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Original Article

Endogenous Regulator of G-Protein Signaling Proteins Regulate the Kinetics of G_q/11-Mediated Modulation of Ion Channels in Central Nervous System Neurons

Department of Pharmacology and Toxicology, Medical College of Georgia, Augusta, Georgia

Abstract

Slow synaptic potentials are generated when metabotropic G-protein-coupled receptors activate heterotrimeric G-proteins, which in turn modulate ion channels. Many neurons generate excitatory postsynaptic potentials mediated by G-proteins of the G_q/11 family, which in turn activate phospholipase C-. Accessory GTPase-activating proteins (GAPs) are thought to be required to accelerate GTP hydrolysis and rapidly turn off G-proteins, but the involvement of GAPs in neuronal G_q/11 signaling has not been examined. Here, we show that regulator of G-protein signaling (RGS) proteins provide necessary GAP activity at neuronal G_q/11 subunits. We reconstituted inhibition of native 2-pore domain potassium channels in cerebellar granule neurons by expressing chimeric G subunits that are activated by G_i/o-coupled receptors, thus bypassing endogenous G_q/11 subunits. RGS-insensitive variants of these chimeras mediated inhibition of potassium channels that developed and recovered more slowly than inhibition mediated by RGS-sensitive (wild-type) chimeras or native G_q/11 subunits. These changes were not accompanied by a change in agonist sensitivity, as might be expected if RGS proteins acted primarily as effector antagonists. The slowed recovery from potassium channel inhibition was largely reversed by an additional mutation that mimics the RGS-bound state. These results suggest that endogenous RGS proteins regulate the kinetics of rapid G_q/11-mediated signals in central nervous system neurons by providing GAP activity.

Address correspondence to: Dr. Nevin Lambert, Department of Pharmacology and Toxicology, Medical College of Georgia, Augusta, GA 30912-2300. E-mail: nlambert{at}mcg.edu