ENDOTHELIN MEDIATES CA INFLUX AND RELEASE IN PORCINE CORONARY SMOOTH-MUSCLE CELLS

Endothelin (ET)-induced changes in intracellular free Ca (Ca(i)) 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 (< 2.5-min duration) 70% increase in Ca(i) above baseline (n = 20). Pretreatment with diltiazem (10(-4) M; n = 10) did not change the amplitude or shape of the ET-induced Ca(i) transient. In Ca-free solution, ET elicited a Ca(i) response similar in duration but smaller (P < 0.05) in peak magnitude (31% increase; n = 7). CAF (5 x 10(-3) M) also elicited a rapid (< 60 s), transient 82% increase in Ca(i) (n = 7). In the continued presence of CAF, ET caused no change in Ca(i). In contrast, ET elicited a transient 69% increase in Ca(i) (n = 8), and in the continued presence of ET, CAF caused a 24% increase in Ca(i). Ryanodine (5 x 10(-5) M) suppressed the subsequent ET-induced Ca(i) 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 Ca(i) to baseline values in the continued presence of ET suggests the ET-sensitive store is depleted and increased Ca efflux matches Ca influx.