NDLI: Gαi3 primes the G protein-activated K+ channels for activation by coexpressed Gβγ in intact Xenopus oocytes

Content Provider	PubMed Central
Author	Rubinstein, Moran Peleg, Sagit Berlin, Shai Brass, Dovrat Dascal, Nathan
Copyright Year	2007
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, Gβγ is released from the heterotrimeric Gαβγ complex upon GPCR activation, activating the channel and attenuating its rectification. Now it becomes clear that Gα is more than a mere Gβγ donor. We have proposed that Gαi3–GDP regulates GIRK gating, keeping its basal activity low but priming (predisposing) the channel for activation by agonist in intact cells, and by Gβγ in excised patches. Here we have further investigated GIRK priming by Gαi3 using a model in which the channel was activated by coexpression of Gβγ, 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 Gαi3 and membrane-attached Gβγ scavenger protein, m-phosducin, reduce the basal channel activity. However, Gαi3 allows robust channel activation by coexpressed Gβγ, in sharp contrast to m-phosducin, which causes a substantial reduction in the total Gβγ-induced current. Furthermore, Gαi3 also does not impair the Gβγ-dependent attenuation of the channel rectification, in contrast to m-phosducin, which prevents this Gβγ-induced modulation. The Gαi3-induced enhancement of direct activation of GIRK by Gβγ, demonstrated here for the first time in intact cells, strongly supports the hypothesis that Gαi regulates GIRK gating under physiological conditions.
Related Links	http://dx.doi.org/10.1113/jphysiol.2006.125864
Ending Page	32
Page Count	16
Starting Page	17
File Format	PDF
ISSN	00223751
e-ISSN	14697793
Journal	The Journal of Physiology
Issue Number	Pt 1
Volume Number	581
Language	English
Publisher	Blackwell Science Inc
Publisher Date	2007-05-15
Access Restriction	Open
Rights Holder	Blackwell Science Inc
Subject Keyword	Physiology Research in Higher Education
Content Type	Text
Resource Type	Article
Subject	Physiology Sports Science

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