In CA1 pyramidal neurons of the hippocampus protein kinase C regulates calcium-dependent inactivation of NMDA receptors.
The NMDA subtype of the glutamate-gated channel exhibits a high permeability to Ca(2+). The influx of Ca(2+) through NMDA channels is limited by a rapid and Ca(2+)/calmodulin (CaM)-dependent inactivation that results from a competitive displacement of cytoskeleton-binding proteins from the NR1 subunit of the receptor by Ca(2+)/CaM (Zhang et al., 1998; Krupp et al., 1999). The C terminal of this subunit can be phosphorylated by protein kinase C (PKC) (Tingley et al., 1993). The present study sought to investigate whether PKC regulates Ca(2+)-dependent inactivation of the NMDA channel in hippocampal neurons. Activation of endogenous PKC by 4beta-phorbol 12-myristate 13-acetate enhanced peak (I(p)) and depressed steady-state (I(ss)) NMDA-evoked currents, resulting in a reduction in the ratio of these currents (I(ss)/I(p)). We demonstrated previously that PKC activity enhances I(P) via a sequential activation of the focal adhesion kinase cell adhesion kinase beta/proline-rich tyrosine kinase 2 (CAKbeta/Pyk2) and the nonreceptor tyrosine kinase Src (Huang et al., 1999; Lu et al., 1999). Here, we report that the PKC-induced depression of I(ss) is unrelated to the PKC/CAKbeta/Src-signaling pathway but depends on the concentration of extracellular Ca(2+). Intracellular applications of CaM reduced I(ss)/I(p) and occluded the Ca(2+)-dependent effect of phorbol esters on I(ss.) Moreover, increasing the concentration of intracellular Ca(2+) buffer or intracellular application of the inhibitory CaM-binding peptide (KY9) greatly reduced the phorbol ester-induced depression of I(ss). Taken together, these results suggest that PKC enhances Ca(2+)/CaM-dependent inactivation of the NMDA channel, most likely because of a phosphorylation-dependent regulation of interactions between receptor subunits, CaM, and other postsynaptic density proteins.
Lu
W Y
WY
Department of Physiology, University of Toronto, Toronto, Ontario M5S 1A8 Canada. w.lu@utoronto.ca
Jackson
M F
MF
Bai
D
D
Orser
B A
BA
MacDonald
J F
JF
D000818:Animals; D002118:Calcium / Q000494:pharmacology / Q000502:physiology*; D002147:Calmodulin / Q000502:physiology; D004533:Egtazic Acid / Q000494:pharmacology; D004789:Enzyme Activation; D005071:Evoked Potentials / Q000187:drug effects / Q000502:physiology*; D051417:Focal Adhesion Kinase 1; D051416:Focal Adhesion Protein-Tyrosine Kinases; D005998:Glycine / Q000494:pharmacology; D006624:Hippocampus / Q000502:physiology*; D066298:In Vitro Techniques; D007700:Kinetics; D016202:N-Methylaspartate / Q000494:pharmacology*; D011493:Protein Kinase C / Q000378:metabolism*; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D017966:Pyramidal Cells / Q000502:physiology*; D051381:Rats; D017208:Rats, Wistar; D016194:Receptors, N-Methyl-D-Aspartate / Q000037:antagonists & inhibitors / Q000502:physiology*; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology
D002147:Calmodulin; D016194:Receptors, N-Methyl-D-Aspartate; D004533:Egtazic Acid; D016202:N-Methylaspartate; D011505:Protein-Tyrosine Kinases; D051417:Focal Adhesion Kinase 1; D051416:Focal Adhesion Protein-Tyrosine Kinases; C496052:Ptk2 protein, rat; D011493:Protein Kinase C; D013755:Tetradecanoylphorbol Acetate; D002118:Calcium; D005998:Glycine