STa-induced translocation of protein kinase C from cytosol to membrane in rat enterocytes.

Escherichia coli heat stable enterotoxin (STa) binds to isolated rat intestinal epithelial cells and triggers a cascade reaction including increase of intracellular calcium levels ([Ca(2+)](i)) and membrane bound protein kinase C (PKC) activity. In response to STa, the cytosolic PKC activity falls from 110 to 35 nmol with increase of membrane bound PKC activity from 15 to 78 nmol. Furthermore, the increase of PKC activity induced by STa treatment was always preceded by an increase in [Ca(2+)](i). Cytosolic [Ca(2+)](i) was significantly higher (161 nM) in STa treated cells as compared to untreated cells (51.3 nM). In addition, immunoblot performed on extracts of STa treated rat enterocytes with a monoclonal antibody against PKC alpha showed a prominent band of PKC alpha. Translocation of PKC alpha could be blocked by dantrolene, a drug which inhibits the mobilisation of [Ca(2+)](i) from the intracellular store. Our results, therefore, provide evidence for the role of [Ca(2+)](i) in STa treated cells for the translocation of PKC alpha from cytosol to membrane.