DYNORPHIN A-MEDIATED REDUCTION IN MULTIPLE CALCIUM CURRENTS INVOLVES A G(0-ALPHA)-SUBTYPE G-PROTEIN IN RAT PRIMARY AFFERENT NEURONS

We examined the effect of antisera directed at specific G-protein subt ype(s) on dynorphin A (Dyn A)-mediated reduction of calcium currents i n rat dorsal root ganglia (DRG) neurons. Whole cell patch-clamp record ings were performed on acutely dissociated neurons. Dyn A (1 mu M)-med iated decrease in calcium currents was inhibited >90% by the preferent ial kappa-receptor antagonist norbinaltorphimine. Dyn A(300-1,000 nM)- mediated reduction in calcium currents was examined during intracellul ar administration of antisera directed against specific regions of G(0 alpha), G(i1 alpha)/G(i2 alpha), and G(i3 alpha) subunits. Intracellu lar dialysis with an antiserum specific for G(0) alpha for 20 min decr eased calcium current inhibition by Dyn A (1 mu M) in 13 of 15 neurons by an average of 75%. Dialysis with nonimmune serum did not affect Dy n A's action to reduce calcium currents. Intracellular dialysis with e ither anti-G(i1 alpha)/G(i2 alpha) or anti-G(i3 alpha) antisera did no t affect Dyn A-induced changes in calcium currents. In the presence of the N-type calcium channel antagonist omega-conotoxin GVIA, the P-typ e calcium channel antagonist omega-Aga IVA, and omega-Aga MVIIC applie d subsequent to the other toxins, the effect of Dyn A to reduce calciu m currents was inhibited by 52, 28, and 16%, respectively. The L chann el antagonist nifedipine did not affect the ability of Dyn A to inhibi t calcium currents. These results suggest that in rat DRG neurons coup ling of kappa-opioid receptors to multiple transient, high-threshold c alcium currents involves the G(0 alpha) subclass of G proteins.