Calcium uptake and storage in isolated heart mitochondria influenced by sodium and potassium ions

With rising concentrations of KCl the rate of Ca2+ uptake was moderately increased by 37 percent. NaCl induced a strong decrease of the rate of Ca2+ uptake from 498 to 194 nmoles of Ca2+ per sec-gm of protein (0-100 mM NAaCl). Elevating the K+/Na+ quotient from 0.1 to 15.7, we found a concomitant alteration of the rate of Ca2+ uptake which is mediated exclusively by sodium ions. These data indicate that with lowering of the K+/Na+ gradient there is a marked diminution of the mitochondrial rate of Ca2+ uptake and Ca storage. Our findings may contribute to answering how Na+-K+ exchange at the cell membrane may influence intracellular Ca2+ binding and Ca2+ turnover.