WE have studied the properties of the protein kinase C (PKC) subspecies that modulates the NMDA receptor (NMDAR1). The current through homomeric NMDAR1 expressed in Xenopus oocytes was increased by 200-500% by phorbol ester and also by activation of a metabotropic glutamate receptor (mGluR1) expressed in the same oocytes. This potentiation of the NMDAR1 current was not inhibited by the intracellular injection of EGTA. Intracellular injection of ε-PKC, a presynaptic PKC subspecies, potentiated the NMDAR1 current more efficiently than did the Ca2+-dependent γ-PKC, a postsynaptic subspecies of the enzyme. Our findings suggested that the presynaptic NMDA receptor could be potentiated in a Ca2+-independent manner by the activation of presynaptic PKC subspecies.
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