title: Protein kinase C activation attenuates N-methyl-D-aspartate-induced increases in intracellular calcium in cerebellar granule cells.
abstract: Activation of the N-methyl-D-aspartate (NMDA) subtype of glutamate receptor increases levels of intracellular calcium and can lead to stimulation of protein kinase C activity. Several reports have demonstrated that stimulation of protein kinase C can, in turn, increase electrophysiological responses to NMDA in certain cells or in oocytes expressing certain NMDA receptor subunits. In the present study, the effects of protein kinase C activation on NMDA receptor-mediated increases in intracellular Ca2+ level were investigated in primary cultures of rat cerebellar granule cells using fura-2 fluorescence spectroscopy. Pretreatment of the cells with the protein kinase C activator phorbol 12-myristate 13-acetate (PMA), but not the inactive analogue 4 alpha-phorbol 12-myristate 13-acetate, inhibited NMDA-induced increases in intracellular Ca2+ levels. Coincubation of cells with PMA and the kinase inhibitor staurosporine or calphostin C blocked the PMA effect. The potency of NMDA was reduced twofold, and the potency of the NMDA receptor co-agonist, glycine, to enhance the response to NMDA was decreased fourfold by pretreatment of cells with PMA. The effect on glycine was mimicked by pretreatment with okadaic acid, a protein phosphatase inhibitor. PMA treatment did not significantly alter Mg2+ inhibition of the NMDA response but decreased the potency of the competitive antagonist CGS-19755. These data suggest that, in cerebellar granule cells, the function of the NMDA receptor may be subject to feed-back inhibition by protein kinase C stimulation. Under physiological conditions, this inhibition may result from a decreased effectiveness of the endogenous co-agonists, glutamate and glycine.
authors.affiliation: Department of Pharmacology, University of Colorado Health Sciences Center, Denver 80262.
authors.forename: L D
authors.initials: LD
authors.lastname: Snell
authors.forename: K R
authors.initials: KR
authors.lastname: Iorio
authors.forename: B
authors.initials: B
authors.lastname: Tabakoff
authors.forename: P L
authors.initials: PL
authors.lastname: Hoffman
mesh_terms: D000470:Alkaloids / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002478:Cells, Cultured; D002531:Cerebellum / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D004789:Enzyme Activation; D005998:Glycine / Q000494:pharmacology; D007424:Intracellular Fluid / Q000378:metabolism; D007700:Kinetics; D008278:Magnesium Sulfate / Q000494:pharmacology; D016202:N-Methylaspartate / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D009281:Naphthalenes; D009474:Neurons / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D010875:Pipecolic Acids / Q000494:pharmacology; D011083:Polycyclic Compounds / Q000494:pharmacology; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D016194:Receptors, N-Methyl-D-Aspartate / Q000037:antagonists & inhibitors / Q000502:physiology*; D019311:Staurosporine; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology*
chemical_list: D000470:Alkaloids; D009281:Naphthalenes; D010875:Pipecolic Acids; D011083:Polycyclic Compounds; D016194:Receptors, N-Methyl-D-Aspartate; C053672:selfotel; D016202:N-Methylaspartate; D008278:Magnesium Sulfate; D011493:Protein Kinase C; D019311:Staurosporine; C058819:calphostin C; D013755:Tetradecanoylphorbol Acetate; D002118:Calcium; D005998:Glycine