STIMULATORY EFFECTS OF PROTEIN-KINASE-C AND CALMODULIN KINASE-II ON N-METHYL-D-ASPARTATE RECEPTOR CHANNELS IN THE POSTSYNAPTIC DENSITY OF RAT-BRAIN

To clarify the regulatory mechanism of the N-methyl-D-aspartate (NMDA) receptor/channel by several protein kinases, we examined the effects of purified type II of protein kinase C (PKC-II), endogenous Ca2+/calmodulin-dependent protein kinase II (CaMK-II), and purified cyclic AMP-dependent protein kinase on NMDA receptor/channel activity in the postsynaptic density (PSD) of rat brain. Purified PKC-II and endogenous CaMK-II catalyzed the phosphorylation of 80-200-kDa proteins in the PSD and L-glutamate- (or NMDA)-induced increase of (+)-5-[H-3]methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5, 10-imine maleate ([H-3]MK-801; open channel blocker for NMDA receptor/channel) binding activity was significantly enhanced. However, the pretreatment of PKC-II- and CaMK-II-catalyzed phosphorylation did not change the binding activity Of L-[H-3]glutamate, cis-4-[H-3](phospho-nomethyl)piperidine-2-carboxylate ([H-3]CGS-19755; competitive NMDA receptor antagonist), [H-3]glycine, alpha-[H-3]-amino-3-hydroxy-5-methyl-isoxazole-4-propionate, or [H-3]-kainate in the PSD. Pretreatment with PKC-II- and CaMK-II-catalyzed phosphorylation enhanced L-glutamate-induced increase of [H-3]MK-801 binding additionally, although purified cyclic AMP-dependent protein kinase did not change L-glutamate-induced [H-3]MK-801 binding. From these results, it is suggested that PKC-II and/or CaMK-II appears to induce the phosphorylation of the channel domain of the NMDA receptor/channel in the PSD and then cause an enhancement of Ca2+ influx through the channel.