Abstract
Secretin stimulates bicarbonate secretion from pancreatic duct cells, but what influence secretin exerts on intestinal tissues remains to be clarified. The aim of this study is to examine effects of secretin on ion transport in intestinal epithelial Caco-2 cells. We mounted monolayers of Caco-2 cells grown on permeable supports for 21–28 d in a Ussing chamber and measured short-circuit currents (Isc). Addition of secretin (5–100 nM) to the basolateral solution dose-dependently induced biphasic increases of Isc (transient and sustained phase). Dibutyryl cyclic AMP (200 μM), forskolin (10 μM), and 3-isobutyl-1-methylxanthine (IBMX, 1 mM) also induced Isc responses similar to the administration of secretin. Addition of 5-nitro-2-(3-phenylpropylamino) benzoic acid (NPPB, 100 μM) or benzamil (100 μM) to the apical solution markedly reduced the secretin-induced Isc increase in the transient phase. A selective antagonist of cAMP-dependent protein kinase (PKA), N-[2-(p-bromocinnamylamino)ethyl]-5-isoquinolinesulfonamide (H-89, 1 μM), and a membrane permeable Ca2+ chelator, 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid tetrakis(acetoxymethyl ester) (BAPTA/AM, 10 μM) reduced the secretin-induced Isc. Basolateral addition of 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS, 1 mM) suppressed the sustained phase Isc increase. Secretin also induced alkalinization of the apical solution (ΔpH, 0.053 ± 0.013). The alkalinization did not occur when DIDS (1 mM) was added to the basolateral solution or Na+ was removed from the solutions. Taken together, our observations suggest: (1) secretin stimulates a benzamil-sensitive Na+ influx and an NPPB-sensitive Cl− efflux across the apical membrane through PKA-dependent and Ca2+-sensitive pathways; and (2) secretin also induces alkalinization of the apical solution through the activation of a DIDS-sensitive Na+-HCO3− cotransport in the basolateral membrane of Caco-2 cells.
