 15 (E15) mouse retinal segments were explanted onto laminin-coated coverslips and allowed to extend neurites in serum-free medium. Using a variety of monoclonal antibodies (Mabs), we stained adult and E15 explant cultures for early (MAP5) and late (MAP1, MAP2, MAP2a+b, tau) MAPs. Optic neurites growing from E15 explants were strongly immunoreactive for MAP5. Labeling was absent for MAP1 and MAP2a+b. Mabs to MAP2 and tau lightly stained axons and cell bodies, probably due to MAP2c and juvenile tau which are found in developing neurons. In adult explant cultures, both perikarya and axons were immunoreactive for MAP1. MAP2 and MAP2a+b labeled perikarya and fibers within the explant, and tau stained axons on the substrate. MAP5 immunoreactivity was intense in the adult explant cultures, labeling axons extending over the substrate and perikarya and dendrites in the explant in a pattern similar to that seen in E15 explants. In summary, adult retinal explants maintain their adult complement of MAPs, in showing high levels of MAP1, tau immunoreactivity restricted to neurites on the substrate, and MAP2 segregated into neurites and perikarya within the explant. The exception is MAP5 for which the pattern of immunoreactivity is similar in adult and E15 retinal explants.

Animals↗
PubMed2004

Fluorescence imaging of electrical activity in cardiac cells using an all-solid-state system.

Tracking spatial and temporal determinants of cardiac arrhythmogenesis at the cellular level presents challenges to the optical mapping techniques employed. In this paper, we describe a compact system combining two nontraditional low-cost solutions for excitation light sources and emission filters in fluorescence measurements of transmembrane potentials, Vm, or intracellular calcium, [Ca2+]i in cardiac cell networks. This is the first reported use of high-power blue and green light emitting diodes (LEDs), to excite cell monolayers stained with Vm - (di-8-ANEPPS) or [Ca2+]i - (Fluo-3) sensitive dyes. In addition, we use simple techniques for fabrication of suitable thin emission filters with uniform properties, no auto-fluorescence, high durability and good flexibility for imaging Vm or [Ca2+]i. The battery-operated LEDs and the fabricated emission filters, integrated with a fiber-optic system for contact fluorescence imaging, were used as tools to characterize conduction velocity restitution at the macro-scale. The versatility of the LEDs for illumination is further emphasized through 1) demonstration of their usage for epi-illumination recordings at the single-cell level, and 2) demonstration of their unique high-frequency light modulation ability. The LEDs showed excellent stability as excitation light sources for fluorescence measurements; acceptable signal-to-noise ratio and negligible cell photodamage and indicator dye photobleaching were observed.

Action Potentials↗
PubMed1999

Multisite optical recording of excitability in the enteric nervous system.

A multisite optical recording technique consisting of an array of 464 photodiodes was used to measure dynamic changes in transmembrane potentials (Vm) of guinea-pig and mouse enteric neurones stained with the voltage-sensitive dye Di-8-ANEPPS. Optical recordings of Vm changes in enteric neurones which were evoked by depolarizing current pulses or synaptic activation mirrored the Vm changes measured intracellularly in the same neurone. Action potentials had fractional change in fluorescence of -0.09 +/- 0.06% and their peak to peak noise level was 20 +/- 14% of the action potential amplitude. Optical recordings after electrical stimulation of interganglionic nerve strands revealed slow EPSPs, nicotinergic supra- and subthreshold fast EPSPs as well as propagation of action potentials along interganglionic strands. Local application of acetylcholine onto a single ganglion induced reproducibly and dose dependently action potential discharge demonstrating the feasibility of neuropharmacological studies. The optical mapping made it possible to record action potentials simultaneously in a large number of neurones with high spatiotemporal resolution that is unattainable by conventional techniques. This technique presents a powerful tool to study excitability spread within enteric circuits and to assess differential activation of enteric populations in response to a number of stimuli which modulate neuronal activity directly or through synaptic mechanisms.

Acetylcholine↗
PubMed1998

Progressive depolarization: a unified hypothesis for defibrillation and fibrillation induction by shocks.

