51 CHOLERA TOXIN STIMULATES NA+-GLUCOSE COTRANSPORT IN A HUMAN EPITHELIAL SECRETORY CELL LINE

Abstract

Cholera toxin (CT) stimulates chloride secretion in the crypt cells with preservation of the Na+-glucose cotransport in the vlllus cells. The role of CT on the relationship between Cl secretion and glucose absorption was studied in an intestinal epithelial cell line HRT-18. Cells were studied after confluence on HAHY Milliporte filters that were mounted in Ussing chambers. Addition of 3.5 μg/ml CT to the mucosal side raised short circuit current (Isc) from 0.05 ± 0.008 to 0.32 ± 0.05 μeq.hr−1.cm−2 after 60 min which was accompanied by JC1 net secretion (-0.04 in the Ringer, to -0.33 μeq.hr−1.cm−2). Intracellular cAMP content increased from 8.98 ± 1.66 pmole/filter in Ringer solution to 19.59 ± 4.19 after CT. Addition of 10−2M glucose after CT raised the Isc further to 0.70 ± 0.08 μeq.hr−1.cm−2 by stimulating JNa net from -0.06 to +0.58 μeq.hr−1.cm−2. This additional augmentation of Isc was reversed by 0.5 mM phlorizin and was mimicked by 3.0 methyl glucose and was absent in chloride free solution. When filters were stimulated by cAMP for 15 min, Isc was also enhanced by addition of glucose. In untreated filters Isc, JNa net and JC1 net did not differ significantly before and after addition of glucose. These data indicate that the cells which secrete under the action of cholera toxin are able to express their Na+-glucose absorptive capacity. This may implicate the possibility of recruitment of an additional reserve of Na+-glucose transporters in cholera.