Transient translocation of protein kinase C gamma in hippocampal long-termpotentiation depends on activation of metabotropic glutamate receptors

Protein kinase C has been implicated in long-term regulation of cellular fu nctions including induction and maintenance of hippocampal long-term potent iation. In the present study the time-course of long-term potentiation-indu ced translocation of Ca2+-dependent protein kinase C isoenzymes (PKC alpha/ beta and PKC gamma) was investigated. Quantitative immunoblot analysis was used to measure translocation of these isoenzymes between cytosolic, membra ne-associated and membrane-inserted fraction at 5, 15 and 60 min after indu ction of long-term potentiation in the dentate gyrus in vivo. To investigat e the involvement of metabotropic glutamate receptors in protein kinase C r egulation during long-term potentiation induction, additional animals were treated before tetanization with (R,S)-alpha-methyl-4-carboxyphenylglycine, an antagonist of metabotropic glutamate receptors. Brief tetanic stimulati on of the perforant path resulted in a 100-150% increase in the population spike amplitude in response to test stimuli 5, 15 or 60 min after stimulati on in both untreated and (R,S)-alpha-methyl-4-carboxyphenylglycine-treated animals. Only those rats showing clear potentiation were selected for furth er biochemical analysis of the potentiated dentate gyrus. Five minutes afte r high-frequency stimulation the subcellular distribution of all studied pr otein kinase C isoenzymes was unchanged compared with controls. PKC gamma t ranslocated into the cytosol 15 min after tetanization and this redistribut ion was blocked by (R,S)-alpha-methyl-4-carboxyphenylglycine pretreatment. By contrast, PKC alpha/beta levels increased in the cytosolic fraction only 60 min after tetanization, but in a (alpha-methyl-4-carboxyphenylglycine-i ndependent manner. In an additional set of experiments it was shown that (R ,S)-alpha-methyl-4-carboxyphenylglycine alone applied intraventricularly ha d no effect on the subcellular distribution of the studied isoenzymes. The data suggest that PKC alpha/beta and PKC gamma are activated during dif ferent post-tetanic phases and metabotropic glutamate receptor activation m ight be essential for tetanus-induced translocation of postsynaptic PKC gam ma only. (C) 1999 IBRO. Published by Elsevier Science Ltd.