Role of protein kinase c in duodenal mucosal bicarbonate secretion in the guinea pig

Since duodenal bicarbonate secretion (DBS) is increased by m-cholinoceptor agonists, it was postulated that protein kinase C (PKC) has a role in this secretion. This premise was examined in guinea pigs, using 12-O-tetradecanoyl-phorbol 13-acetate (TPA) to stimulate bicarbonate production in the perfused duodenum in vivo, and to activate PKC in isolated duodenal enterocytes. TPA (10⁻⁷ mol·kg⁻¹) infused intravenously stimulated active DBS from basal values of 3.64 ± 0.66 to 8.73 ± 1.59 μmol·cm⁻¹ 10 min⁻¹. This effect was completely blocked by verapamil (4 × 10⁻⁷ mol·kg⁻¹). PKC activity in duodenal enterocytes in the basal state was most abundant in the cytosolic fraction (2,221 ± 444 U/mg protein) and very low in the particulate fraction (227 ± 51 U/mg protein). TPA (10⁻⁷ mol·kg⁻¹) caused a time-dependent translocation of the cytosolic, lipid-dependent activity of PKC into the particulate fraction. The effect was maximal at 5 min incubation and was reversed by 30 min. In the particulate fraction, this activity was no longer lipid-dependent, but could be stimulated by Ca²⁺ alone. These data support the hypothesis that translocation of PKC may contribute to DBS.