BICARBONATE TRANSPORT BY RABBIT DUODENUM INVITRO - EFFECT OF VASOACTIVE INTESTINAL POLYPEPTIDE, PROSTAGLANDIN-E2, AND CYCLIC ADENOSINE-MONOPHOSPHATE

Background: Duodenal surface cells secrete bicarbonate that provides a barrier against injury. The current experiments were performed to identify duodenal bicarbonate regulatory and transport pathways. Methods: Rabbit proximal duodenal mucosa were mounted in chambers under short-circuited conditions. Bicarbonate transport, short-circuit current (Isc), and potential difference (PD) were quantitated in response to prostaglandin E2 (PGE2), vasoactive intestinal polypeptide (VIP), and dibutyryl cyclic adenosine monophosphate (db-cAMP). Anoxia (N2), 4,4′-diisothiocyanostilbene-2,2′-disulfonic acid (DIDS) and Cl-free solutions, ouabain, and Na-free solutions were also studied, as was the effect of VIP and PGE2 on duodenocyte cAMP. Results: PGE2, VIP, db-cAMP, and theophylline significantly increased bicarbonate secretion, Isc, and PD. Ouabain, Na+-free bathing solutions, and anoxia (N2) inhibited the responses. DIDS and Cl- -free solutions abolished the PGE2-induced response, reduced the response to VIP by about 50%, and had no effect on the response to db-cAMP. After PGE2 and VIP, cAMP concentration increased, yet was likely independent of bicarbonate secretion. Conclusions: Mammalian duodenal HCO3- transport requires Na+, Na+ K+-adenosine triphospatase and O2-dependent metabolic pathways and is stimulated by PGE2, VIP, and cAMP, acting by distinct pathways. © 1993.