Contracture in Isolated Adult Rat Heart Cells Role of Ca, ATP, and Compartmentation

Isolated intact quiescent myocytes from the adult rat were used as a model system for investigating the determinants of contracture induced by metabolic deprivation. The model simulated the pattern of contracture and ATP decline seen in the intact heart during Ischemia. Three new insights into the contracture process were gained: (1) in the quiescent cell system, the rate of onset of contracture was independent of external Cn*, supporting the view that the Ca dependence of the rate of onset in the whole heart is related to beat-dependent substrate utilization; (2) the second phase of ATP decline was paralleled by a decline In the percentage of cells which had not undergone contracture, suggesting that—in any cell—contracture is immediately preceded by a total loss of ATP; and (3) oligomycin delayed the onset of contracture by 55 ± 12%, suggesting that mitochondria! ATPase activity ia a significant drain on energy resources in the quiescent ischemic heart. Ore Res 49:1119-1128, 1981