Heterogeneity of the action potential in isolated rat ventricular myocytes and tissue.

Abstract

SUMMARY. The objectives of this study were to measure action potential parameters in enzymedissociated, adult rat ventricular myocytes stimulated at 1 Hz, to compare these measurements with those obtained from intact ventricular tissue, and to determine myocyte and tissue responses at stimulus frequencies between 0.1 and 5 Hz. Action potentials were characterized in terms of amplitude, overshoot, resting potential, duration at 25% and 75% repolarization (APD25, APD75), and V max . Based on statistical differences in APD25 and APD75, myocyte action potentials were classified as type 1 (3.1 ± 1.0 and 21.5 ± 3.6 msec), type II (7.4 ± 1.1 and 38.2 ± 6.7 msec), or type III (14.5 ± 1.9 and 46.0 ± 4.1 msec). Action potentials corresponding to type I were found in right ventricular endocardium and right papillary muscles, and those corresponding to types II and III in the left ventricular endocardium [apex, middle (II); base (III)] and left papillary muscles (II). Myocytes and papillary muscles responded to increases in driving rate with nearly identical lengthening of APD25 and shortening of APD 75 . The one exception was at 5 Hz where a lengthening of the APD75 occurred in some myocytes. We conclude that action potential configuration in rat ventricle is heterogeneous, and that this is reflected by the different types of action potentials in isolated myocytes. It is likely that the magnitude of a transient outward current is a determinant of action potential configuration, and that slow reactivation of this current is a significant factor underlying the stimulus frequency response. (Ore Res 52: 280-290, 1983)

Strontium, nifedipine and 4‐aminopyridine modify the time course of the action potential in cells from rat ventricular muscle

“…It has been pointed out (Powell et al, 1980) that the precise time course of the action potential depends, among other factors, on the resting membrane potential and rate of stimulation. These factors may account for some small differences between the action potentials reported by Powell et al (1980; and the present study) and those of Watanabe et al (1983), in addition to any differences between cells of different origin in rat ventricular muscle (Watanabe et al, 1983). This work was supported by grants from the B.H.F.…”

Effects of diabetic cardiomyopathy on regional electrophysiologic characteristics of rat ventricle

“…The regional disparity of K + currents is responsible for some of the well-known differences in the duration of the rat ventricular action potentials [10,11,21]. Therefore, the relative participation of the currents to the repolarisation process could differ in the different regions, thus, I to participation in control hearts is in RV greater than in EpiALV and in EpiALV greater than in EndoBLV.…”

“…We isolated myocytes from the whole wall of the right ventricle (RV) and from two different regions of the left ventricle, the subepicardium at the apex (EpiALV) and the subendocardium at the base (EndoBLV). These ventricular regions show differences in action potential duration [11]. Myocytes were dispersed by mechanical agitation.…”

“…None took into account, however, the regional variability in the duration of the action potential under control conditions [10,11]. Various reports pointed to a lowering of the transient outward current, I to [9,12,13] and, to a lesser extent, the delayed rectifying outward current, I K [9,12], as the main cause of the lengthening of APD.…”

In vitroarrhythmia generation by mild hypothermia: a pitchfork bifurcation type process

“…The acquired extracellular potential (EP) shares very similar electrophysiological properties of cardiac muscular cell in situ [22]. This model has been a good tool to study related cardiovascular problems, for instance, experiments on arrhythmogenic drugs, ischemia, hypoxia etc.…”