Receptor influences in GIRK current activation and desensitization

G protein-coupled receptors (GPCRs) are seven-transmembrane domain receptors that sense extracellular signal and activate intracellular signaling pathways. Metabotropic glutamate receptor 2 (mGluR2) is one of the GPCRs coupled to Gi/o proteins whose Gβγ subunits stimulate G protein-gated inwardly rectifying K+ channels (GIRKs). Previous experiments demonstrated that in planar lipid bilayer both active forms of G proteins [Gα (GTPγS-stimulated) and Gβγ subunits] were required to activate GIRK channels in the absence of the receptor, but surprisingly, the Gβγ subunit alone could activate GIRK channel in the presence of GPCR. Currently, it is not clear whether GPCRs play a role beyond catalyzing the dissociation of Gα and Gβγ subunits in the presence of extracellular agonist and intracellular GTP. Here we compare the G protein-stimulated GIRK currents in the presence and absence of mGluR2 by performing whole-cell patch clamp recordings on two types of cells: a HEK293 cell line stably expressing GIRK channels (HEK/GIRK) and HEK/GIRK cells with mGluR2 expressed transiently. Our experiments revealed that mGluR2 affects the behavior of G proteins even in the absence of the agonist. We show that intracellular application of GTP activated GIRK currents, and the GTP-induced GIRK currents became greater in the presence mGluR2. We also show that desensitization kinetics of the GTP-stimulated GIRK currents became greater and faster in the presence of mGluR2