OPENING INTESTINAL TIGHT JUNCTIONS: A NOVEL MECHANISM OF INTESTINAL SECRETION.

Abstract

Zonula occludens toxin (Zot) is a novel toxin elaborated by Vibrio cholerae that modulates intestinal tight junctions. Aim of the study was to establish whether the permeabilizing effect of the toxin leads to intestinal secretion. Rabbit intestine was mounted in Ussing chambers and exposed to increasing concentrations of purified toxin. The tissues were also fixed, exposed to Zot, and then processed for fluorescence microscopy to determine the distribution of the toxin receptor within the intestine. Finally, purified toxin was simultaneously perfused in three distinct rabbit intestinal segments in vivo and water and electrolytes absorption measured. Zot induced a time- and dose-dependent decrease of rabbit intestinal tissue resistance in vitro starting at a toxin concentration of 1.1×10-13M. When tested in vivo, the toxin induced a jejunal secretion of water (18.2±3.8 vs -28.1±7.5 μl/min.cm, control period vs Zot-exposed period, respectively, p=0.003) and chloride (10.8±3.2 vs -2.53±0.06 μEq/min.cm, p=0.01). Similar changes were observed in the ileum (water 39.3±7.1 vs -18.7±4.8 μl/min.cm, p=0.003; chloride 9.6±1.2 vs -2.5±0.3 μEq/min.cm), but not in the colon (water 11.5.3±4.7 vs 17.5±5.0 μl/min.cm; chloride 6.0±1.3 vs 8.6±2.3 μEq/min.cm). The secretory effect of Zot in the small intestine was associated with an increased passage of polyethylene glycole 4000 in the bloodstream. Both the in vitro and in vivo effects of the toxin were reversible and paralleled the distribution of the toxin receptor within the intestine. In conclusion, the intestinal secretion induced by Zot follows the opening of tight junctions caused by the toxin and may represent a novel mechanism of intestinal secretion.