Intracellular sodium and calcium in the postischemic myocardium

Intracellular sodium and calcium were measured in 30 isolated perfused rat hearts exposed to normothermic ischemic intervals varying from 0 to 40 minutes followed by 35 minutes of reperfusion. Accumulation of these elements was correlated with alterations in postischemic isovolumic contractile function. There were increases in calcium of 207%, 390%, and 681% of the non-ischemic control following reperfusion after respective ischemic intervals of 30, 35, and 40 minutes. These corresponded to decrements in peak developed pressure of 23.8% after 30 minutes, 68.6% after 35 minutes, and no recovery of function after 40 minutes of ischemia. Thirty-five and 40 minutes of ischemia produced 138% and 170% increases in intracellular sodium, respectively. These data show that there is a graded accumulation of intracellular sodium and calcium that correlates with the duration of ischemia and the degree of functional impairment in the postischemic heart. Measurement of intracellular sodium and calcium may, therefore, serve as an adjunct to other biochemical and functional factors used to quantitate postischemic and postcardioplegic damage in the development of new myoprotective regimens.