HIPPOCAMPAL LONG-TERM POTENTIATION - TRANSIENT INCREASE BUT NO PERSISTENT TRANSLOCATION OF PROTEIN-KINASE-C ISOENZYME-ALPHA AND ISOENZYME-BETA

Using a monoclonal antibody the translocation of the Ca2+-dependent pr otein kinase C (PKC) isoenzymes alpha/beta was studied in hippocampal slices after stimulation of glutamate receptors or induction of long-t erm potentiation. In submerged slices preincubated for 60 min in a med ium usually used in electrophysiological studies, cytosolic PKC was no t detectable and the amount of membrane-associated enzyme was increase d. The treatment of these slices with 10(-6) M phorbol-12,13-dibutyrat e induced a time-dependent translocation of alpha/beta PKC from the me mbrane-associated into the membrane-inserted state. The glutamatergic agonists N-methyl-D-aspartate, quisqualate and trans-ACPD did not caus e a membrane insertion of alpha/beta PKC as observed for the phorbol e ster when applied alone or in combination. Furthermore, 2 min and 15 m in after induction of LTP in the Schaffer collateral-CA1 pathway the d istribution of alpha/beta PKC between the two membrane fractions remai ned unchanged. An increase in the total amount of PKC immunoreactivity was measured immediately after tetanization (142.6% of controls). The data suggest that a membrane insertion of alpha/beta PKC is not a pre requisite for the LTP-induced increased phosphorylation of PKC substra tes and that the enzyme might be recruited from a previously inactive pool.