The effect of Li+ on Na-Ca exchange in cardiac sarcolemmal vesicles.
The effects of Li+ on Na-Ca exchange in bovine cardiac sarcolemmal vesicles were examined. The initial rate of Na(+)-dependent Ca2+ uptake and efflux was inhibited by Li+ in a dose dependent manner. The initial rate of Na(+)-dependent Ca2+ uptake was inhibited 49.8 +/- 2.9% (S.E.) (n = 6) in the presence of Li+ compared to activity in external K+ or choline+. Kinetic analysis indicated that Li+ increased the Km for Ca2+ (96.3 microM) compared to K+ and choline+ (25.5 and 22.9 microM respectively) while Vmax (1.4, 1.2 and 1.1 nmol Ca2+/mg protein/sec respectively) remained unchanged. Li+ did not alter the experimentally derived stoichiometry of the exchange reaction of 3 Na+ for 1 Ca2+.
Hale
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Department of Veterinary Biomedical Sciences, John M. Dalton Research Center, University of Missouri, Columbia 65211.
Keller
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D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002417:Cattle; D002794:Choline / Q000494:pharmacology; D006321:Heart / Q000187:drug effects; D007700:Kinetics; D008094:Lithium / Q000494:pharmacology*; D009206:Myocardium / Q000378:metabolism*; D011188:Potassium / Q000494:pharmacology; D012508:Sarcolemma / Q000187:drug effects* / Q000378:metabolism; D012964:Sodium / Q000378:metabolism*
D008094:Lithium; D012964:Sodium; D002794:Choline; D011188:Potassium; D002118:Calcium