Activation of transepithelial ion transport by secretin in human intestinal Caco-2 cells

Secretin stimulates bicarbonate secretion from pancreatic duct cells, but w hat 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 cell s grown on permeable supports for 21-28 d in a Ussing chamber and measured short-circuit currents (I-sc), Addition of secretin (5-100 nM) to the basol ateral solution dose-dependently induced biphasic increases of I,, (transie nt and sustained phase), Dibutyryl cyclic AMP (200 mu M), forskolin (10 mu M), and 3-isobutyl-1-methylxanthine (IBMX, 1 mM) also induced I,, responses similar to the administration of secretin, Addition of 5-nitro-2-(3-phenyl propylamino) benzoic acid (NPPB, 100 mu M) or benzamil (100 mu M) to the ap ical solution markedly reduced the secretin-induced I-sc increase in the tr ansient phase. A selective antagonist of cAMP-dependent protein kinase (PKA ), N-[2-(p-bromocinnamylamino)ethyl]-5-isoquinolinesulfonamide (H-89, 1 mu M), and a membrane permeable Ca2+ chelator, 1,2-bis(2-aminophenoxy)ethane-N ,N,N', N'-tetraacetic acid tetrakis(acetoxymethyl ester) (BAPTA/AM, 10 mu M ) reduced the secretin-induced I-sc. Basolateral addition of 4,4'-diisothio cyanostilbene-2,2'-disulfonic acid (DIDS, 1 mM) suppressed the sustained ph ase I-sc increase. Secretin also induced alkalinization of the apical solut ion (Delta pH, 0.053+/-0.013). The alkalinization did not occur when DIDS ( 1 mM) was added to the basolateral solution or Naf was removed from the sol utions. 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 act ivation of a DIDS-sensitive Na+-HCO3- cotransport in the basolateral membra ne of Caco-2 cells.