MODULATION OF CA2-KINASE-C IN RAT SUBMANDIBULAR ACINAR-CELLS( MOBILIZATION BY PROTEIN)

The effects of protein kinase C (PKC) activation and inhibition on the inositol 1,4,5-trisphosphate (IP3) and cytosolic Ca2+ ([Ca2+](i)) res ponses of rat submandibular acinar cells were investigated. IP3 format ion in response to acetylcholine (ACh) was not affected by the PKC act ivator phorbol 12-myristate 13-acetate (PMA), nor by the PKC inhibitor calphostin C (CaC). The ACh-elicited initial increase in [Ca2+](i) in the absence of extracellular Ca2+ was not changed by short-term (0.5 min) exposure to PMA, but significantly reduced by long-term (30 min) exposure to PMA, and also by pre-exposure to the PKC inhibitors CaC an d chelerythrine chloride (ChC). After ACh stimulation, subsequent expo sure to ionomycin caused a significantly (258%) larger [Ca2+](i) incre ase in CaC-treated cells than in control cells. However, pre-exposure to CaC For 30 min did not alter the Ca2+ release induced by ionomycin alone. These results suggest that the reduction of the initial [Ca2+]( i) increase is due to an inhibition of the Ca2+ release mechanism and not to store shrinkage. The thapsigargin (TG)-induced increase in [Ca2 +](i) was significantly reduced by short-term (0.5 min), but not by lo ng-term (30 min) exposure to PMA, nor by pre-exposure to ChC or CaC. S ubsequent exposure to ionomycin after TG resulted in a significantly ( 70%) larger [Ca2+](i) increase in PMA-treated cells than in control ce lls, suggesting that activation of PKC slows down the Ca2+ efflux or p assive leak seen in the presence of TG. Taken together, these results indicate that inhibition of PKC reduces the IP3-induced Ca2+ release a nd activation of PKC reduces the Ca2+ efflux seen after inhibition of the endoplasmic Ca2+-ATPase in submandibular acinar cells. J. Cell. Bi ochem. 72:47-55, 1999. (C) 1999 Wiley-Liss, Inc.