NMDA Induces Protein Kinase C Translocation in Guinea Pig Cerebral Synaptoneurosomes.

Abstract

ABSTRACT-N-methyl-D-aspartate (NMDA)-induced translocation of protein kinase C from the cytosol to membrane fractions was examined by the [3H]phorbol 12,13 dibutyrate (PDBu) binding method in guinea pig cerebral synaptoneurosomes. Pre treatment of synaptoneurosomes with NMDA, but not that with quisqualate or kain ate, induced changes in the distribution of [3H]PDBu binding in the cytosol and mem brane fractions in a dose-dependent manner. The NMDA-induced changes of the binding were completely dependent on Ca 2+ and inhibited by NMDA receptor anta gonists Mgt+, 2-amino-5-phosphonovaleric acid and ketamine, but not by Zn2+. Glycine slightly potentiated the NMDA-induced changes of [3H]PDBu binding. NMDA stimulated Ca 2+ uptake but not the phosphoinositide hydrolysis in the synap toneurosomes. These results suggest that NMDA enhances Ca 2+ influx through receptor-operated Ca 2+ channels, increasing intracellular calcium concentration and thereby induces translocation of protein kinase C.The excitatory amino acids, L-glutamate and L-aspartate, appear to be the major ex citatory neurotransmitters in the vertebrate central nervous system (CNS) (1). It is now well-known that there are three main recep tors for excitatory amino acids, N-methyl-D aspartate (NMDA), quisqualate and kainate receptors. Of these three receptors, NMDA receptors are concerned with various brain functions such as memory and neuronal death (2-4). Long-term potentiation (LTP), a long lasting increase in the synaptic efficacy, which is evoked by a brief high-frequency stimula tion (5), plays a crucial role in learning and memory (4). LTP, which is initially observed in the hippocampus, has now been recognized in a variety of brain structures. Induction of LTP, especially in the CA1 region of the hip pocampus, requires the activation of NMDA receptors (6), and maintenance of LTP is de pendent on the activation of protein kinase C (PKC) (7,8). Activation of NMDA receptors opens the receptor-operated Ca 2+ channels and thereby elicits a sustained Ca 2+ influx. One of the cellular events observed after Ca 2+ influx is the translocation of PKC from the cytosol to membranes, which results in a sub sequent activation of the enzyme (9, 10). Vac carino et al. (11) reported that stimulation of glutamate receptors elicits a translocation of soluble PKC into the membranes of cultured cerebellar neurons. The receptor subtypes re lated to PKC translocation seem to be a NMDA-type, because the effect is Mgt+ sensitive and blocked by novel NMDA recep tor antagonists (11).

Cellular Mechanisms of Nociceptin/Orphanin FQ (N/OFQ) Peptide (NOP) Receptor Regulation and Heterologous Regulation by N/OFQ

“…N-methyl-D-aspartate (NMDA) receptors also regulate NOP receptor function. Stimulation of the NMDA receptor promotes calcium influx and augmentation of intracellular calcium, which in turn, leads to the activation of PKC (Etoh et al, 1991). Because enhanced calcium levels are required for NOP receptor desensitization (Pu et al, 1999), short-term exposure (5 minutes) to NMDA promotes the desensitization of NOP receptor in neuronal cells.…”