Effects of positive allosteric modulators on single-cell oscillatory Ca2+ signaling initiated by the type 5 metabotropic glutamate receptor

Bradley, S. J. , Watson, J. M. and Challiss, R.A. J. (2009) Effects of positive allosteric modulators on single-cell oscillatory Ca2+ signaling initiated by the type 5 metabotropic glutamate receptor. Molecular Pharmacology, 76(6), pp. 1302-1313. (doi: 10.1124/mol.109.059170) (PMID:19737913) (PMCID:PMC2784724)

Abstract

Agonist stimulation of the type 5 metabotropic glutamate (mGlu5) receptor initiates robust oscillatory changes in cytosolic Ca2+ concentration ([Ca2+]i) in single cells by rapid, repeated cycles of phosphorylation/dephosphorylation of the mGlu5 receptor, involving protein kinase C and as-yet-unspecified protein phosphatase activities. An emergent property of this type of Ca2+ oscillation-generating mechanism (termed “dynamic uncoupling”) is that once a threshold concentration has been reached to initiate the Ca2+ oscillation, its frequency is largely insensitive to further increases in orthosteric agonist concentration. Here, we report the effects of positive allosteric modulators (PAMs) on the patterns of single-cell Ca2+ signaling in recombinant and native mGlu5 receptor-expressing systems. In a Chinese hamster ovary cell-line (CHO-lac-mGlu5a), none of the mGlu5 receptor PAMs studied [3,3′-difluorobenzaldazine (DFB), N-{4-chloro-2-[(1,3-dioxo-1,3-dihydro-2H-isoindol-2-yl) methyl]phenyl}-2-hydroxy-benzamide (CPPHA), 3-cyano-N-(1, 3-diphenyl-1H-prazol-5-yl)benzamide (CDPPB), S-(4-fluoro-phenyl)-{3-[3-(4-fluoro-phenyl)-[1,2,4]oxadiazol-5-yl]-piperidinl-1-yl}-methanone (ADX47273)], stimulated a Ca2+ response when applied alone, but each PAM concentration-dependently increased the frequency, without affecting the amplitude, of Ca2+ oscillations induced by glutamate or quisqualate. Therefore, PAMs can cause graded increases (and negative allosteric modulator-graded decreases) in the Ca2+ oscillation frequency stimulated by orthosteric agonist. Initial data in rat cerebrocortical astrocytes demonstrated that similar effects of PAMs could be observed in a native cell background, although at high orthosteric agonist concentrations, PAM addition could much more often be seen to drive rapid Ca2+ oscillations into peak-plateau responses. These data demonstrate that allosteric modulators can “tune” the Ca2+ oscillation frequency initiated by mGlu5 receptor activation, and this might allow pharmacological modification of the downstream processes (e.g., transcriptional regulation) that is unachievable through orthosteric ligand interactions.

• Item Type: Articles
• Status: Published
• Refereed: Yes
• Glasgow Author(s) Enlighten ID: Bradley, Dr Sophie
• Authors: Bradley, S. J., Watson, J. M., and Challiss, R.A. J.
• College/School: College of Medical Veterinary and Life Sciences > School of Molecular Biosciences
• Journal Name: Molecular Pharmacology
• Publisher: American Society for Pharmacology and Experimental Therapeutics (ASPET)
• ISSN: 0026-895X
• ISSN (Online): 1521-0111
• Published Online: 20 November 2009