G-protein inhibition of phospholipase C-β1 in membranes: role of G-protein βγ subunits

Abstract

Rat liver plasma membranes reconstituted with bovine brain phospholipase C beta 1 (PLC- beta 1) exhibit a dual regulation of PLC- beta 1 activity by G-proteins. Guanosine 5'-[gamma-thio]triphosphate (GTP[S]; 0.1 nM) produced a 20-25% inhibition of PLC- beta 1 activity within 7 min of incubation. The addition of vasopressin resulted in near-basal levels of activity in the presence of 0.1 nM GTP[S]. Clonidine had little effect on the net inhibition due to GTP[S]. A similar antagonism between carbachol and GTP[S] occurred in cerebral cortical membranes containing endogenous PLC- beta 1 activity. alpha 0/i-GDP (a mixture of GDP-liganded G0 alpha and Gi alpha) attenuated the GTP[S]-dependent inhibition of PLC- beta 1 whereas alpha 0/i-GTP[S] had no effect, suggesting an involvement of G-protein beta gamma subunits in the inhibition of PLC- beta 1. Low concentrations of beta gamma subunits inhibited PLC- beta 1 activity. Inhibition was followed by reversal to basal activity and onset of stimulation as the beta gamma concentration was increased. Inhibition by beta gamma was dependent on the presence of membranes. These results indicate that G-protein beta gamma subunits constitute a mechanism by which G-protein mediate a rapid and transient inhibition of PLC- beta 1.