The Sodium‐Induced Efflux of Calcium from Heart Mitochondria

The interrelations between the transport of Na + and Ca 2+ in heart mitochondria have been investigated. Na + induces a partial release of Ca 2+ from heart mitochondria; in the presence of ruthenium red the release of Ca 2+ by Na + is complete. The rate of Ca 2+ release appears to be a function of [Na + ] 3 and is stimulated by energy‐linked respiration. Ca 2+ efflux is also induced by Li + although Na + is the preferred cation. The data are consistent with the existence of a system able to catalyze an exchange between Na + (or Li + ) and Ca 2+ across the inner membrane of heart mitochondria.