Na-Ca exchange in vascular smooth muscle sarcolemmal vesicles is voltage sensitive and inhibitable by quinidine and diltiazem
These studies were performed to characterize Na-Ca exchange in a sarcolemmal enriched vesicle fraction, obtained by Mg aggregation and differential centrifugation of homogenized bovine superior mesenteric artery (SMA). To avoid the effects of Ca or Na diffusion potentials on the translocation of the counter ion, the transport of /sup 45/Ca or /sup 22/Na was measured in vesicles which were short-circuited by presetting K/sub in/ = k/sub out/ in the presence of the K ionophore, valinomycin. The uptake of 0.1 mM Ca/sub out/ was stimulated 30% by 150 mM Na/sub in/ versus N-methylglucamine/sub in/, in a control cation. The uptake of ImM Na/sub out/ was stimulated 61% by 10 mM Ca/sub in/ versus Mn/sub in/. The efflux of ImM Na/sub in/ was stimulated 57% by 10 mM Ca/sub out/ versus Mn/sub out/. Thus, these vesicles mediate Na/Ca exchange. The one sec Na gradient-dependent uptake of 0.1 mM Ca/sub out/ was .08 nmol/mg under short-circuited conditions. When the membrane potential was rendered inside positive by an inwardly directed K gradient plus valinomycin, Na gradient-dependent Ca uptake increased to 0.17 nmol/mg. The Na gradient-dependent uptake of 0.1 mM Ca/sub out/ was inhibited 12, 6, 82, and 70% by (in mM) 5 choline, 3 amiloride, 5 quinidine, and 5 diltiazem, respectively. It is concluded that Na-Ca exchange in the sarcolemmal of bovine SMA is voltage sensitive, and inhibitable by quinidine and diltiazem. Depolarization stimulated Ca influx in vascular smooth muscle cells may occur, in part, via Na-Ca exchange.
- Research Organization:
- Univ. of Texas Medical School, Houston
- OSTI ID:
- 6992037
- Report Number(s):
- CONF-8604222-
- Journal Information:
- Fed. Proc., Fed. Am. Soc. Exp. Biol.; (United States), Vol. 45:4; Conference: 70. annual meeting of the Federation of American Society for Experimental Biology, St. Louis, MO, USA, 13 Apr 1986
- Country of Publication:
- United States
- Language:
- English
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