Potential mechanism of cyclosporine A-induced vascular smooth muscle contraction.

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Abstract
Arterial hypertension is a common side effect of cyclosporine A therapy; however, the cellular mechanism of cyclosporine A-induced hypertension is still unknown. The present study, therefore, examined the effect of cyclosporine A on Ca2+ kinetics and contraction in primary cultures of vascular smooth muscle cells. Cyclosporine A (10 micrograms/ml) did not affect resting intracellular free Ca2+ ([Ca2+]i) levels (151 +/- 10 vs. 146 +/- 5 nM, NS), but augmented the 10(-8) M arginine vasopressin-induced increase of [Ca2+]i (delta 76 +/- 4 vs. delta 172 +/- 6 nM, p less than 0.001). This effect of cyclosporine A was also observed in Ca2+-free medium. Arginine vasopressin-stimulated [Ca2+]i efflux within 30 seconds compared with baseline efflux rates (1,644 +/- 146 vs. 2,591 +/- 373 cpm/mg prot/30 sec, p less than 0.005), but this transient effect was significantly greater (p less than 0.001) with arginine vasopressin plus cyclosporine A (1,702 +/- 133 vs. 5,605 +/- 1235 cpm/mg prot/30 sec, p less than 0.01). Basal 45Ca2+ efflux rates were not affected by cyclosporine A, and prior incubation of the cells with cyclosporine A was required to elicit the augmentory effect. 45Ca2+ uptake was measured to examine the mechanism by which cyclosporine A may affect [Ca2+]i stores. Cyclosporine A increased Ca2+ uptake when compared with control (6.38 +/- 0.69 vs. 10.99 +/- 0.59 x 10(3) cpm/mg prot/5 min, p less than 0.001). This effect was not blocked by the Ca2+ antagonist verapamil. Arginine vasopressin (10(-8) M) induced contraction of smooth muscle cells with 25.5% of the cells responding.(ABSTRACT TRUNCATED AT 250 WORDS)