Protein kinase C (PKC) has been shown to regulate epithelial Cl^- secretion in a variety of models. However, the role of PKC in duodenal mucosal bicarbonate secretion is less clear. We aimed to investigate the role of PKC in regulation of duodenal mucosal bicarbonate secretion. Bicarbonate secretion by murine duodenal mucosa was examined in vitro in Ussing chambers using a pH-stat technique. PKC isoform expression and activity were assessed by Western blotting and in vitro kinase assays, respectively. Phorbol myristate acetate (PMA, an activator of PKC) alone had no effect on duodenal bicarbonate secretion or I_sc. When PMA and dibutyryl cAMP (db-cAMP) were added simultaneously, PMA failed to alter db-cAMP-stimulated duodenal bicarbonate secretion or I_sc (P > 0.05). However, a one-hour preincubation with PMA potentiated db-cAMP-stimulated duodenal bicarbonate secretion and I_sc in a concentration-dependent manner (from 10^-8 M to 10^-5M)(P < 0.05). PMA preincubation had no effects on carbachol- or ST_a-stimulated bicarbonate secretion. Western blotting analysis revealed that PKC, , , , µ, and / were expressed in murine duodenal mucosa. Ro 318220 (an inhibitor active against PKC, , , and ), but not Go 6983 (an inhibitor active against PKC, , , and ), reversed the potentiating effect of PMA on db-cAMP-stimulated bicarbonate secretion. PMA also time- and concentration-dependently increased the activity of PKC, an effect that was prevented by Ro 318220 but not Go 6983. These results demonstrate that activation of PKC potentiates cAMP-stimulated duodenal bicarbonate secretion, whereas it does not modify basal secretion. The effect of PKC on cAMP-stimulated bicarbonate secretion is mediated by the PKC isoform.