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Title

Endogenous RGS proteins enhance acute desensitization of GABA(B) receptor-activated GIRK currents in HEK-293T cells

Authors
Mutneja, Manpreet
Berton, Frederique
Suen, K. F.
Slesinger, P. A.
Published in Pflügers Archiv. 2005, vol. 450, no. 1, p. 61-73
Abstract The coupling of GABA(B) receptors to G-protein-gated inwardly rectifying potassium (GIRK) channels constitutes an important inhibitory pathway in the brain. Here, we examined the mechanism underlying desensitization of agonist-evoked currents carried by homomeric GIRK2 channels expressed in HEK-293T cells. The canonical GABA(B) receptor agonist baclofen produced GIRK2 currents that decayed by 57.3+/-1.4% after 60 s of stimulation, and then deactivated rapidly (time constant of 3.90+/-0.21 s) upon removal of agonist. Surface labeling studies revealed that GABA(B) receptors, in contrast to micro opioid receptors (MOR), did not internalize with a sustained stimulation for 10 min, excluding receptor redistribution as the primary mechanism for desensitization. Furthermore, heterologous desensitization was observed between GABA(B) receptors and MOR, implicating downstream proteins, such G-proteins or the GIRK channel. To investigate the G-protein turnover cycle, the non-hydrolyzable GTP analogue (GTPgammaS) was included in the intracellular solution and found to attenuate desensitization to 38.3+/-2.0%. The extent of desensitization was also reduced (45.3+/-1.3%) by coexpressing a mutant form of the Galphaq G-protein subunit that has been designed to sequester endogenous RGS proteins. Finally, reconstitution of GABA(B) receptors with Galphao G-proteins rendered insensitive to RGS resulted in significantly less desensitization (28.5+/-3.2%). Taken together, our results demonstrate that endogenous levels of RGS proteins effectively enhance GABA(B) receptor-dependent desensitization of GIRK currents.
Keywords Baclofen/pharmacologyCell LineG Protein-Coupled Inwardly-Rectifying Potassium ChannelsGABA Agonists/pharmacologyHumansPotassium Channels, Inwardly Rectifying/*physiologyRGS Proteins/*physiologyReceptors, GABA-B/*physiology
Stable URL http://archive-ouverte.unige.ch/unige:10369
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Other version: http://www.springerlink.com/content/yhnd0c179j6hmbp9/
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PMID: 15806402
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