Dependence of Na+-Ca2+ exchange and Ca2+-Ca2+ exchange on monovalent cations

• Published in: Biochimica et biophysica acta Vol. 729; no. 1; pp. 123 - 136
• Main Authors: Ledvora, R F, Hegyvary, C
• Format: Journal Article
• Language: English
• Published: Netherlands 23.03.1983
• Subjects: Animals; Biological Transport - drug effects; Calcium - metabolism; Cations, Monovalent; Dogs; Heart Ventricles - metabolism; Kinetics; Myocardium - metabolism; Sarcolemma - drug effects; Sarcolemma - metabolism; Sodium - metabolism; Valinomycin - pharmacology
• ISSN: 0006-3002

Two mechanisms of passive Ca2+ transport, Na+-Ca2+ exchange and Ca2+-Ca2+ exchange, were studied using highly-purified dog heart sarcolemmal vesicles. About 80% of the Ca2+ accumulated by Na+-Ca2+ exchange or Ca2+-Ca2+ exchange could be released as free Ca2+, while up to 20% was probably bound. Na+-Ca2+ exchange was simultaneous, coupled countertransport of Na+ and Ca2+. The movement of anions during Na+-Ca2+ exchange did not limit the initial rate of Na+-Ca2+ exchange. Na+-Ca2+ exchange was electrogenic, with a reversal potential of about -105 mV. The apparent flux ratio of Na+-Ca2+ exchange was 4 Na+:1 Ca2+. Coupled cation countertransport by the Na+-Ca2+ exchange mechanism required a monovalent cation gradient with the following sequence of ion activation: Na+ much greater than Li+ greater than Cs+ greater than K+ greater than Rb+. In contrast to Na+-Ca2+ exchange, Ca2+-Ca2+ exchange did not require a monovalent cation gradient, but required the presence of Ca2+ plus a monovalent cation on both sides of the vesicle membrane. The sequence of ion activation of Ca2+-Ca2+ exchange was: K+ much greater than Rb+ greater than Na+ greater than Li+ greater than Cs+. Na+ inhibited Ca2+-Ca2+ exchange when Ca2+-Ca2+ exchange was supported by another monovalent cation. Both Na+-Ca2+ exchange and Ca2+-Ca2+ exchange were inhibited, but with different sensitivities, by external MgCl2, quinidine, or verapamil.