Subcellular electrolyte shifts during in vitro myocardial ischemia and reperfusion

Isolated perfused rabbit right ventricular wall was studied with electron probe microanalysis (EPMA) under three conditions: 1) control (37 degrees C, 1.2 Hz), 2) 60 min global ischemia, and 3) ischemia plus 5 min of reperfusion. After 60 min of ischemia, only one cell population was evident; the variance of intracellular electrolyte concentrations was the same as in controls. When compared with controls, there was no change in Ca concentration within any region of the cell, but mitochondria were swollen with K-rich fluid. Two cell populations were evident after 5 min of reperfusion. The severely injured cells were markedly swollen, exhibited hypercontraction bands, and had electrolyte profiles similar to extracellular fluid. The moderately injured cells were normal in appearance, still retained electrolyte gradients, but had elevated Na and Cl concentrations in all compartments. Cell Ca did not increase in the moderately injured cells, but the region of the cell containing the sarcoplasmic reticulum (SR) lost 90% of its Ca. Accompanying this loss were large increases in myofibrillar and mitochondrial Ca concentration. It appears that release of SR Ca, loss of SR Ca-accumulating capacity, and increased intracellular Na are the principal electrolyte shifts in functional cells during early reperfusion.