The protein kinase C, calcium-independent and calcium-dependent kinase activities of glial cells in primary culture and subculture

The activity of calcium-independent, calcium-dependent and calcium + phospholipid-dependent (protein kinase C) kinases in cytosol fractions from rat brain glial cells in primary culture and from subcultured astrocytes and in oligodendrocyte-type 2 astrocyte lineage glia has been measured with histone Type IIIS as substrate. Accurate measurement of protein kinase C activity was achieved only after chromatography of glial cytosols on DE-52 anion exchange columns to remove an endogenous inhibitor, identified tentatively as a phosphatase possibly of the protein phosphatase 2A class. The specific activity of protein kinase C in glial cell cytosol increased from 7.5 ± 0.8 to 37.9 ± 0.9 nmol 32P incorporated/mg protein/10 min with increasing culture age. Protein kinase C activity in glial cytosol was significantly higher when primary cultures were grown in a defined medium lacking serum. Astrocyte-conditioned medium and phorbol esters caused a rapid translocation of glial cell protein kinase C activity from cytosol to membrane compartments. Myelin basic protein and protamine have been compared with histone as substrates for measurement of calcium-independent, calcium-dependent and calcium + phospholipid-dependent kinase activities in glial cytosol.