Ca2+ compartments in saponin-skinned cultured vascular smooth muscle cells.
A method for saponin skinning of primary cultured rat aortic smooth muscle cells was established. The saponin-treated cells could be stained with trypan blue and incorporated more 45Ca2+ than the nontreated cells under the same conditions. At low free Ca2+ concentration, greater than 85% of 45Ca2+ uptake into the skinned cells was dependent on the extracellularly supplied MgATP. In the intact cells, both caffeine and norepinephrine increased 45Ca2+ efflux. In the skinned cells, caffeine increased 45Ca2+ efflux, whereas norepinephrine did not. The caffeine-releasable 45Ca2+ uptake fraction in the skinned cells appeared at 3 X 10(-7) M Ca2+, increased gradually with the increase in free Ca2+ concentration, and reached a plateau at 1 X 10(-5) M Ca2+. The 45Ca2+ uptake fraction, which was significantly suppressed by sodium azide, appeared at 1 X 10(-5) M Ca2+ and increased monotonically with increasing free Ca2+ concentration. The results suggest that the caffeine-sensitive Ca2+ store, presumably the sarcoplasmic reticulum, plays a physiological role by releasing Ca2+ in response to norepinephrine or caffeine and by buffering excessive Ca2+. The 45Ca2+ uptake by mitochondria appears too insensitive to be important under physiological conditions.
D000818:Animals; D001386:Azides / Q000494:pharmacology; D001693:Biological Transport, Active / Q000187:drug effects; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002451:Cell Compartmentation; D002478:Cells, Cultured; D008928:Mitochondria / Q000378:metabolism; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000378:metabolism*; D009638:Norepinephrine / Q000494:pharmacology; D051381:Rats; D012503:Saponins; D012519:Sarcoplasmic Reticulum / Q000378:metabolism; D019810:Sodium Azide
D001386:Azides; D012503:Saponins; D002110:Caffeine; D019810:Sodium Azide; D002118:Calcium; D009638:Norepinephrine