ACUTE EFFECTS OF PHORBOL ESTER AND INSULIN ON INSULIN-INDUCED GLUCOSE-UPTAKE AND PROTEIN-KINASE-C ACTIVATION IN RAT ADIPOCYTES

We examined the acute effect of pretreatment with phorbol ester and in sulin on insulin-induced glucose uptake and protein kinase C (PKC) tra nslocation from cytosol to the membrane in rat adipocytes. Adipocytes were preincubated with 1 mu M tetradecanoylphorbol 13-acetate (TPA) an d 10 nM insulin for 60 min and then stimulated with 10 nM insulin for 10 and 30 min to measure PKC activity in cytosol and membrane fraction s using a Mono Q column connected onto an HPLC system and [H-3]2-deoxy glucose (DOG) uptake, respectively. Pretreatment with 1 mu M TPA and 1 0 nM insulin for 60 min resulted in the marked decreases of insulin-in duced [H-3]2-DOG uptake. Translocation of Mono Q column-purified cytos olic PKC enzyme activity and PKC beta immunoreactivity from cytosol to the membrane was suppressed by pretreatment with TPA and insulin for 60 min. These results indicate that acute treatment with TPA and insul in which are PKC activators suppress translocation/activation of PKC, and accordingly inhibit insulin-induced glucose uptake. We suggest tha t a decrease of cytosolic PKC activity may mainly contribute to the im paired responsiveness of the glucose transport system after acute TPA and insulin treatment. (C) 1997 Elsevier Science Ireland Ltd.