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

Hydrogen peroxide (H2O2) is a reactive oxygen species that can be prod uced in the digestive tract by inflammatory cells or during reperfusio n following ischemia. To evaluate a possible direct effect of H2O2 on epithelial secretory cells, well-differentiated colonic T-84 cells wer e grown to confluence on permeable membranes and studied in Ussing cha mbers. In this model, where the measured short-circuit current (Isc) r eflects electrogenic secretion, we observed that H2O2 stimulated a con centration-dependent and transient secretory response: 5.5 mM H2O2 pro duced a peak Isc of 12.4 mu A/cm(2) after 4 min, 2.2 mM H2O2 a peak Is c 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 we re 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 c ell monolayer. This secretory response reflected transcellular chlorid e secretion because it was inhibited by the depletion of chloride in t he medium and by the suppression of the Na+,K+,2Cl(-) co-transporter a ctivity necessary for the chloride gradient driving chloride secretion . When T-84 cell monolayer resistance was studied, 5.5 mM H2O2 produce d a transient decrease in resistance, reflecting transcellular chlorid e secretion, and a gradual decline in resistance (75% of the initial v alue after 55 min). The secretory response to H2O2 was increased 2-fol d in T-84 cells maximally stimulated with 10 nM vasoactive intestinal peptide (VIP), a neuropeptide which acts via cAMP, demonstrating syner gism between the two agents. In contrast, the secretory responses prod uced 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 respons es to either VIP or carbachol were partially inhibited. These secretor y effects were specific for the oxidant properties of H2O2 because the y 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 poten tial modulator of intestinal or colonic secretion in certain pathologi c conditions such as inflammation or ischemia-reperfusion.