Experimental studies of defibrillation have burgeoned since the introduction of the upper limit of vulnerability (ULV) hypothesis for defibrillation. Much of this progress is due to the valuable work carried out in pursuit of this hypothesis. The ULV hypothesis presented a unified electrophysiologic scheme for linking the processes of defibrillation and shock-induced fibrillation. In addition to its scientific ramifications, this work also raised the possibility of simpler and safer means for clinical defibrillation threshold testing. Recent results from an optical mapping study of defibrillation suggest, however, that the experimental data supporting the ULV hypothesis could instead be interpreted in a manner consistent with traditional views of defibrillation such as the critical mass hypothesis. This review will describe the evidence calling for such a reinterpretation. In one regard the ULV hypothesis superseded the critical mass hypothesis by linking the defibrillation and shock-induced fibrillation processes. Therefore, this review also will discuss the rationale for developing a new defibrillation hypothesis. This new hypothesis, progressive depolarization, uses traditional defibrillation concepts to cover the same ground as the ULV hypothesis in mechanistically unifying defibrillation and shock-induced fibrillation. It does so in a manner consistent with experimental data supporting the ULV hypothesis but which also takes advantage of what has been learned from optical studies of defibrillation. This review will briefly describe how this new hypothesis relates to other contemporary viewpoints and related experimental results.

Animals↗
PubMedDate not supplied

Retinal thickness in healthy and diabetic subjects measured using optical coherence tomography mapping software.

PURPOSE: To define the normal retinal thickness in healthy subjects using optical coherence tomography (OCT) mapping software and to assess the ability of OCT to detect early macular thickening in diabetic patients. METHODS: Six radial scans centered on the fixation point were done on 60 healthy eyes and 70 eyes of 35 diabetic patients without macular edema on biomicroscopy. Retinal thickness was measured automatically with OCT mapping software. Mean retinal thickness was compared in subgroups of healthy patients based on age, sex, and eye, and in the eyes of diabetic patients and healthy subjects. Thickening was diagnosed if mean retinal thickness of an area was greater than the mean thickness + 2SD in the corresponding area in healthy subjects; or if the difference between right and left eye exceeded the mean difference + 2 SD in a given area in healthy subjects. RESULTS: In healthy subjects, mean retinal thickness in the central macular area 1000 microm in diameter was 170+/-18 microm. There was no significant difference according to age, or left or right eye, but central macular thickness was significantly greater in men than women (p=0.0139). No difference was observed between the eyes of healthy subjects and diabetic patients without macular edema on biomicroscopy, but OCT detected early macular thickening in 12 diabetic eyes. CONCLUSIONS: In this study average retinal thickness and mean local variations in a normal population were defined using a commercially available mapping software. OCT seems a sensitive tool for detecting early retinal thickening.

Adult↗
PubMed2003

Examination of optical depth effects on fluorescence imaging of cardiac propagation.

Optical mapping with voltage-sensitive dyes provides a high-resolution technique to observe cardiac electrodynamic behavior. Although most studies assume that the fluorescent signal is emitted from the surface layer of cells, the effects of signal attenuation with depth on signal interpretation are still unclear. This simulation study examines the effects of a depth-weighted signal on epicardial activation patterns and filament localization. We simulated filament behavior using a detailed cardiac model, and compared the signal obtained from the top (epicardial) layer of the spatial domain with the calculated weighted signal. General observations included a prolongation of the action upstroke duration, early upstroke initiation, and reduction in signal amplitude in the weighted signal. A shallow filament was found to produce a dual-humped action potential morphology consistent with previously reported observations. Simulated scroll wave breakup exhibited effects such as the false appearance of graded potentials, apparent supramaximal conduction velocities, and a spatially blurred signal with the local amplitude dependent upon the immediate subepicardial activity; the combination of these effects produced a corresponding change in the accuracy of filament localization. Our results indicate that the depth-dependent optical signal has significant consequences on the interpretation of epicardial activation dynamics.

Action Potentials↗
PubMed2002

Mechanisms of make and break excitation revisited: paradoxical break excitation during diastolic stimulation.

