Stimulation by nifedipine of calcium transport by cardiac sarcolemmal vesicles from spontaneously hypertensive rats.

The effects of the calcium antagonist nifedipine on the binding and ATP-dependent accumulation of calcium by cardiac plasma membranes from spontaneously hypertensive rats (SHR) and from their normotensive controls (WKY) were studied at free calcium concentrations of 2 X 10(-8) M and 4 X 10(-7) M corresponding to very high affinity and high affinity binding sites respectively. Nifedipine did not significantly modify calcium binding to either class of sites in SHR or WKY membranes. In contrast, in a free calcium concentration of 2 X 10(-8) M, nifedipine enhanced ATP-dependent Ca2+ transport. The concentration of nifedipine required for significant stimulation was smaller in SHR than in WKY membranes (10(-7) M and 10(-5) M respectively). Another calcium antagonist, D600, did not modify ATP-dependent calcium accumulation by SHR or WKY vesicles. These results raise the question of the mechanism of action of nifedipine on the calcium pump and confirm the presence of abnormalities in cardiac plasma membranes from young SHR, rendering them more sensitive than WKY membranes to the calcium antagonist nifedipine.