The Cycling of Calcium, Sodium, and Protons Across the Inner Membrane of Cardiac Mitochondria

Abstract

A method is described that permits simultaneous determination of the net charge transfer associated with Ca2+ transport by the ruthenium‐red‐sensitive carrier and the ionized internal [Ca2+] in heart mitochondria. The data indicate that this carrier catalyses a charge‐uncompensated flux of Ca2+. Full charge compensation for Ca2+ influx is provided by the respiration‐dependent efflux of H+. The net efflux of Ca2+ induced by Na+ is analysed in terms of two other carriers, a Na+‐Ca2+ antiporter and a Na+‐H+ antiporter. Evidence is presented that these two carriers are separate and that the Na+‐H+ exchange is the more rapid. The fluxes of Ca2+, Na+ and H+ during the Na+‐induced efflux of Ca2+ support a series of events in which the Na+‐H+ exchange enables unidirectional Ca2+ fluxes via the uniport and antiport systems to be integrated into a cycle. Copyright © 1978, Wiley Blackwell. All rights reserved