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INTRODUCTION: To determine if collagenase-dispersed epicardial myocytes overlying myocardial infarction reproduce the same altered electrophysiology observed in intact epicardium, multicellular tissue preparations and enzymatically-dispersed myocytes from ischemically-injured canine subepicardium were examined 1 and 4 days after myocardial infarction. METHODS AND RESULTS: The electrophysiologic changes observed with ischemic injury in enzymatically-dispersed myocytes were not different from changes observed in multicellular tissue preparations at 1 and 4 days postinfarction. Ischemically-injured myocytes were depolarized versus normal myocytes at K0+ (2.5 to 40 mM) with reduced membrane potentials also observed in injured subepicardial tissue preparations K0+ (4 to 24 mM). On day 1, the reduced Vmax and the prolonged recovery of Vmax from inactivation were consistent with the reduced membrane potentials observed at each K0+. The half-maximal Vmax, maximal Vmax, and Boltzmann constant (k) in injured myocytes were unchanged versus normal myocytes. On day 4 postinfarction, the half-maximal Vmax was shifted to a more negative membrane potential, the maximal Vmax was reduced, and k was increased in injured versus normal myocytes. Prolonged recovery from inactivation was observed with depressed membrane potentials in injured myocytes on day 4. CONCLUSION: Enzymatically-dispersed myocytes from ischemically-injured subepicardium closely reproduce altered cellular properties observed in multicellular tissue preparations. The data suggest that 1 day postinfarction, altered conduction and refractoriness largely result from a reduced membrane potential. At 4 days, a reduced maximal Vmax, a shift in the inactivation curve to more negative voltages, and prolonged recovery of Vmax from inactivation also contribute to slowed conduction and prolonged refractoriness.
Patterson et al. (Mon,) studied this question.