| Abstract
| - SUMMARY. Papillary muscles isolated from the left ventricle of 17-20 day old Syrian hamsters with genetic cardiomyopathy (BIO14.6 strain) were examined for their mechanophysiological response to the beta adrenoceptor agonist isoprenaline. The indices of isometric twitch for both myopathic and aged matched normal (BIO RB strain) hamster papillary muscles were statistically the same before exposure to catecholamine. Isoprenaline, however, elicited an exaggerated degree of positive inotropism in myopathic papillary muscles. In addition, the characteristic relaxing effect of beta adrenoceptor agonists (abbreviation of twitch duration) was virtually absent in myopathic muscles. These results suggest that under conditions resembling sympathetic stimulation sarcolemma and perhaps sarcoplasmic reticulum become inadequate regulators of calcium, predisposing young myopathic heart cells to accrue damaging concentrations of sarcoplasmic calcium.
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