A pertussis/cholera toxin sensitive G-protein may mediate vasopressin-induced inositol phosphate formation in smooth muscle cell

Arg-vasopressin (AVP) stimulates the production of inositol-1,4,5-triphosphate, inositol-1,4-bisphosphate and inositol-1-phosphate in A10 smooth muscle cell line. The AVP stimulation is rapid, time and dose dependent with an ED50 value of 5 nM. Protein kinase C activator, phorbol ester blocks the AVP effect on the production of inositol phosphates, suggesting that AVP induced phospholipase C (PLC) activation is under the negative feedback regulation by diacylglycerol production. Prolonged overnight treatment with either pertussis toxin and cholera toxin resulted partial inhibition of AVP-induced production of inositol phosphates. This result suggests that a novel G-protein similar to transducin might be involved in the AVP-induced PLC activation.