title: Ion specificity of cardiac sarcolemmal Na+/H+ antiporter.
abstract: In bovine cardiac sarcolemmal vesicles, an outward H+ gradient stimulated the initial rate of amiloride-sensitive uptake of 22Na+, 42K+, or 86Rb+. Release of H+ from the vesicles was stimulated by extravesicular Na+, K+, Rb+, or Li+ but not by choline or N-methylglucamine. Uptakes of Na+ and Rb+ were half-saturated at 3 mM Na+ and 3 mM Rb+, but the maximal velocity of Na+ uptake was 1.5 times that of Rb+ uptake. Na+ uptake was inhibited by extravesicular K+, Rb+, or Li+, and Rb+ uptake was inhibited by extravesicular Na+ or Li+. Amiloride-sensitive uptake of Na+ or Rb+ increased with increase in extravesicular pH and decrease in intravesicular pH. In the absence of pH gradient, there were stimulations of Na+ uptake by intravesicular Na+ and K+ and of Rb+ uptake by intravesicular Rb+ and Na+. Similarly, there were trans stimulations of Na+ and Rb+ efflux by extravesicular alkali cations. The data suggest the existence of a nonselective antiporter catalyzing either alkali cation/H+ exchange or alkali cation/alkali cation exchange. Since increasing Na+ caused complete inhibition of Rb+/H+ exchange, but saturating K+ caused partial inhibitions of Na+/H+ exchange and Na+/Na+ exchange, the presence of a Na(+)-selective antiporter is also indicated. Although both antiporters may be involved in pH homeostasis, a role of the nonselective antiporter may be in the control of Na+/K+ exchange across the cardiac sarcolemma.
authors.affiliation: Department of Pharmacology, Medical College of Ohio, Toledo 43699-0008.
authors.forename: S M
authors.initials: SM
authors.lastname: Periyasamy
authors.forename: S S
authors.initials: SS
authors.lastname: Kakar
authors.forename: K D
authors.initials: KD
authors.lastname: Garlid
authors.forename: A
authors.initials: A
authors.lastname: Askari
mesh_terms: D000818:Animals; D001667:Binding, Competitive; D002352:Carrier Proteins / Q000378:metabolism*; D002414:Cations, Monovalent; D002417:Cattle; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D009206:Myocardium / Q000378:metabolism*; D011188:Potassium / Q000378:metabolism; D012413:Rubidium / Q000378:metabolism; D012508:Sarcolemma / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism*; D017923:Sodium-Hydrogen Exchangers
chemical_list: D002352:Carrier Proteins; D002414:Cations, Monovalent; D017923:Sodium-Hydrogen Exchangers; D012964:Sodium; D012413:Rubidium; D011188:Potassium