title: Stimulation of insulin release by the phorbol ester 12-O-tetradecanoylphorbol 13-acetate in the clonal cell line RINm5F despite a lowering of the free cytoplasmic Ca2+ concentration.
abstract: The effects of 12-O-tetradecanoylphorbol 13-acetate (TPA) on the handling of Ca2+ and insulin release were investigated in the clonal insulin-producing cell line RINm5F. The presence of the phorbol ester lowered the free cytoplasmic Ca2+ and suppressed the increase obtained by depolarization with high concentrations of K+. Despite the lowering in cytoplasmic Ca2+ by TPA, there was a concomitant stimulation of insulin release indicating that one feature of protein kinase C activation is to make the secretory system more sensitive to Ca2+. Furthermore, there was no interaction of TPA with the mechanisms responsible for inositol 1,4,5-tris(phosphate) induced Ca2+ release or Ca2+ uptake in permeabilized cells. Although TPA slightly depolarized the RINm5F cells there was no interference with K+-induced depolarization. It is suggested that an additional effect of protein kinase C activation in these cells, is to stimulate the extrusion of Ca2+ over the plasma membrane.
mesh_terms: D000818:Animals; D002118:Calcium / Q000502:physiology*; D002460:Cell Line; D003593:Cytoplasm / Q000378:metabolism; D007295:Inositol Phosphates / Q000378:metabolism; D007328:Insulin / Q000378:metabolism*; D000078790:Insulin Secretion; D008564:Membrane Potentials / Q000187:drug effects; D010704:Phorbols / Q000494:pharmacology*; D011493:Protein Kinase C / Q000378:metabolism; D051381:Rats; D012636:Secretory Rate / Q000187:drug effects; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology*
chemical_list: D007295:Inositol Phosphates; D007328:Insulin; D010704:Phorbols; D011493:Protein Kinase C; D013755:Tetradecanoylphorbol Acetate; D002118:Calcium