RT Journal Article
SR Electronic
T1 Altered Expression of G<sub>q/11</sub>α Protein Shapes mGlu1 and mGlu5 Receptor-Mediated Single Cell Inositol 1,4,5-Trisphosphate and Ca<sup>2+</sup> Signaling
JF Molecular Pharmacology
JO Mol Pharmacol
FD American Society for Pharmacology and Experimental Therapeutics
SP 174
OP 184
DO 10.1124/mol.105.014258
VO 69
IS 1
A1 Peter J. Atkinson
A1 Kenneth W. Young
A1 Steven J. Ennion
A1 James N. C. Kew
A1 Stefan R. Nahorski
A1 R. A. John Challiss
YR 2006
UL http://molpharm.aspetjournals.org/content/69/1/174.abstract
AB The metabotropic glutamate (mGlu) receptors mGlu1 and mGlu5 mediate distinct inositol 1,4,5-trisphosphate (IP3) and Ca2+ signaling patterns, governed in part by differential mechanisms of feedback regulation after activation. Single cell imaging has shown that mGlu1 receptors initiate sustained elevations in IP3 and Ca2+, which are sensitive to agonist concentration. In contrast, mGlu5 receptors are subject to cyclical PKC-dependent uncoupling and consequently mediate coincident IP3 and Ca2+ oscillations that are largely independent of agonist concentration. In this study, we investigated the contribution of Gq/11α protein expression levels in shaping mGlu1/5 receptor-mediated IP3 and Ca2+ signals, using RNA interference (RNAi). RNAi-mediated knockdown of Gq/11α almost abolished the single-cell increase in IP3 caused by mGlu1 and mGlu5 receptor activation. For the mGlu1 receptor, this unmasked baseline Ca2+ oscillations that persisted even at maximal agonist concentrations. mGlu5 receptor-activated Ca2+ oscillations were still observed but were only initiated at high agonist concentrations. Recombinant overexpression of Gqα enhanced IP3 signals after mGlu1 and mGlu5 receptor activation. It is noteworthy that although mGlu5 receptor-mediated IP3 and Ca2+ oscillations in control cells were largely insensitive to agonist concentration, increasing Gqα expression converted these oscillatory signatures to sustained plateau responses in a high proportion of cells. In addition to modulating temporal Ca2+ signals, up- or down-regulation of Gq/11α expression alters the threshold for the concentration of glutamate at which a measurable Ca2+ signal could be detected. These experiments indicate that altering Gq/11α expression levels differentially affects spatiotemporal aspects of IP3 and Ca2+ signaling mediated by the mGlu1 and mGlu5 receptors.