Stimulation of specific GTPase activity by vasopressin in isolated membranes from cultured rat hepatocytes.

Membranes were isolated by isotonic homogenization and differential centrifugation from rat hepatocytes cultured overnight. The specific GTPase activity of the membranes was 1-1.3 pmol gamma-labelled GTP hydrolysed/mg protein per min in the presence of 1.2 mM Na+, 2 mM EGTA, 1 mM ATP and 0.2 mM 5-adenylyl imidodiphosphate. Under these conditions there was a stimulation of specific GTPase activity of no more than 20% by 11-115 nM vasopressin. No effect of vasopressin was seen in the presence of 1.7 microM free Ca2+ or 100 mM Na+. The findings indicate that vasopressin is able to influence GTPase activity as well as accelerate phosphoinositide breakdown in rat hepatocytes.