Extracellular Na+ dependence of changes in free Ca2+, 45Ca2+ efflux, and total cell Ca2+ produced by angiotensin II in cultured arterial muscle cells.
Angiotensin II (ANG II) evoked a rapid efflux of 45Ca2+ which was largely, but not completely, prevented by the removal of extracellular Na+. ANG II had little, if any, effect on a fast component of 45Ca2+ uptake, although the hormone increased a slow component of 45Ca2+ uptake by 2.5-fold. ANG II decreased total cell Ca2+ by about 40% within 1 min of hormone addition. The replacement of extracellular Na+ with N-methyl-D-glucamine or K+ nearly prevented ANG II from decreasing total cell Ca2+. ANG II caused a 5-fold increase in free Ca2+ which reached a peak about 10 s after hormone addition. Free Ca2+ decreased rapidly from the peak to a plateau phase which lasted for several min. Free Ca2+ during the plateau phase was about 1.5 times the basal level. Removing extracellular Na+ caused a more than 2-fold increase in the free Ca2+ concentration that was maintained during the plateau phase, and Na+, added during the plateau phase, rapidly decreased free Ca2+. These findings suggest that the transient nature of the increase in free Ca2+ produced by ANG II is due in part to a net efflux of Ca2+ which is largely dependent on external Na+ and probably mediated by Na+/Ca2+ exchange.
Department of Pharmacology, University of Alabama at Birmingham 35294.
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D000804:Angiotensin II / Q000031:analogs & derivatives / Q000378:metabolism / Q000494:pharmacology*; D000818:Animals; D001572:Benzofurans; D002118:Calcium / Q000378:metabolism*; D002478:Cells, Cultured; D005456:Fluorescent Dyes; D016257:Fura-2; D009131:Muscle, Smooth, Vascular / Q000187:drug effects*; D051381:Rats; D011945:Receptors, Angiotensin / Q000378:metabolism; D012964:Sodium / Q000378:metabolism*
D001572:Benzofurans; D005456:Fluorescent Dyes; D011945:Receptors, Angiotensin; D000804:Angiotensin II; C009210:sarleucin; D012964:Sodium; D002118:Calcium; D016257:Fura-2