Dynorphin A-Mediated Reduction in Multiple Calcium Currents Involves a Goα-Subtype G Protein in Rat Primary Afferent Neurons

We examined the effect of antisera directed at specific G-protein subtype(s) on dynorphin A (Dyn A)-mediated reduction of calcium currents in rat dorsal root ganglia (DRG) neurons. Whole cell patch-clamp recordings were performed on acutely dissociated neurons. Dyn A (1 microM)-mediated decrease in calcium currents was inhibited > 90% by the preferential kappa-receptor antagonist norbinaltorphimine. Dyn A (300-1,000 nM)-mediated reduction in calcium currents was examined during intracellular administration of antisera directed against specific regions of G(o) alpha, G(i) 1 alpha/G(1) 2 alpha, and G(i) 3 alpha subunits. Intracellular dialysis with an antiserum specific for G(o) alpha for 20 min decreased calcium current inhibition by Dyn A (1 microM) in 13 of 15 neurons by an average of 75%. Dialysis with nonimmune serum did not affect Dyn A's action to reduce calcium currents. Intracellular dialysis with either anti-G(i) 1 alpha/G(i) 2 alpha or anti-G(i) 3 alpha antisera did not affect Dyn A-induced changes in calcium currents. In the presence of the N-type calcium channel antagonist omega-conotoxin GVIA, the P-type calcium channel antagonist omega-Aga IVA, and omega-Aga MVIIC applied subsequent to the other toxins, the effect of Dyn A to reduce calcium currents was inhibited by 52, 28, and 16%, respectively. The L channel antagonist nifedipine did not affect the ability to Dyn A to inhibit calcium currents. These results suggest that in rat DRG neurons coupling of kappa-opioid receptors to multiple transient, high-threshold calcium currents involves the G(o) alpha subclass of G proteins.