CHANGES IN CELL LENGTH CONSEQUENT ON DEPOLARIZATION IN SINGLE LEFT-VENTRICULAR MYOCYTES FROM GUINEA-PIGS WITH PRESSURE-OVERLOAD LEFT-VENTRICULAR HYPERTROPHY

Cell length was measured in single guinea-pig left ventricular myocyte s by using a high-resolution photodiode array. Step depolarizations fr om a holding potential of -45 mV were applied using a switch-clamp tec hnique with 2 m KCl microelectrodes, which were devoid of Ca2+ bufferi ng. Comparison was made between myocytes from sham-operated guinea-pig s and guinea-pigs with mild pressure-overload left ventricular hypertr ophy induced by infra-renal aortic constriction. The relation between cell shortening and membrane voltage was bell shaped, and a phasic com ponent of shortening was evident at the range of potentials over which the L-type calcium current was activated. Mean cell shortening was in creased in the hypertrophy group, and was maximal at +15 mV in both gr oups (control, 7.6 +/- 0.9 mum, n = 11, hypertrophy 11.0 +/- 1.2 mum, n = 20, p < 0.05). The latency to the onset of contraction was signifi cantly shorter in the hypertrophy myocytes at -25 mV and at potentials positive to +50 mV. The relation between time-to-peak shortening and voltage showed a trend to shorter times in the hypertrophy group. At v ery positive potentials a slow component of contraction was identified which was relatively larger in the hypertrophy myocytes. This finding is consistent with increased calcium entry via sarcolemmal sodium-cal cium exchange in the myocytes from the hypertrophy group.