title: Demonstration of Na+-dependent Ca2+ efflux using low concentrations of fluorometric Ca2+ probes.
abstract: The effects of different concentrations of the fluorometric Ca2+ probes, fura-2 and indo-1, on Ca2+ transients in cultured rat aortic smooth muscle cells were examined. When stimulated with the agonists, angiotensin II and arginine vasopressin, cells incubated with low concentrations of fura-2 or indo-1 (less than 1 microM) produced Ca2+ transients characterized by a small increase followed by a dramatic decrease in fluorescence below the original baseline. This effect of agonists was concentration-dependent, reversible, and blocked by receptor antagonists. In contrast to the agonists, stimulation of Ca2+ transients with depolarizing concentrations of K+ or with caffeine did not produce decreases in fluorescence and Ca2+ levels at any loading concentration of probe. The decrease in Ca2+ observed with agonists was dependent on the presence of extracellular Na+. These data suggest that under certain loading conditions, fluorescent Ca2+ indicators measure agonist-stimulated Ca2+ efflux mediated by a Na+/Ca2+ exchange mechanism.
authors.affiliation: Department of Pharmacology, College of Medicine, University of South Alabama.
authors.forename: T L
authors.initials: TL
authors.lastname: Cornwell
authors.forename: T M
authors.initials: TM
authors.lastname: Lincoln
mesh_terms: D000818:Animals; D001011:Aorta; D001572:Benzofurans; D002118:Calcium / Q000378:metabolism*; D005456:Fluorescent Dyes; D005470:Fluorometry / Q000379:methods; D016257:Fura-2; D007211:Indoles; D009131:Muscle, Smooth, Vascular / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D051381:Rats; D012964:Sodium / Q000494:pharmacology*
chemical_list: D001572:Benzofurans; D005456:Fluorescent Dyes; D007211:Indoles; D012964:Sodium; C048960:indo-1; D002118:Calcium; D016257:Fura-2