Effect of protein kinase C activation and Ca2+ mobilization on hexose transport in Swiss 3T3 cells

Down-modulation of Ca2+-activated, phospholipid-dependent protein kinase (protein binase C), which was accomplished by pretreatment with phorbol-12,13-dibutyrate for 24 h, resulted in the loss of a phorbol ester-induced stimulation of hexose transport activity in Swiss 3T3 cells. In these cells, however, platelet-derived growth factor as well as Ca2+ ionophore A23187 were still able to induce stimulation of hexose transport activity accompanied by the elevation of intracellular free Ca2+ concentration. Since chelation of extracellular Ca2+ inhibited this stimulation, inflow of extracellular Ca2+ into cytoplasm seemed to be essential for the stimulatory effect of platelet-derived growth factor and A23187 on hexose transport. Epidermal growth factor and insulin also stimulated hexose transport activity regardless of the absence of protein kinase C. However, in the case of epidermal growth factor, intracellular Ca2+, but not extracellular Ca2+, was found to be necessary for the stimulation. On the other hand, insulin stimulated the hexose transport independent of both intra- and extracellular Ca2+.