ON THE ROLE OF ENDOGENOUS G-PROTEIN BETA-GAMMA-SUBUNITS IN N-TYPE CA2+ CURRENT INHIBITION BY NEUROTRANSMITTERS IN RAT SYMPATHETIC NEURONS

1. Using whole-cell and perforated-patch recordings, we have examined the part played by endogenous G-protein beta gamma subunits in neurotr ansmitter-mediated inhibition of N-type Ca2+ channel current (I-Ca) in dissociated rat superior cervical sympathetic neurones. 2. Expression of the G-terminus domain of beta-adrenergic receptor kinase 1. (beta ARK1), which contains the consensus motif (QXXER) for binding G beta g amma, reduced the fast (pertussis toxin (PTX)-sensitive) and voltage-d ependent inhibition of I-Ca by noradrenaline and somatostatin, but not the slow (PTX-insensitive) and voltage-independent inhibition induced by angiotensin II. beta ARK1 peptide reduced GTP-gamma-S-induced volt age-dependent and PTX-sensitive inhibition of I-Ca but not GTP-gamma-S -mediated voltage-independent inhibition. 3. Overexpression of G beta( 1) gamma(2), which mimicked the voltage-dependent inhibition by reduci ng I-Ca density and enhancing basal facilitation, occluded the voltage -dependent noradrenaline-and somatostatin-mediated inhibitions but not the inhibition mediated by angiotensin II. 4. Go-expression of the C- terminus of beta ARK1 with beta(1) and gamma(2) subunits prevented the effects of G beta gamma dimers on basal Ca2+ channel behaviour in a m anner consistent with the sequestering of G beta gamma. 5. The express ion of the C-terminus of beta ARK1 slowed down reinhibition kinetics o f I-Ca following conditioning depolarizations and induced long-lasting facilitation by cumulatively sequestering beta gamma subunits. 6. Our findings identify endogenous G beta gamma as the mediator of the volt age-dependent, PTX-sensitive inhibition of I-Ca induced by both noradr enaline and somatostatin but not the voltage-independent, PTX-insensit ive inhibition by angiotensin II. They also support the view that volt age-dependent inhibition results from a direct G beta gamma-Ca2+ chann el interaction.