Aim: 

Vibrio cholerae strains secrete a water soluble pore-forming toxin, the Vibrio cholerae cytolysin (VCC), responsible for lysis of several cell types in culture and indicated as a virulence factor causing diarrhoea. In order to asses relationship between VCC and ion fluxes, we studied the effect of topical exposure to VCC on epithelial parameters and paracellular permeability in isolated human colon.

Methods: 

Electrophysiological parameters and paracellular permeability of stripped human healthy colon tissues, obtained during subtotal colectomy, mounted in Ussing chamber and bathed in Krebs solution, were studied in the absence or with the addition of VCC purified from culture supernatants of V. cholerae O1 El Tor strain. Short circuit current (I_sc) and transepithelial resistance (R_t) were measured by a computerized voltage clamp system. Paracellular permeability was assessed by measuring the mucosal-to-serosal flux of fluorescein isothiocyanate (FITC).

Results: 

In 57 sigmoid colon specimens, basal I_sc and R_t were 33.7 3.1 mA/cm² and 153 10 [ohm]^.cm² respectively. Exposure to VCC 1 nM (n = 10) increased I_sc by 39.6% (p < 0.001 vs control), while R_t was reduced by 17% within 90 min. Increase in I_sc was abolished by bilateral Cl^- reduction. The contemporary presence of the anion channel blockers DIDS (1 mM, mucosal), or glybenclamide (0.1 mM, mucosal), but also of the amiloride (0.1 mM serosal), reduced by 19%, 17% and 17% respectively, the effect of VCC on the I_sc. Paracellular permeability of FITC (140 mM mucosal) (2.1·10^-6 5.5·10^-7 cm/sec; n = 4) was not significantly altered after exposure to VCC 1 nM (2.7·10^-6 8.2·10^-7 cm/sec; n = 4).

Conclusion: 

Our observations on the intact tissue model support the hypotheses that VCC forms anionic channels, which trigger an outward transcellular flux of chloride responsible for diarrhoea.