EVIDENCE FOR PROTEIN-KINASE-C STIMULATION IN RAT ENTEROCYTES PRETREATED WITH HEAT-STABLE ENTEROTOXIN OF ESCHERICHIA-COLI

Rat intestinal epithelial cells were isolated and the activity of the calcium- and phospholipid-dependent protein kinase C (PKC) was investi gated. The stimulation of activity by Escherichia coli heat stable ent erotoxin (STa) was about 5-fold compared to control activity (16.91+/- 1.69 vs 93.56+/-10.40 nmol/mg protein/min) and was dose dependent. Max imum enzyme activity was observed after incubation for 1 min with 6 ng of purified STa. The synergistic effects of calcium, phosphatidylseri ne and diolein on the enzyme activity were noted both in control and S Ta-treated cells. Staurosporine, a potent PKC inhibitor, significantly reduced the enzyme activity. Autoradiographic analysis of polyacrylam ide gel electrophoresis revealed that pretreatment of the cells with S Ta also resulted in the phosphorylation of specific membrane proteins each with a molecular mass of 37 kDa, 100 kDa and 140 kDa. However, ST a had no direct role on the enzyme activity. Our results, therefore, p rovide evidence for the involvement of PKC in STa-induced signal trans duction in rat enterocytes.