Onset and termination of electric stimulation may result in "make" and "break" excitation of the heart tissue. Wikswo et al. (30) explained both types of stimulations by virtual electrode polarization. Make excitation propagates from depolarized regions (virtual cathodes). Break excitation propagates from hyperpolarized regions (virtual anodes). However, these studies were limited to strong stimulus intensities. We examined excitation during weak near-threshold diastolic stimulation. We optically mapped electrical activity from a 4 x 4-mm area of epicardium of Langendorff-perfused rabbit hearts (n = 12) around the pacing electrode in the presence (n = 12) and absence (n = 2) of 15 mM 2,3-butanedione monoxime. Anodal and cathodal 2-ms stimuli of various intensities were applied. We imaged an excitation wavefront with 528-micros resolution. We found that strong stimuli (x5 threshold) result in make excitation, starting from the virtual cathodes. In contrast, near-threshold stimulation resulted in break excitation, originating from the virtual anodes. Characteristic biphasic upstrokes in the virtual cathode area were observed. Break and make excitation represent two extreme cases of near-threshold and far-above-threshold stimulations, respectively. Both mechanisms are likely to contribute during intermediate clinically relevant strengths.

Action Potentials↗
PubMedDate not supplied

Optical measurement of the change in trunk volume with breathing.

Optical mapping provides three-dimensional information about the size and shape of the trunk. We have used the technique to measure and partition the volume change of the trunk with breathing in upright subjects. In 13 subjects, 12 of whom were normal and one scoliotic, respired volume could be measured with an average error (+/- SEM) of 170 +/- 20 ml. In one of the normal subjects, 24 measurements of respired volume were in error by, on average, 120 +/- 20 ml. In a further eight normal subjects, partitioning of ventilation showed that the anterior trunk contributed 91 +/- 12%, the back 9 +/- 12%, the upper trunk 43 +/- 4%, the lower trunk 57 +/- 4% and the right and left sides 50 +/- 2% each, to a vital capacity expiration. The measurements of respired volume suggest that the technique is sufficiently accurate for clinical purposes, but it offers the added advantage that the information generated can be used to determine the spatial distribution of each breath.

Adult↗
PubMed2000

Virtual sources associated with linear and curved strands of cardiac cells.

Transmembrane potential (V(m)) responses in cardiac strands with different curvature were characterized during uniform electric-field stimulation with the use of modeling and experimental approaches. Linear and U-shaped strands (width 100-150 micrometer) were stained with voltage-sensitive dye. V(m) was measured by optical mapping across the width and at sites of beginning curvature. Field pulses were applied transverse to the strands during the action-potential plateau. For linear strands, V(m) contained 1) a rapid passive component (V(m)(ar)) nearly linear and symmetric across the width, 2) a slower hyperpolarizing component (V(m)(as)) greater and faster on the anodal side, and 3) at high field strengths a delayed depolarizing component (V(m)(ad)) greater on the anodal side. For U-shaped strands, V(m) at sites of beginning curvature also contained rapid and slow components (V(m)(br) and V(m)(bs), respectively) that included contributions from the linear strand response and from the fiber curvature. V(m)(ar), V(m)(br), and part of V(m)(bs) could be attributed to passive behavior that was modeled, and V(m)(as), V(m)(ad), and part of V(m)(bs) could be attributed to active membrane currents. Thus curved strands exhibit field responses separable into components with characteristic amplitude, spatial, and temporal signatures.

Animals↗
PubMed2006

The kinetics of spontaneous calcium oscillations and arrhythmogenesis in the in vivo heart during ischemia/reperfusion.

