THE CLONED VASOPRESSIN V1A RECEPTOR STIMULATES PHOSPHOLIPASE A(2), PHOSPHOLIPASE-C, AND PHOSPHOLIPASE-D THROUGH ACTIVATION OF RECEPTOR-OPERATED CALCIUM CHANNELS

Arginine vasopressin mediates its effects through vasopressin receptor activation and second messenger production. Recent cloning of the V1a receptor provided the opportunity to investigate the possible signal transduction pathways associated with this single vasopressin receptor subtype. When stably expressed in CHO cells, vasopressin stimulated s everal signal transduction pathways simultaneously including calcium i nflux, phospholipase A(2), phospholipase C, and phospholipase D. Vasop ressin-stimulated release of arachidonic acid, IP3 formation, and phos phatidylethanol formation (in the presence of 1% ethanol) were used as indexes of phospholipase A(2), phospholipase C, and phospholipase D a ctivation, respectively. V1a receptor-activation stimulated a peak fol lowed by a sustained plateau phase of intracellular calcium. The plate au phase was dependent on extracellular calcium, insensitive to blocke rs of voltage sensitive calcium channels, blocked by heavy metals, and quenched when MnCl2 was present in the extracellular media. Removal o f extracellular calcium blunted the release of IP3, and blocked the re lease of arachidonic acid and phosphatidylethanol indicating that thes e responses were at least in part regulated by receptor-operated calci um influx. Vasopressin-stimulated release of arachidonic acid and phos phatidylethanol were augmented with the phorbol ester PMA, and this au gmentation was blocked by inhibitors of protein kinase C and absent wi th long-term PMA treatment. Vasopressin-stimulated IP3 release was inh ibited with PMA and the inhibition reversed with protein kinase C inhi bitors.