ENDOTHELIN-1 AND INSULIN ACTIVATE THE STEADY-STATE VOLTAGE-DEPENDENT R-TYPE CA2-MUSCLE CELLS VIA A PERTUSSIS TOXIN AND CHOLERA-TOXIN SENSITIVE G-PROTEIN( CHANNEL IN AORTIC SMOOTH)

In single rabbit aortic smooth muscle cells, and at a concentration kn own to induce a maximum sustained increase of intracellular Ca2+ via a ctivation of the steady-state voltage dependent R-type Ca2+ channels, endothelin-1 (10(-7) M) and insulin (80 mu U/ml) were found to induce a sustained increase in cytosolic free Ca2+ ([Ca](i)) levels that was significantly attenuated by pre-treatment with either pertussis toxin (PTX), cholera toxin (CTX) or removal of extracellular Ca2+. However, both PTX and CTX failed to inhibit the sustained depolarization-evoked sustained Ca2+ influx and [Ca](i) elevation via activation of the R-t ype Ca2+ channels. Moreover, ET-1 and insulin-evoked sustained increas es in Ca2+ influx were not attenuated by the selective PKC inhibitor, bisindolylmaleimide (BIS), or the specific L-type Ca2+ channel blocker , nifedipine, but were completely reversed by the R-type Ca2+ channel blocker, (-) PN 200-110 (isradipine). These data suggest that both ins ulin and ET-1 activate the nifedipine-insensitive but isradipine-sensi tive steady state voltage dependent R-type Ca2+ channels present on ra bbit VSMCs and these channels are directly coupled to PTX and CTX sens itive G protein(s).