Cyclosporin a Potentiates Receptor-Activated [Ca²⁺]_c Increase

Abstract

The use of the immunosuppressant cyclosporin A (CsA) is frequently associated with hypertension. Drug-induced local vasoconstriction appears to be responsible for this effect. Using fura-2 and ⁴⁵Ca²⁺ efflux techniques, we have examined variations in the cytosolic calcium concentration ([Ca²⁺]_c) in rat aortic smooth muscle cells and have shown that increases in [Ca²⁺]_c after [Arg⁸]vasopressin, serotonin, endothelin-1 or angiotensin II stimulation were potentiated after preincubation of cells with CsA. This effect was independent of cyclophilin or calcineurin inhibition by CsA. Measurements of inositol phosphates (InsP_n) after agonist stimulation showed that CsA also potentiated their formation. As for ⁴⁵Ca²⁺ efflux this effect was not related to cyclophilin or calcineurin inhibition. Direct stimulation of G proteins with aluminium tetrafluoride induced an increase in InsP_n formation and ⁴⁵Ca²⁺ efflux. Neither of these responses was potentiated by CsA. These results indicate that CsA acts on a target upstream of G protein activation, possibly at the receptor level, resulting in a potentiation of InsP_n formation and subsequent calcium increase.