Regulators of G-Protein Signaling (RGS) Proteins Promote Receptor Coupling to G-Protein-Coupled Inwardly Rectifying Potassium (GIRK) Channels

Regulators of G-protein signaling (RGS) proteins negatively modulate presynaptic mu-opioid receptor inhibition of GABA release in the ventrolateral periaqueductal gray (vIPAG). Paradoxically, we find that G-protein-coupled receptor (GPCR) activation of G-protein-gated inwardly rectifying K+ channels (GIRKs) in the v1PAG is reduced in an agonist- and receptor-dependent manner in transgenic knock-in mice of either sex expressing mutant RGS-insensitive Gao proteins. mu-Opioid receptor agonist activation of GIRK currents was reduced for DAMGO and fentanyl but not for [Met(5)]-enkephalin acetate salt hydrate (ME) in the RGS-insensitive heterozygous (Het) mice compared with wild-type mice. The GABA(B) agonist baclofen-induced GIRK currents were also reduced in the Het mice. We confirmed the role of G alpha o proteins in mu-opioid receptor and GABA(B) receptor signaling pathways in wild-type mice using myristoylated peptide inhibitors of G alpha o(1), and G alpha i(1-3) . The results using these inhibitors indicate that receptor activation of GIRK channels is dependent on the preference of the agonist-stimulated receptor for G alpha o versus that for G alpha i. DAMGO and fentanyl-mediated GIRK currents were reduced in the presence of the G alpha o, inhibitor, but not the G alpha i(1-3) inhibitors. In contrast, the G alpha o, peptide inhibitor did not affect ME activation of GIRK currents, which is consistent with results in the Het mice, but the G alpha i(1-3) inhibitors significantly reduced ME-mediated GIRK currents. Finally, the reduction in GIRK activation in the Het mice plays a role in opioid- and baclofen-mediated spinal antinociception, but not supraspinal antinociception. Thus, our studies indicate that RGS proteins have multiple mechanisms of modulating GPCR signaling that produce negative and positive regulation of signaling depending on the effector.