Gαi3primes the G protein-activated K+channels for activation by coexpressed Gβγ in intactXenopusoocytes
- 4 May 2007
- journal article
- Published by Wiley in The Journal of Physiology
- Vol. 581 (1), 17-32
- https://doi.org/10.1113/jphysiol.2006.125864
Abstract
G protein-activated K+ channels (GIRK) mediate postsynaptic inhibitory effects of neurotransmitters in the atrium and in the brain by coupling to G protein-coupled receptors (GPCRs). In neurotransmitter-dependent GIRK signalling, Gbetagamma is released from the heterotrimeric Galphabetagamma complex upon GPCR activation, activating the channel and attenuating its rectification. Now it becomes clear that Galpha is more than a mere Gbetagamma donor. We have proposed that Galphai3-GDP regulates GIRK gating, keeping its basal activity low but priming (predisposing) the channel for activation by agonist in intact cells, and by Gbetagamma in excised patches. Here we have further investigated GIRK priming by Galphai3 using a model in which the channel was activated by coexpression of Gbetagamma, and the currents were measured in intact Xenopus oocytes using the two-electrode voltage clamp technique. This method enables the bypass of GPCR activation during examination of the regulation of the channel in intact cells. Using this method, we further characterize the priming phenomenon. We tested and excluded the possibility that our estimates of priming are affected by artifacts caused by series resistance or large K+ fluxes. We demonstrate that both Galphai3 and membrane-attached Gbetagamma scavenger protein, m-phosducin, reduce the basal channel activity. However, Galphai3 allows robust channel activation by coexpressed Gbetagamma, in sharp contrast to m-phosducin, which causes a substantial reduction in the total Gbetagamma-induced current. Furthermore, Galphai3 also does not impair the Gbetagamma-dependent attenuation of the channel rectification, in contrast to m-phosducin, which prevents this Gbetagamma-induced modulation. The Galphai3-induced enhancement of direct activation of GIRK by Gbetagamma, demonstrated here for the first time in intact cells, strongly supports the hypothesis that Galphai regulates GIRK gating under physiological conditions.Keywords
This publication has 58 references indexed in Scilit:
- Pertussis-toxin-sensitive Gα subunits selectively bind to C-terminal domain of neuronal GIRK channels: evidence for a heterotrimeric G-protein-channel complexMolecular and Cellular Neuroscience, 2005
- Gαi1 and Gαi3 Differentially Interact with, and Regulate, the G Protein-activated K+ ChannelPublished by Elsevier BV ,2004
- Mapping the Gβγ-binding Sites in GIRK1 and GIRK2 Subunits of the G Protein-activated K+ ChannelPublished by Elsevier BV ,2003
- G Protein-coupled Receptors Form Stable Complexes with Inwardly Rectifying Potassium Channels and Adenylyl CyclaseJournal of Biological Chemistry, 2002
- Gαi Controls the Gating of the G Protein-Activated K+ Channel, GIRKNeuron, 2002
- The G Protein α Subunit Has a Key Role in Determining the Specificity of Coupling to, but Not the Activation of, G Protein-gated Inwardly Rectifying K+ ChannelsPublished by Elsevier BV ,2000
- The I-II Loop of the Ca 2+ Channel α 1 Subunit Contains an Endoplasmic Reticulum Retention Signal Antagonized by the β SubunitNeuron, 2000
- A G protein-gated K channel is activated via beta 2-adrenergic receptors and G beta gamma subunits in Xenopus oocytes.The Journal of general physiology, 1995
- Hyperpolarization-activated chloride currents in Xenopus oocytes.The Journal of general physiology, 1994
- Acetylcholine activation of single muscarinic K+ channels in isolated pacemaker cells of the mammalian heartNature, 1983