Contracture in isolated adult rat heart cells. Role of Ca2+, 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 Ca2+, supporting the view that the Ca2+ 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 mitochondrial ATPase activity is a significant drain on energy resources in the quiescent ischemic heart.