title: Na-Ca exchange and Ca fluxes during contraction and relaxation in mammalian ventricular muscle.
abstract: There are four cellular Ca transport systems which compete to remove Ca from the myoplasm in mammalian ventricular myocytes. These are 1) the SR Ca-ATPase, 2) the sarcolemmal Na-Ca exchange, 3) the sarcolemmal Ca-ATPase and 4) the mitochondrial Ca uniporter. Using multiple experimental approaches we have evaluated the dynamic interaction of these systems during the normal cardiac contraction-relaxation cycle. The SR Ca-ATPase and Na-Ca exchange are clearly the most important, quantitatively; however, the relative roles vary in a species-dependent manner. In particular, the SR is much more strongly dominant in rat ventricular myocytes, where approximately 92% of Ca removal is via SR Ca-ATPase and only 7% via Na-Ca exchange during a twitch. In other species (rabbit, ferret, cat, and guinea pig) the balance is more in the range of 70% SR CA-ATPase and 25-30% Na-Ca exchange. Ferret ventricular myocytes also exhibit an unusually strong sarcolemmal Ca-ATPase. During the steady state the same amount of Ca must leave the cell as enters over a cardiac cycle. This implies that 25-30% of the Ca required to activate contraction must enter the cell, and experiments demonstrate that this amount of Ca may be supplied by the L-type Ca current.
authors.affiliation: Department of Physiology, Loyola University Chicago, Stritch School of Medicine, Maywood, Illinois 60153, USA.
authors.forename: D M
authors.initials: DM
authors.lastname: Bers
authors.forename: J W
authors.initials: JW
authors.lastname: Bassani
authors.forename: R A
authors.initials: RA
authors.lastname: Bassani
mesh_terms: D000818:Animals; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D000252:Calcium-Transporting ATPases / Q000378:metabolism; D002352:Carrier Proteins / Q000378:metabolism*; D009200:Myocardial Contraction / Q000502:physiology*; D009206:Myocardium / Q000378:metabolism*; D012508:Sarcolemma / Q000201:enzymology; D012964:Sodium / Q000378:metabolism*; D019831:Sodium-Calcium Exchanger; D013696:Temperature; D016276:Ventricular Function
chemical_list: D002352:Carrier Proteins; D019831:Sodium-Calcium Exchanger; D002110:Caffeine; D012964:Sodium; D000252:Calcium-Transporting ATPases; D002118:Calcium