Differential Effects of the G beta 5-RGS7 Complex on Muscarinic M3 Receptor-Induced Ca2+ Influx and Release

作者：Karpinsky Semper Darla; Volmar Claude Henry; Brothers Shaun P; Slepak Vladlen Z^*

来源：Molecular Pharmacology, 2014, 85(5): 758-768.

DOI：10.1124/mol.114.091843

The G protein beta subunit G beta 5 uniquely forms heterodimers with R7 family regulators of G protein signaling (RGS) proteins (RGS6, RGS7, RGS9, and RGS11) instead of G gamma. Although the G beta 5-RGS7 complex attenuates Ca2+ signaling mediated by the muscarinic M3 receptor (M3R), the route of Ca2+ entry (i.e., release from intracellular stores and/or influx across the plasma membrane) is unknown. Here, we show that, in addition to suppressing carbachol-stimulated Ca2+ release, G beta 5-RGS7 enhanced Ca2+ influx. This novel effect of G beta 5-RGS7 was blocked by nifedipine and 2-aminoethoxy-diphenyl borate. Experiments with pertussis toxin, an RGS domain-deficient mutant of RGS7, and UBO-QIC {L-threonine,(3R)-N-acetyl-3-hydroxy-L-leucyl-(aR)-a-hydroxybenzenepropanoyl-2,3-idehydro-N-methylalanyl-L-alanyl-N-methyl-L-alanyl-(3R)-3-[[(2S,3R)-3-hydroxy-4-methyl-1-oxo-2-[(1-oxopropyl)amino]pentyl]oxy]-L-leucyl-N,O-dimethyl-,(7 -> 1)-lactone (9CI)}, a novel inhibitor of Gq, showed that G beta 5-RGS7 modulated a Gq-mediated pathway. These studies indicate that G beta 5-RGS7, independent of RGS7 GTPase-accelerating protein activity, couples M3R to a nifedipine-sensitive Ca2+ channel. We also compared the action of G beta 5-RGS7 on M3R-induced Ca2+ influx and release elicited by different muscarinic agonists. Responses to Oxo-M [oxotremorine methiodide N,N,N,-trimethyl-4-(2-oxo-1-pyrrolidinyl)-2-butyn-1-ammonium iodide] were insensitive to G beta 5-RGS7. Pilocarpine responses consisted of a large release and modest influx components, of which the former was strongly inhibited whereas the latter was insensitive to G beta 5-RGS7. McN-A-343 [(4-hydroxy-2butynyl)-1-trimethylammonium-3-chlorocarbanilate chloride] was the only compound whose total Ca2+ response was enhanced by G beta 5-RGS7, attributed to, in part, by the relatively small Ca2+ release this partial agonist stimulated. Together, these results show that distinct agonists not only have differential M3R functional selectivity, but also confer specific sensitivity to the G beta 5-RGS7 complex.

• 出版日期2014-5