Four steps to two sexes

Cell length was measured in single guinea-pig left ventricular myocytes by using a high-resolution photodiode array. Step depolarizations from a holding potential of --45 mV were applied using a switch-clamp technique with 2 M KCl microelectrodes, which were devoid of Ca$^{2+}$ buffering. Comparison was made between myocytes from sham-operated guinea-pigs and guinea-pigs with mild pressure-overload left ventricular hypertrophy induced by infra-renal aortic constriction. The relation between cell shortening and membrane voltage was bell shaped, and a phasic component of shortening was evident at the range of potentials over which the L-type calcium current was activated. Mean cell shortening was increased in the hypertrophy group, and was maximal at + 15 mV in both groups (control, 7.6 $\pm $ 0.9 $\mu $m, n = 11, hypertrophy 11.0 $\pm $ 1.2 $\mu $m, n = 20, p < 0.05). The latency to the onset of contraction was significantly 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 very 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--calcium exchange in the myocytes from the hypertrophy group.