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 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 Ca2+ 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 +/- 0.9 microns, n = 11, hypertrophy 11.0 +/- 1.2 microns, 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.
Department of Cardiovascular Medicine, University of Oxford, John Radcliffe Hospital, Headington, U.K.
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Bryant
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Hart
D000200:Action Potentials; D000818:Animals; D002478:Cells, Cultured; D004558:Electric Stimulation; D005260:Female; D006168:Guinea Pigs; D006321:Heart / Q000502:physiology / Q000503:physiopathology*; D017379:Hypertrophy, Left Ventricular / Q000473:pathology / Q000503:physiopathology*; D009200:Myocardial Contraction; D009206:Myocardium / Q000166:cytology / Q000473:pathology; D012016:Reference Values