title: Na+-Ca2+ exchange is affected by membrane potential in cardiac sarcolemmal vesicles.
abstract: The effect of membrane potential on the Na+-Ca2+ exchange activity of isolated sarcolemmal vesicles from dog ventricles is examined. Na+-Ca2+ exchange is monitored as Nai+-dependent Ca2+ uptake as described by Reeves and Sutko ((1979) Proc. Natl. Acad. Sci. U. S. A. 76,590-594). Membrane potential is controlled by varying internal and external K+ in the presence of valinomycin. Inside-positive potentials stimulate Nai+-dependent Ca2+ influx. This stimulation is independent of Ca2+ concentration. The results indicate that Na+-Ca2+ exchange by itself can generate a substantial potential (approximately -60mV) in the sarcolemmal vesicles. The data are consistent with an electrogenic Na+-Ca2+ exchange mechanism in which three or more Na+ are exchanged for one Ca2+. This electrogenic exchange may have important implications in the control of myocardial tension development.
mesh_terms: D000818:Animals; D001693:Biological Transport, Active / Q000187:drug effects; D002118:Calcium / Q000378:metabolism*; D004285:Dogs; D006352:Heart Ventricles / Q000378:metabolism; D007700:Kinetics; D008564:Membrane Potentials / Q000187:drug effects; D012508:Sarcolemma / Q000187:drug effects / Q000378:metabolism* / Q000502:physiology; D012964:Sodium / Q000378:metabolism* / Q000494:pharmacology; D014634:Valinomycin / Q000494:pharmacology
chemical_list: D014634:Valinomycin; D012964:Sodium; D002118:Calcium