Potential involvement of calcium, CaM kinase II, and MAP kinases in PCB-stimulated insulin release from RINm5F cells

Polychlorinated biphenyls (PCBs) are environmental contaminants that induce release of insulin in rat insulinoma cells, RINm5F (Fischer et al., Life S ci. (1996) 59, 2041-2049). In the present study the mechanisms of this effe ct were investigated using noncytotoxic concentrations (10 mu g/ml) of a PC B mixture, Aroclor-1254, and the pure PCB congeners 2,2',4,4'-tetrachlorobi phenyl and 2,2',4,4',5,5'-hexachlorobiphenyl. Treatment of RINm5F cells wit h each of these agents resulted in a rapid increase in intracellular free c alcium. The presence of extracellular calcium was required for PCB-induced insulin release because removal of calcium from the medium attenuated the e ffect. In addition, pretreatment of RINm5F cells with the calcium channel b locker verapamil also blocked PCB-induced insulin release. To determine whe ther PCB-related insulin release could be associated with the enzyme, calci um/calmodulin-dependent kinase II (CaM kinase II), RINm5F cells were pretre ated with the CaM kinase II inhibitor KN-93. PCB-induced insulin release wa s completely blocked by KN-93. Under similar treatment conditions, PCBs als o induced the activity of mitogen-activated protein kinases (MAPK) 1 and 2. However, inhibition of MAPK activation by a specific inhibitor, PD-98059 ( 10.0 mu M) did not prevent insulin release induced by PCBs. The results of the present investigation suggest a role for calcium and CaM kinase II in P CB-induced insulin release. Furthermore, the results suggest that insulin r elease by PCBs is independent of the activation of MAPKs. (C) 1999 Academic Press.