BACKGROUND: The correlation between spontaneous calcium oscillations (S-CaOs) and arrhythmogenesis has been investigated in a number of theoretical and experimental in vitro models. There is an obvious lack of studies that directly investigate how the kinetics of S-CaOs correlates with a specific arrhythmia in the in vivo heart. OBJECTIVES: The purpose of the study is to investigate the correlation between the kinetics of S-CaOs and arrhythmogenesis in the intact heart using an experimental model of ischemia/reperfusion (I/R). METHODS: Perfused Langendorff guinea pig (GP) hearts were subjected to global I/R (10-15 minutes/10-15 minutes). The heart was stained with a voltage-sensitive dye (RH237) and loaded with a Ca2+ indicator (Rhod-2 AM). Membrane voltage (Vm) and intracellular calcium transient (Ca(i)T) were simultaneously recorded with an optical mapping system of two 16 x 16 photodiode arrays. S-CaOs were considered to arise from a localized focal site within the mapped surface when these preceded the associated membrane depolarizations by 2-15 ms. RESULTS: In 135 episodes of ventricular arrhythmias from 28 different GP experiments, 23 were linked to S-CaOs that were considered to arise from or close to the mapped epicardial window. Self-limited or sustained S-CaOs had a cycle length of 130-430 ms and could trigger propagated ventricular depolarizations. Self-limited S-CaOs that followed the basic beat action potential (AP)/Ca(i)T closely resembled phase 3 early afterdepolarizations. Fast S-CaOs could remain confined to a localized site (concealed) or exhibit varying conduction patterns. This could manifest as (1) an isolated premature beat (PB), bigeminal, or trigeminal rhythm; (2) ventricular tachycardia (VT) when a regular 2:1 conduction from the focal site develops; or (3) ventricular fibrillation (VF) when a complex conduction pattern results in wave break and reentrant excitation. CONCLUSIONS: The study examined, for the first time in the intact heart, the correlation between the kinetics of focal S-CaOs during I/R and arrhythmogenesis. S-CaOs may remain concealed or manifest as PBs, VT, or VF. A "benign looking" PB during I/R may represent "the tip of the iceberg" of an underlying potentially serious arrhythmic mechanism.

Action Potentials↗
PubMed2005

Discovery of gradient pattern in dominant frequency maps during fibrillation: implication of rotor drift and epicardial conduction velocity changes.

Dominant frequency (DF) maps for mapping epicardial activations of ventricular fibrillation (VF) have been studied mainly using fast Fourier transform (FFT). Small and discrete DF domains exhibited in these DF maps have undermined the hypothesis of mother rotor for VF maintenance. We applied continuous Fourier transform (CFT) to generate high-precision DF maps and studied characteristics of these high-precision DF maps. Optical epicardial activations were recorded in isolated rabbit hearts (n=10). Continuous Fourier transform of 1-second segments was performed in VF (n=188) and ventricular tachycardia (n=189) at 0.1 Hz precisions. Banded gradient patterns of gradual change in DF values were observed in 136 of 188 VF segments, but not in ventricular tachycardia. These gradients were not observed when FFT was used. Gradients were observed along the conduction path of reentrant-like waves with decreasing DF values along the path. Spectra in the gradients did not exhibit bimodal spectra as is usually observed in traditional DF domain boundaries. Time-space plots revealed clear association between gradient pattern and epicardial conduction velocity changes. Prior simulation studies predicted a gradient in activation rate during rotor drift. This gradient pattern has been observed for the first time experimentally by only using CFT, but not FFT. High-precision DF videos indicated the existence of gradient movement from one spatial location to another, smoothly instead of randomly disappearing from one location and appearing in another. The discovery of associated pseudoconduction velocity changes, and gradient patterns might suggest that dominant rotor (mother rotor) drifting plays a maintenance role only detectable by CFT and not FFT.

Animals↗
PubMed1992

Spatiotemporal irregularities of spiral wave activity in isolated ventricular muscle.

Voltage-sensitive dyes and high resolution optical mapping were used to analyze the characteristics of spiral waves of excitation in isolated ventricular myocardium. In addition, analytical techniques, which have been previously used in the study of the characteristics of spiral waves in chemical reactions, were applied to determine the voltage structure of the center of the rotating activity (ie, the core). During stable spiral wave activity local activation occurs in a periodic fashion (ie, 1:1 stimulus: response activation ratio) throughout the preparation, except at the core, which is a small elongated area where the activity is of low voltage and the activation ratio is 1:0. The voltage amplitude increases gradually from the center of the core to the periphery. In some cases, however, regular activation patterns at the periphery may coexist with irregular local activation patterns near the core. Such a spatiotemporal irregularity is attended by variations in the core size and shape and results from changes in the core position. The authors conclude that functionally determined reentrant activity in the heart may be the result of spiral waves of propagation and that local spatiotemporal irregularities in the activation pattern are the result of changes in the core position.

