Relationship between cellular calcium and prostaglandin synthesis in cultured vascular smooth muscle cells

Abstract

We have investigated the effects of extracellular and intracellular Ca deficits and of pharmacologic agents thought to inhibit Ca influx or intracellular Ca mobilization on vasopressin-evoked changes of cytosolic Ca 2+ levels and PG synthesis in cultured rat mesenteric arterial vascular smooth muscle cells. Vasopressin rapidly increased cytosolic Ca 2+ as well as PG synthesis. The increase of cytosolic Ca 2+ and the rate of PG synthesis were both maximal within the first minute of incubation. An extracellular Ca deficit of short duration partially inhibited both vasopressin-evoked PG synthesis and the increase of cytosolic Ca 2+ by 40 to 60%. Two procedures which deplete cells of some of their intracellular Ca, namely a 30 min incubation in EGIA-supplemented, Ca-lacking media, or a 1 min incubation with ionophore A23187 in Ca-deficient media, decreased PG synthesis by 65% to 100%. The addition of extracellular Ca to Ca-depleted cells restored the ability of vasopressin to stimulate PG synthesis. Two Ca channel antagonists, nifedipine or cinnarizine, had no effect on either vasopressin-evoked PG synthesis or increased cytosolic Ca 2+, whereas TMB-8 (10 μM), a putative inhibitor of intracellular Ca mobilization, decreased PG synthesis by 75% by inhibiting acylhydrolase as well as cyclo-oxygenase activities, but had no effect on basal or vasopressin-evoked increase of cytosolic Ca 2+, documenting that its inhibitory effect was not a consequence of decreased cytosolic Ca 2+. These results demonstrate that decreased cellular Ca levels are associated with decreased cytosolic Ca 2+ levels and PG synthesis, and support the hypothesis of a link between, on the one hand, cellular Ca and/or cytosolic Ca 2+ and on the other hand, PG synthesis.