Effect of work on intracellular calcium of the intact heart.

Intracellular calcium has been proposed to play a key role in the orchestration of metabolic rate with contractile activity in the mammalian heart. Calcium is believed to accomplish this task by modulating the contractile apparatus as well as the metabolic process directly, and perhaps simultaneously, during alterations in cardiac work. The purpose of this study was to evaluate whether appropriate changes in intracellular calcium accompany alterations in cardiac work in the intact working rabbit heart. A range of myocardial oxygen consumption was obtained from 0.94 to 6.51 mumol.g LV wt-1.min-1 by changing afterload or beta-agonist addition. With the increase in work and associated increase in respiration, an increase in intracellular calcium was observed, on the basis of indo-1 fluorescence. These results indicate that intracellular calcium is a valid candidate as a cytosolic transducer contributing to the orchestration of myofibril adenosinetriphosphatase activity and oxidative phosphorylation in the intact heart.