VOLTAGE DEPENDENCE OF CONTRACTION AND CALCIUM CURRENT IN SEVERELY HYPERTROPHIED FELINE VENTRICULAR MYOCYTES

In the present study the voltage dependence of contraction and the characteristics of the "L-type" Ca2+ current (ICa) were compared in control (C) and severely hypertrophied (H) myocytes (M). Hypertrophy was induced in young cats by slow progressive pressure overload of the feline right ventricle. The amount of hypertrophy induced in this study was more severe than previously examined in this laboratory. The major findings of this study were: (1) The voltage dependence of contraction was not significantly different in C and HM. Peak shortening occurred at 6.2 ± 1.2 mV in HM and at 9.5 ± 1.3 mV in CM. (2) The magnitude of peak ICa density was significantly smaller in HM (5.56 ± 0.53 pA/pF; n = 17) than in Cm (7.09 ± 0.42 pA/pF; n = 20). In both groups of cells ICa reached a maximum at + 10 mV. (3) There were no significant changes in the voltage dependence of both ICa activation and steady-state inactivation. This is the first sutdy to provide evidence that ICa density is reduced in severe hypertrophy. The 21% decrease in peak ICa density could reduce the contractile state of the heart if calcium-induced calcium release is normal and the reduction of ICa alters the Ca2+ released from the sacroplasmic reticulum. The reduction in "L-type" Ca2+ current density in severely hypertrophied myocytes may play a role in the transition from the compensated hypertrophic state to congestive heart failure. Data are means ± standard error. © 1991.