EFFECT OF CALCIUM AND HIGH-ENERGY PHOSPHATE COMPOUNDS ON MYOCARDIAL CONTRACTURE IN NEWBORN AND ADULT RABBIT

Anoxic myocardial contracture was studied in the arterially perfused septal preparation of the newborn and adult rabbit. Myocardial energy requirement was varied by changing the pacing rate, and myocardial energy supplies were varied by altering the perfusion rate or adding iodoacetate to the perfusate. Myocardial contracture began at an ATP concentration of 16μmol/g dry weight. Full myocardial contracture was observed at a higher ATP concentration in the newborn as compared with the adult. In the absence of external calcium the onset of myocardial contracture was delayed and the degree of contracture was attenuated. At similar ATP concentrations myocardial contracture was significantly (P < 0.01) less in the quiescent group and groups perfused with calcium-free perfusate. The results indicate that two types of myocardial contracture exist: (1) calcium-sensitive ATP-dependent contracture and (2) calcium-independent, ATP-dependent contracture. © 1978.