Inhibition of a Gi-activated potassium channel (GIRK1/4) by the Gq-coupled m1 muscarinic acetylcholine receptor.
The G protein-coupled inwardly rectifying K+ channel, GIRK1/GIRK4, can be activated by receptors coupled to the Galpha(i) subunit. An opposing role for Galpha(q) receptor signaling in GIRK regulation has only recently begun to be established. We have studied the effects of m1 muscarinic acetylcholine receptor (mAChR) stimulation, which is known to mobilize calcium and activate protein kinase C (PKC) by a Galpha(q)-dependent mechanism, on whole cell GIRK1/4 currents in Xenopus oocytes. We found that stimulation of the m1 mAChR suppresses both basal and dopamine 2 receptor-activated GIRK 1/4 currents. Overexpression of Gbetagamma subunits attenuates this effect, suggesting that increased binding of Gbetagamma to the GIRK channel can effectively compete with the G(q)-mediated inhibitory signal. This G(q) signal requires the use of second messenger molecules; pharmacology implicates a role for PKC and Ca2+ responses as m1 mAChR-mediated inhibition of GIRK channels is mimicked by PMA and Ca2+ ionophore. We have analyzed a series of mutant and chimeric channels suggesting that the GIRK4 subunit is capable of responding to G(q) signals and that the resulting current inhibition does not occur via phosphorylation of a canonical PKC site on the channel itself.
Hill
J J
JJ
Department of Molecular and Cellular Biology, Harvard University, Cambridge, Massachusetts 02138, USA. jjhill@post.harvard.edu
Peralta
E G
EG
D020013:Calcium Signaling; D003001:Cloning, Molecular; D004553:Electric Conductivity; D004594:Electrophysiology / Q000379:methods; D051676:G Protein-Coupled Inwardly-Rectifying Potassium Channels; D043802:GTP-Binding Protein alpha Subunits, Gq-G11; D044387:GTP-Binding Protein beta Subunits; D044388:GTP-Binding Protein gamma Subunits; D020962:Heterotrimeric GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation; D026902:Potassium Channel Blockers; D015221:Potassium Channels / Q000235:genetics; D024661:Potassium Channels, Inwardly Rectifying; D011493:Protein Kinase C / Q000378:metabolism; D017434:Protein Structure, Tertiary; D043643:Receptor, Muscarinic M1; D011976:Receptors, Muscarinic / Q000235:genetics / Q000378:metabolism*; D011994:Recombinant Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism; D015290:Second Messenger Systems
D051676:G Protein-Coupled Inwardly-Rectifying Potassium Channels; C118981:G-protein Beta gamma; D044387:GTP-Binding Protein beta Subunits; D044388:GTP-Binding Protein gamma Subunits; D026902:Potassium Channel Blockers; D015221:Potassium Channels; D024661:Potassium Channels, Inwardly Rectifying; D043643:Receptor, Muscarinic M1; D011976:Receptors, Muscarinic; D011994:Recombinant Proteins; D011493:Protein Kinase C; D043802:GTP-Binding Protein alpha Subunits, Gq-G11; D020962:Heterotrimeric GTP-Binding Proteins