Selective blockade of P/Q-type calcium channels by the metabotropic glutamate receptor type 7 involves a phospholipase C pathway in neurons.
Although presynaptic localization of mGluR7 is well established, the mechanism by which the receptor may control Ca(2+) channels in neurons is still unknown. We show here that cultured cerebellar granule cells express native metabotropic glutamate receptor type 7 (mGluR7) in neuritic processes, whereas transfected mGluR7 was also expressed in cell bodies. This allowed us to study the effect of the transfected receptor on somatic Ca(2+) channels. In transfected neurons, mGuR7 selectively inhibited P/Q-type Ca(2+) channels. The effect was mimicked by GTPgammaS and blocked by pertussis toxin (PTX) or a selective antibody raised against the G-protein alphao subunit, indicating the involvement of a G(o)-like protein. The mGuR7 effect did not display the characteristics of a direct interaction between G-protein betagamma subunits and the alpha1A Ca(2+) channel subunit, but was abolished by quenching betagamma subunits with specific intracellular peptides. Intracellular dialysis of G-protein betagamma subunits did not mimic the action of mGluR7, suggesting that both G-protein betagamma and alphao subunits were required to mediate the effect. Inhibition of phospholipase C (PLC) blocked the inhibitory action of mGluR7, suggesting that a coincident activation of PLC by the G-protein betagamma with alphao subunits was required. The Ca(2+) chelator BAPTA, as well as inhibition of either the inositol trisphosphate (IP(3)) receptor or protein kinase C (PKC) abolished the mGluR7 effect. Moreover, activation of native mGluR7 induced a PTX-dependent IP(3) formation. These results indicated that IP(3)-mediated intracellular Ca(2+) release was required for PKC-dependent inhibition of the Ca(2+) channels. Possible control of synaptic transmission by the present mechanisms is discussed.
Perroy
J
J
Centre National de la Recherche Scientifique, Unité Propre de Recherche 9023, Centre CNRS-INSERM de Pharmacologie et d'Endocrinologie, 34000 Montpellier, France.
Prezeau
L
L
De Waard
M
M
Shigemoto
R
R
Bockaert
J
J
Fagni
L
L
D000818:Animals; D000906:Antibodies / Q000494:pharmacology; D001464:Barium / Q000378:metabolism; D002121:Calcium Channel Blockers / Q000494:pharmacology; D020865:Calcium Channels, P-Type / Q000378:metabolism*; D020907:Calcium Channels, Q-Type / Q000378:metabolism*; D002478:Cells, Cultured; D002531:Cerebellum / Q000166:cytology / Q000378:metabolism; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000494:pharmacology; D020962:Heterotrimeric GTP-Binding Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism; D007424:Intracellular Fluid / Q000378:metabolism; D051379:Mice; D016501:Neurites / Q000378:metabolism; D009474:Neurons / Q000166:cytology / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D037342:Pertussis Toxin; D018094:Receptors, Metabotropic Glutamate / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects; D014162:Transfection; D010738:Type C Phospholipases / Q000378:metabolism*; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
D000906:Antibodies; D002121:Calcium Channel Blockers; D020865:Calcium Channels, P-Type; D020907:Calcium Channels, Q-Type; D018094:Receptors, Metabotropic Glutamate; D010566:Virulence Factors, Bordetella; C102719:metabotropic glutamate receptor 7; D001464:Barium; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D037342:Pertussis Toxin; D010738:Type C Phospholipases; D020962:Heterotrimeric GTP-Binding Proteins