title: Relationship between cytosolic free Ca2+ and Na+-Ca2+ exchange in aortic muscle cells.
abstract: We examined the relationship between extracellular Na+ ([Na+]o) and cytosolic free Ca2+ ([Ca2+]i) in primary and passaged cultures of aortic muscle cells. Removing [Na+]o increased [Ca2+]i by approximately 10-fold in cells that were Na+ loaded. Decreasing [Na+]o from 140 to 32 mM caused the half-maximal increase in [Ca2+]i. [Ca2+]i exhibited a sigmoidal dependence on [Na+]o. Mg2+, a competitive inhibitor of Na2+-Ca2+ antiport in these cells, antagonized the increase in [Ca2+]i produced by lowering [Na+]o. High K+ decreased the potency of Mg2+ 6.5-fold as previously reported for Na+ gradient-dependent 45Ca2+ influx. In contrast to the Na+-loaded cells, removing [Na+]o caused no detectable change in [Ca2+]i in cells with normal Na+ even though the calculated electrochemical driving force for Na+-Ca2+ exchange was large enough to almost maximally increase [Ca2+]i in the Na+-loaded cells. We conclude that Na+-Ca2+ antiport activity is latent in the unstimulated cell at basal intracellular Na+ and Ca2+.
authors.affiliation: Department of Pharmacology, University of Alabama, Birmingham 35294.
authors.forename: J B
authors.initials: JB
authors.lastname: Smith
authors.forename: T
authors.initials: T
authors.lastname: Zheng
authors.forename: L
authors.initials: L
authors.lastname: Smith
mesh_terms: D000804:Angiotensin II / Q000494:pharmacology; D000818:Animals; D001011:Aorta; D002118:Calcium / Q000378:metabolism*; D002352:Carrier Proteins / Q000378:metabolism*; D002478:Cells, Cultured; D002794:Choline / Q000494:pharmacology; D003600:Cytosol / Q000378:metabolism; D004563:Electrochemistry; D006801:Humans; D007231:Infant, Newborn; D007811:Lanthanum / Q000494:pharmacology; D008094:Lithium / Q000494:pharmacology; D008274:Magnesium / Q000494:pharmacology; D008536:Meglumine / Q000494:pharmacology; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000378:metabolism*; D011188:Potassium / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D012964:Sodium / Q000378:metabolism / Q000494:pharmacology; D019831:Sodium-Calcium Exchanger
chemical_list: D002352:Carrier Proteins; D019831:Sodium-Calcium Exchanger; D000804:Angiotensin II; D008536:Meglumine; D007811:Lanthanum; D008094:Lithium; D012964:Sodium; D008274:Magnesium; D002794:Choline; D011188:Potassium; D002118:Calcium