Translocation and Activation of Protein Kinase C in Striatal Neurons in Primary Culture: Relationship to Phorbol Dibutyrate Actions on the Inositol Phosphate Generating System and Neurotransmitter Release

Abstract: The actions of the tumor‐promoting phorbol ester phorbol dibutyrate were examined, under identical physiological conditions, on three distinct cellular processes in striatal neurons: the distribution of protein kinase C, the carbachol‐stimulated generation of [³H]inositol monophosphate, and the KCl‐evoked release of γ‐[³H]aminobutyric acid ([³H]GABA). Phorbol dibutyrate induced a rapid (complete in 5 min), dose‐dependent, entirely reversible (t_0.5= 15 min) translocation of protein kinase C from cytosol to membrane. On longer exposure to phorbol dibutyrate, membrane‐associated protein kinase C returned toward the control level, and total cellular enzyme activity declined markedly. Phorbol dibutyrate also induced the dose‐dependent attenuation of carbachol‐stimulated [³H]inositol monophosphate production and potentiation of KCl‐evoked release of [³H]GABA. The translocation of protein kinase C and the potentiation of KCl‐evoked [³H]GABA release were both rapidly reversed following washout of phorbol dibutyrate. In addition, for both processes, the effect of a 1‐h exposure to phorbol dibutyrate was markedly less than that observed following a 5‐min exposure to the agent. In direct contrast, inhibition of carbachol‐stimulated [³H]inositol monophosphate production was not rapidly reversed following washout of phorbol dibutyrate and was actually more pronounced following a 1‐h exposure, compared with a 5‐min exposure. These findings indicate that some, but not all, of the actions of phorbol dibutyrate are closely associated with the translocation of protein kinase C in striatal neurons in primary culture.