Regulation of N-methyl-D-aspartate receptor function by constitutively active protein kinase C

The ability of the constitutively active fragment of protein kinase C (PKM) to modulate N-methyl-D-aspartate (NMDA)-activated currents in cultured mou se hippocampal neurons and acutely isolated CA1. hippocampal neurons from p ostnatal rats was studied using patch-clamp techniques. The responses of tw o heterodimeric combinations of recombinant NMDA receptors (NR1a/NR2A and N R1a/NR2B) expressed in human embryonic kidney 293 cells were also examined. Intracellular applications of PKM potentiated NMDA-evoked currents in cult ured and isolated CA1 hippocampal neurons. This potentiation was observed i n the absence or presence of extracellular Ca2+ and was prevented by the co application of the inhibitory peptide protein kinase inhibitor(19-36). Furt hermore, the PKM-induced potentiation was not a consequence of a reduction in the sensitivity of the currents to voltage-dependent blockade by extrace llular Mg2+. We also found different sensitivities of the responses of reco mbinant NMDA receptors to the intracellular application of PKM. Some potent iation was observed with the NR1a/NR2A subunits, but none was observed with the NR1a/NR2B combination. Applications of PKM to inside-out patches taken from cultured neurons increased the probability of channel opening without changing single-channel current amplitudes or channel open times. Thus, th e activation of protein kinase C is associated with potentiation of NMDA re ceptor function in hippocampal neurons largely through an increase in the p robability of channel opening.