Na+/glucose cotransport in the colonic adenocarcinoma cell line HT29 cl.19A: effect of cAMP.

Abstract

The aim of the present study was to investigate the earlier finding that cAMP stimulation activates Na+/glucose cotransport in intestinal epithelia. Western blotting demonstrated the existence of Na+/glucose cotransporters in the colonic adenocarcinoma cell line HT29 cl.19A. Monolayers of this cell type showed a glucose transport, which was inhibited by 0.5 mM phlorizin (specific inhibitor of Na+/glucose cotransport). Brush border membrane vesicles of HT29 cl.19A cells exhibited a Na(+)-gradient dependent glucose transport, which was stimulated by DbcAMP-pretreatment (dibutyryladenosine 3',5'-cyclic monophosphate) of the cells. In the Ussing chamber, glucose (10 mM) unexpectedly lacked stimulatory effect on short circuit current (Isc) in HT29 cl.19A monolayers in the control situation. In DbcAMP-stimulated monolayers, glucose induced a complex Isc-response consisting of both stimulatory and inhibitory components, usually leading to a 'net' stimulation of lsc. Phlorizin (0.5 mM) did not prevent the stimulatory effect of glucose. Mannitol, alanine, fructose, ethanol (solvent for phlorizin) and the non-metabolizable glucose analogue 3-o-methyl-alpha-glucopyranoside inhibited Isc in a similar fashion as did phlorizin. Glucose transport in human colon biopsies were studied both in [14C]glucose accumulation experiments and in a specially designed Ussing chamber. There were no indications of glucose absorption in neither of these experiments. We conclude: (1) The human colon lacks Na+/glucose transport, (2) HT29 cl.19A cells exhibit Na+/glucose cotransport, which is stimulated by cAMP, (3) but this mechanism seem to be of a different type from the Na+/glucose cotransport of the 'normal' small intestine.