Cellular distribution of isoforms of protein kinase C (PKC) in pancreatic acini.

As in a previous study (Biochim, Biophys. Acta 1224 (1994) 127-138), we used quantitative immunoblot analysis and found that rat pancreatic acini possess four different isoforms of PKC-alpha, delta, epsilon and zeta. The phorbol ester 12-O-tetradecanoyl phorbol 13-acetate (TPA) caused translocation of each isoform from the cytosol to the membrane fraction. CCK-8 increased diacylglycerol (DAG) and caused translocation of PKC-sigma and PKC-epsilon but not that of PKC-alpha or PKC-zeta. L-364,718, a CCK receptor antagonist, prevented as well as reversed the effects of CCK-8 on DAG and on translocation of PKC-sigma and PKC-epsilon. To explore the possibility that different isoforms of PKC might have different distributions in rat pancreas, we used immunocytochemistry to determine the cellular distribution of different isoforms of PKC in intact pancreas as well as pancreatic acini. In intact pancreas, PKC-alpha and PKC-sigma were detected in islet cells but not in duct or acinar cells. PKC-epsilon was detected in the apical region of acinar cells and PKC-zeta was detected over the luminal surfaces of acinar cells and the ductules that extend from the acinus. Neither PKC-epsilon nor PKC-zeta was detected in islets. In pancreatic acini PKC-alpha and PKC-sigma were detected in islets or fragments of islets that contaminated the preparation but were not detected in acinar cells. PKC-epsilon was detected in the apical region of acinar cells and adding 1 microM TPA or 1 microM CCK-8 accentuated the immunostaining but did not alter its cellular distribution. L-364,718 reversed the changes in immunostaining caused by CCK-8. PKC-zeta was detected over the luminal surface of the acinar cells. TPA, but not CCK-8 or CCK-8 followed by L-364,718, increased the number of acini that showed staining of the luminal surfaces of acinar cells. Thus, the present results demonstrate that different isoforms of PKC are distributed differently in rat pancreas and that the different patterns of distribution can explain, at least in part, the different responses to CCK-8.