DIFFERENTIAL ISOFORM-SPECIFIC REGULATION OF CALCIUM-INDEPENDENT PROTEIN-KINASE-C IN RAT CEREBRAL-CORTEX

Regulation of the Ca2+-independent protein kinase C (PKC) activity and isoforms by phorbol esters was investigated in rat cerebral cortex. L oss of soluble PKC eta immunoreactivity from the soluble fraction was dramatic with only a small increase in the membrane fraction. The kine tics of PKC epsilon and -delta translocation were slower than that for PKCeta, while phorbol esters had no effect on PKC zeta translocation. Despite the translocation of PKC delta, -epsilon and -eta from the so luble to the membrane fraction, both fractions showed a loss of PKC ac tivity. These data indicate that the rates of translocation, inactivat ion and/or downregulation appear to be different not only among these Ca2+-independent isozymes, but also from that reported for the Ca2+-de pendent PKCs. In addition, these results emphasize the importance of m easuring both Ca2+-independent PKC activity and immunoreactivity in ev aluating activation of these isoforms.