MODULATION OF HUMAN COLONIC T-84 CELL SECRETION BY HYDROGEN-PEROXIDE

Hydrogen peroxide (H2O2) is a reactive oxygen species that can be produced in the digestive tract by inflammatory cells or during reperfusion following ischemia. To evaluate a possible direct effect of H2O2 on epithelial secretory cells, well-differentiated colonic T-84 cells were grown to confluence on permeable membranes and studied in Ussing chambers. In this model, where the measured short-circuit current (Isc) reflects electrogenic secretion, we observed that H2O2 stimulated a concentration-dependent and transient secretory response: 5.5 mM H2O2 produced a peak Isc of 12.4 mu A/cm(2) after 4 min, 2.2 mM H2O2 a peak Isc of 7.9 mu A/cm(2) after 4 min, and 1.1 mM H2O2 a peak Isc of 5.5 mu A/cm(2) after 16 min (N = 5). When 97 experiments using 5.5 mM H2O2 were reviewed, the mean peak Isc response was 8.9 +/- 0.5 mu A/cm(2). A similar secretory response was elicited whether H2O2 was added to the serosal, to the mucosal, or simultaneously to both sides of the T-84 cell monolayer. This secretory response reflected transcellular chloride secretion because it was inhibited by the depletion of chloride in the medium and by the suppression of the Na+,K+,2Cl(-) co-transporter activity necessary for the chloride gradient driving chloride secretion. When T-84 cell monolayer resistance was studied, 5.5 mM H2O2 produced a transient decrease in resistance, reflecting transcellular chloride secretion, and a gradual decline in resistance (75% of the initial value after 55 min). The secretory response to H2O2 was increased 2-fold in T-84 cells maximally stimulated with 10 nM vasoactive intestinal peptide (VIP), a neuropeptide which acts via cAMP, demonstrating synergism between the two agents. In contrast, the secretory responses produced by H2O2 and carbachol, which acts through the Ca2+ pathway, were additive. A late inhibitory effect of H2O2 was also observed: in cells previously treated with 5.5 mM H2O2, the subsequent secretory responses to either VIP or carbachol were partially inhibited. These secretory effects were specific for the oxidant properties of H2O2 because they were inhibited by 450 U/mL catalase and by 5 mM dithiothreitol, but were unaffected by 50 mu M deferoxamine B or Fe3+. H2O2 may be a potential modulator of intestinal or colonic secretion in certain pathologic conditions such as inflammation or ischemia-reperfusion.