ROLE OF PROTEIN-KINASE-C IN DUODENAL MUCOSAL BICARBONATE SECRETION INTHE GUINEA-PIG

Since duodenal bicarbonate secretion (DBS) is increased by m-cholinoce ptor agonists. it was postulated that protein kinase C (PKC) has a rol e in this secretion. This premise was examined in guinea pigs, using 1 2-O-tetradecanoyl-phorbol 13-acetate (TPA) to stimulate bicarbonate pr oduction in the perfused duodenum in vivo, and to activate PKC in isol ated duodenal enterocytes. TPA (10(-7) mol . kg(-1)) infused intraveno usly stimulated active DBS from basal values of 3.64 +/- 0.66 to 8.73 +/- 1.59 mu mol . cm(-1) 10 min(-1). This effect was completely blocke d by verapamil (4 x 10(-7) mol . kg(-1)), PKC activity in duodenal ent erocytes in the basal stair was most abundant in the cytosolic fractio n (2,221 +/- 444 U/mg protein) and very low in the particulate fractio n (227 +/- 51 U/mg protein). TPA (10(-7) mol . kg(-1)) caused a time-d ependent translocation of the cytosolic, lipid-dependent activity of P KC into the particulate fraction, The effect was maximal at 5 min incu bation and was reversed by 30 min. In the particulate fraction. this a ctivity was no longer lipid-dependent, but could be stimulated by Ca2 alone. These data support the hypothesis that translocation of PKC ma y contribute to DBS.