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Am J Physiol Gastrointest Liver Physiol 286: G814-G821, 2004. First published January 8, 2004; doi:10.1152/ajpgi.00251.2003
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HORMONES AND SIGNALING

Protein kinase C potentiates cAMP-stimulated mouse duodenal mucosal bicarbonate secretion in vitro

Bi-Guang Tuo, Jimmy Y. C. Chow, Kim E. Barrett, and Jon I. Isenberg{dagger}

Division of Gastroenterology, Department of Medicine, University of California, San Diego, School of Medicine, San Diego, California 92103-8413

Submitted 3 June 2003 ; accepted in final form 22 December 2003

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. PMA (an activator of PKC) alone had no effect on duodenal bicarbonate secretion or short-circuit current (Isc). When PMA and dibutyryl-cAMP (db-cAMP) were added simultaneously, PMA failed to alter db-cAMP-stimulated duodenal bicarbonate secretion or Isc (P > 0.05). However, a 1-h preincubation with PMA potentiated db-cAMP-stimulated duodenal bicarbonate secretion and Isc in a concentration-dependent manner (from 10-8 to 10-5M) (P < 0.05). PMA preincubation had no effects on carbachol- or heat-stable toxin-stimulated bicarbonate secretion. Western blot analysis revealed that PKC{alpha}, -{gamma}, -{epsilon}, -{theta}, -µ, and -{iota}/{lambda} were expressed in murine duodenal mucosa. Ro 31–8220 (an inhibitor active against PKC{epsilon}, -{alpha}, -{beta}, and -{gamma}), but not Gö 6983 (an inhibitor active against PKC{alpha}, -{gamma}, -{beta}, and -{delta}), reversed the potentiating effect of PMA on db-cAMP-stimulated bicarbonate secretion. PMA also time- and concentration-dependently increased the activity of PKC{epsilon}, an effect that was prevented by Ro 31–8220 but not Gö 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{epsilon} isoform.

protein kinase C{epsilon}; bicarbonate secretion; phorbol 12-myristate 13-acetate; adenosine 3',5'-cyclic monophosphate


Address for reprint requests and other correspondence: K. E. Barrett, Univ. of California, San Diego Medical Center, Div. of Gastroenterology, 8414, 200 W. Arbor Dr., San Diego, CA 92103-8413 (E-mail: kbarrett{at}ucsd.edu).




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