Endothelin mediates Ca influx and release in porcine coronary smooth muscle cells

Endothelin (ET)-induced changes in intracellular free Ca (Cai) in freshly dispersed coronary artery smooth muscle cells were determined using fura-2 microfluorometry to differentiate the action of ET on Ca influx vs. release from internal stores. Comparison was made with caffeine (CAF)-induced Ca release from the sarcoplasmic reticulum (SR) to determine whether ET acts on the same Ca store. In physiological external solution, ET (5 x 10(-8) M) induced a rapid (within 90 s), transient (less than 2.5-min duration) 70% increase in Cai above baseline (n = 20). Pretreatment with diltiazem (10(-4) M; n = 10) did not change the amplitude or shape of the ET-induced Cai transient. In Ca-free solution, ET elicited a Cai response similar in duration but smaller (P less than 0.05) in peak magnitude (31% increase; n = 7). CAF (5 x 10(-3) M) also elicited a rapid (less than 60 s), transient 82% increase in Cai (n = 7). In the continued presence of CAF, ET caused no change in Cai. In contrast, ET elicited a transient 69% increase in Cai (n = 8), and in the continued presence of ET, CAF caused a 24% increase in Cai. Ryanodine (5 x 10(-5) M) suppressed the subsequent ET-induced Cai transient. These data on porcine cells suggest ET induces a rapid release of Ca from a CAF- and ryanodine-sensitive store and causes rapid influx of Ca, which is different from bovine smooth muscle cells. The return of Cai to baseline values in the continued presence of ET suggests the ET-sensitive store is depleted and increased Ca efflux matches Ca influx.