ACTIVATION OF METABOTROPIC GLUTAMATE RECEPTORS INCREASES ENDOGENOUS PROTEIN-KINASE-C SUBSTRATE PHOSPHORYLATION IN ADULT HIPPOCAMPAL SLICES

We previously reported (Staak, S., Behnisch, T. and Angenstein, F., Hi ppocampal long-term potentiation: transient increase but no persistent translocation of protein kinase C (PKC) isoenzymes alpha and beta, Br ain Res., 682 (1995) 55-62) that Ca2+-dependent PKC isoenzymes alpha/b eta and gamma are not translocated between subcellular compartments af ter stimulation of glutamate receptor subtypes in hippocampal slices. Extending our previous work in this study in situ phosphorylation of e ndogenous PKC substrates and the translocation of novel PKC isoenzymes delta and epsilon was analysed to detect PKC activation. Two proteins of approximately 94 kDa and 18 kDa were first characterised to be spe cific PKC substrates. As control of the technique carbachol was shown to increase in situ phosphorylation of the two substrates without any measurable translocation of PKC protein. Activation of metabotropic gl utamate receptors by 50 mu M DHPG also increased the in situ-phosphory lation by 43.9% (94 kDa) and 32.8% (18 kDa) compared to controls but d id not induce a measurable subcellular redistribution of conventional and novel PKC isoenzymes. Stimulation by 50 mu M trans-ACPD or 0.1 mM quisqualate enhanced the in situ phosphorylation in the same range, wh ereas 0.1 mM NMDA was ineffective. To our knowledge this is the first report showing a direct link between metabotropic glutamate receptor a ctivation and increased endogenous PKC substrate phosphorylation in ad ult hippocampal slices. This PKC activation was not detectable by a re distribution of enzyme protein between subcellular compartments. We, t herefore, conclude, that the failure to detect PKC translocation in ph ysiological experiments are not an indicator for unchanged enzyme acti vity.