AJP - Cell Physiology, Vol 259, Issue 2 C302-C309, Copyright © 1990 by American Physiological Society
Energy dependence of sodium-calcium exchange in vascular smooth muscle cells
J. B. Smith and L. Smith
Department of Pharmacology, School of Medicine, University of Alabama, Birmingham 35294.
Three different types of mitochondrial poisons (oligomycin, antimycin A,
and dinitrophenol) strongly inhibited Na(+)-Ca2+ exchange in aortic
myocytes. Exchange activity was assayed as 45Ca2+ uptake that depended on
inverting the Na+ gradient and was inhibited by 25 microM dimethylbenzamil.
Glucose markedly decreased the inhibition of exchange activity by these
three poisons. Glucose also prevented rotenone from inhibiting exchange and
depleting cellular ATP. In the absence of glucose, rotenone decreased ATP
and exchange activity with half-times of 0.8 and 0.9 min, respectively.
Almost eliminating cellular ATP with rotenone maximally inhibited exchange
by 80%. Repletion of ATP with glucose substantially restored Na(+)-Ca2+
exchange activity. Ca2+ uptake by organelles, subsequent to entry via
exchange for Na+, does not appear to contribute significantly to exchange
activity as assayed in intact myocytes. The specific activity of Na(+)-Ca2+
exchange was approximately 30 nmol.min-1.mg protein-1. These findings
suggest that ATP modulates exchange activity and that there are
approximately 150,000 Na(+)-Ca2+ exchangers per cell, assuming that the
turnover number is 1,000 s-1.
