Transient translocation of protein kinase Cγ in hippocampal long-term potentiation depends on activation of metabotropic glutamate receptors

Protein kinase C has been implicated in long-term regulation of cellular functions including induction and maintenance of hippocampal long-term potentiation. In the present study the time-course of long-term potentiation-induced translocation of Ca 2+-dependent protein kinase C isoenzymes (PKCα/β and PKCγ) was investigated. Quantitative immunoblot analysis was used to measure translocation of these isoenzymes between cytosolic, membrane-associated and membrane-inserted fraction at 5, 15 and 60 min after induction of long-term potentiation in the dentate gyrus in vivo. To investigate the involvement of metabotropic glutamate receptors in protein kinase C regulation during long-term potentiation induction, additional animals were treated before tetanization with ( R,S)-α-methyl-4-carboxyphenylglycine, an antagonist of metabotropic glutamate receptors. Brief tetanic stimulation 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 stimulation in both untreated and ( R,S)-α-methyl-4-carboxyphenylglycine-treated animals. Only those rats showing clear potentiation were selected for further biochemical analysis of the potentiated dentate gyrus. Five minutes after high-frequency stimulation the subcellular distribution of all studied protein kinase C isoenzymes was unchanged compared with controls. PKCγ translocated into the cytosol 15 min after tetanization and this redistribution was blocked by ( R,S)-α-methyl-4-carboxyphenylglycine pretreatment. By contrast, PKC α/β levels increased in the cytosolic fraction only 60 min after tetanization, but in a ( R,S)-α-methyl-4-carboxyphenylglycine-independent manner. In an additional set of experiments it was shown that ( R,S)-α-methyl-4-carboxyphenylglycine alone applied intraventricularly had no effect on the subcellular distribution of the studied isoenzymes. The data suggest that PKCα/β and PKCγ are activated during different post-tetanic phases and metabotropic glutamate receptor activation might be essential for tetanus-induced translocation of postsynaptic PKCγ only.