Animals↗
PubMed2002

Cardiomyocyte cultures with controlled macroscopic anisotropy: a model for functional electrophysiological studies of cardiac muscle.

Structural and functional cardiac anisotropy varies with the development, location, and pathophysiology in the heart. The goal of this study was to design a cell culture model system in which the degree, change in fiber direction, and discontinuity of anisotropy can be controlled over centimeter-size length scales. Neonatal rat ventricular myocytes were cultured on fibronectin on 20-mm diameter circular cover slips. Structure-function relationships were assessed using immunostaining and optical mapping. Cell culture on microabraded cover slips yielded cell elongation and coalignment in the direction of abrasion, and uniform, macroscopically continuous, elliptical propagation with point stimulation. Coarser microabrasion (wider and deeper abrasion grooves) increased longitudinal (23.5 to 37.2 cm/s; r=0.66) and decreased transverse conduction velocity (18.1 to 9.2 cm/s; r=-0.84), which resulted in increased longitudinal-to-transverse velocity anisotropy ratios (1.3 to 3.7, n=61). A thin transition zone between adjacent uniformly anisotropic areas with 45 degrees or 90 degrees difference in fiber orientation acted as a secondary source during 2x threshold field stimulus. Cell culture on cover slips micropatterned with 12- or 25- micro m wide fibronectin lines and previously coated with decreasing concentrations of background fibronectin yielded transition from continuous to discontinuous anisotropic architecture with longitudinally oriented intercellular clefts, decreased transverse velocity (16.9 to 2.6 cm/s; r=-0.95), increased velocity anisotropy ratios (1.6 to 5.6, n=70), and decreased longitudinal velocity (36.4 to 14.6 cm/s; r=-0.85) for anisotropy ratios >3.5. Cultures of cardiac myocytes with controlled degree, uniformity and continuity of structural, and functional anisotropy may enable systematic 2-dimensional in vitro studies of macroscopic structure-related mechanisms of reentrant arrhythmias. The full text of this article is available at http://www.circresaha.org.

Action Potentials↗
PubMed2004

Contrasting effects of ischemia on the kinetics of membrane voltage and intracellular calcium transient underlie electrical alternans.

Repolarization alternans has been considered a strong marker of electrical instability. The objective of this study was to investigate the hypothesis that ischemia-induced contrasting effects on the kinetics of membrane voltage and intracellular calcium transient (Ca(i)T) can explain the vulnerability of the ischemic heart to repolarization alternans. Ischemia-induced changes in action potential (AP) and Ca(i)T resulting in alternans were investigated in perfused Langendorff guinea pig hearts subjected to 10-15 min of global no-flow ischemia followed by 10-15 min of reperfusion. The heart was stained with 100 microl of rhod-2 AM and 25 microl of RH-237, and AP and Ca(i)T were simultaneously recorded with an optical mapping system of two 16 x 16 photodiode arrays. Ischemia was associated with shortening of AP duration (D) but delayed upstroke, broadening of peak, and slowed decay of Ca(i)T resulting in a significant increase of Ca(i)T-D. The changes in APD were spatially heterogeneous in contrast to a more spatially homogeneous lengthening of Ca(i)T-D. Ca(i)T alternans could be consistently induced with the introduction of a shorter cycle when the upstroke of the AP occurred before complete relaxation of the previous Ca(i)T and generated a reduced Ca(i)T. However, alternans of Ca(i)T was not necessarily associated with alternans of APD, and this was correlated with the degree of spatially heterogeneous shortening of APD. Sites with less shortening of APD developed alternans of both Ca(i)T and APD, whereas sites with greater shortening of APD could develop a similar degree of Ca(i)T alternans but slight or no APD alternans. This resulted in significant spatial dispersion of APD. The study shows that the contrasting effects of ischemia on the duration of AP and Ca(i)T and, in particular, on their spatial distribution explain the vulnerability of ischemic heart to alternans and the increased dispersion of repolarization during alternans.

Action Potentials↗