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Gα i3 primes the G protein‐activated K + channels for activation by coexpressed Gβγ in intact Xenopus oocytes
Author(s) -
Rubinstein Moran,
Peleg Sagit,
Berlin Shai,
Brass Dovrat,
Dascal Nathan
Publication year - 2007
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.2006.125864
Subject(s) - g protein coupled inwardly rectifying potassium channel , xenopus , heterotrimeric g protein , g protein , g protein coupled receptor , biophysics , microbiology and biotechnology , voltage clamp , priming (agriculture) , patch clamp , chemistry , biology , neuroscience , receptor , membrane potential , biochemistry , signal transduction , germination , botany , gene
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 Gα i3 –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 Gα i3 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 Gα i3 and membrane‐attached Gβγ scavenger protein, m‐phosducin, reduce the basal channel activity. However, Gα i3 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, Gα i3 also does not impair the Gβγ‐dependent attenuation of the channel rectification, in contrast to m‐phosducin, which prevents this Gβγ‐induced modulation. The Gα i3 ‐induced enhancement of direct activation of GIRK by Gβγ, demonstrated here for the first time in intact cells, strongly supports the hypothesis that Gα i regulates GIRK gating under physiological conditions.