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Background: Toxin A (TcdA), toxin B (TcdB), and binary toxin (CDT) produced by Clostridium difficile (CD) are thought to play a key role in inducing diarrhea. The aim of this study was to investigate the individual and combined roles of CD toxins in inducing enterotoxic and cytotoxic effect., Methods: Ion secretion and epithelial damage were evaluated in the Ussing chambers as measure of enterotoxic or cytotoxic effect, respectively, in human-derived intestinal cells., Results: When added to the mucosal side of Caco-2 cells, TcdB, but not TcdA, induced ion secretion and its effects increased in the presence of TcdA. CDT also induced ion secretion when added to either the mucosal or serosal compartment. Serosal addition of TcdB induced epithelial damage consistent with its cytotoxic effect. However, mucosal addition of TcdB had similar effects, but only in the presence of TcdA. CDT induced epithelial damage when added to the serosal side of cell monolayers, and this was associated with a late onset but prolonged effect. All data were replicated using human colon biopsies., Conclusions: These data indicate that CD, through the combined and direct activity of its three toxins, induces integrated and synergic enterotoxic and cytotoxic effects on the intestinal epithelium.

Nutrition has a key role in the modulation of the developing intestine in early infancy, and nutrients are able to modulate several intestinal functions including nutrient absorption, ion transport, cell growth and differentiation, motility and immunomodulation. Such modulation is exerted in part through a direct interaction between a single nutrient and the enterocyte. Two functions--ion transport and cell growth--are closely connected and appear to be modulated by nutrients. This is supported by the finding that a single nutrient (e.g. zinc) stimulates ion absorption and also promotes enterocyte growth. Interestingly, intracellular signalling for either effect is similar and involves mitogen-activated protein kinase. Other nutrients also modulate enterocyte function and there is evidence that their effect may depend on their side of action (apical or basolateral) and concentration. Knowledge of the interaction between nutrients and enterocytes may be exploited to obtain clinical effects using nutrition as a long-term treatment for intestinal and non-intestinal conditions., (Copyright (c) 2010 Elsevier Ireland Ltd. All rights reserved.)

Aim: Growth hormone (GH) directly interacts with the enterocyte stimulating ion absorption and reducing ion secretion induced by agonists of cAMP. Since nitric oxide (NO) is involved in the regulation of transepithelial ion transport and acts as a second messenger for GH hemodynamic effects, we tested the hypothesis that NO may be involved in the resulting effects of GH on intestinal ion transport., Methods: Electrical parameters reflecting trans-epithelial ion transport were measured in Caco-2 cell monolayers mounted in Ussing chambers and exposed to GH and cholera toxin (CT) alone or in combination, in the presence or absence of the NO synthase (NOS) inhibitor, Nomega-nitro-L-arginine methyl ester (L-NAME). Similar experiments were conducted to determine cAMP and nitrite/nitrate concentrations. NOS expression was assayed by Western blot analysis., Results: L-NAME causes total abrogation of absorptive and anti-secretory effects by GH on intestinal ion transport. In addition, L-NAME was able to inhibit the GH-effects on intracellular cAMP concentration under basal conditions and in response to CT. GH induced a Ca(2+)-dependent increase of nitrites/nitrates production, indicating the involvement of the constitutive rather than the inducible NOS isoform, which was directly confirmed by Western blot analysis., Conclusion: These results suggest that the GH effects on intestinal ion transport, either under basal conditions or in the presence of cAMP-stimulated ion secretion, are mediated at an intracellular level by the activity of cNOS.

Background: Because zinc deficiency in malnourished children is associated with severe diarrhea, use of zinc supplementation has been proposed as an adjunct to oral rehydration. However, the effects of zinc on enterocyte ion transport are largely unknown. The objective of the present study was to investigate the effects of zinc on transepithelial ion transport under basal conditions and under conditions of enterotoxin-induced ion secretion., Methods: Ion transport was investigated by monitoring electrical parameters in human intestinal Caco-2 cells that were mounted in Ussing chambers and exposed to increasing concentrations of zinc, both in the absence and presence of either cholera toxin (CT) or Escherichia coli heat-stable enterotoxin (ST). Intracellular cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP) concentrations were also determined., Results: The addition of zinc to the luminal or basolateral side of enterocytes induced a chloride-dependent, dose-related decrease in short-circuit current, indicating ion absorption. It also resulted in a substantial reduction in CT-induced ion secretion and in cAMP concentration. E. coli ST-induced ion secretion and cGMP concentration were not affected. Ion absorption peaked at 35 mu mol/L zinc, whereas excess zinc load induced active ion secretion., Conclusions: By causing a decrease in cAMP concentration, zinc directly promotes ion absorption and substantially reduces CT-induced, but not E. coli ST-induced, ion secretion.