Intracellular calcium and myocardial function during ischemia.

Cardiac ischemia causes a rapid decline in mechanical performance and, if prolonged, myocardial cell death occurs on reperfusion. The early decline in mechanical performance could, in principle, be caused either by reduced intracellular calcium release or by reduced responsiveness of the myofibrillar proteins to calcium. It is now known that intracellular calcium rises during ischemia and that the early decline in mechanical performance is caused largely by the inhibitory effects of phosphate and protons on the myofibrillar proteins. The rise of intracellular calcium during ischemia is related to the acidosis and is probably caused by calcium influx on the Na/Ca exchanger. This is triggered by a rise in intracellular sodium which enter the cell in exchange for protons on the Na/H exchanger. Intracellular calcium rises still further on reperfusion the elevation of calcium and the degree of muscle damage are closely correlated.