M onochloramine (NH2Cl), a granulocyte-derived reactive oxygen metabolite (ROM), increases short-circuit current (Isc) in cultured T84 monolayers in a concentration-dependent manner up to nonlethal concentrations of 75 microM. Isc increases slowly after NH2Cl, reaching a peak value of 18 +/- 2 microA/cm2 20 min after addition. The Isc changes are persistent (lasting over 20-30 min), depend on medium Cl, and are inhibitable with bumetanide. 36Cl flux studies demonstrated that NH2Cl increases serosa-to-mucosa flux of Cl without changing mucosa-to-serosa flux, consistent with stimulation of electrogenic Cl secretion. Isc responses to NH2Cl, but not PGE2, are dependent on medium calcium. As demonstrated in fura-2-loaded T84 cells, NH2Cl increases free cytosolic calcium by influx of extracellular Ca2+ and by release of Ca2+ from endogenous stores. However, NH2Cl had no effect on phosphatidylinositol metabolism or cyclic nucleotide levels. We conclude that ROM directly stimulate electrolyte secretion, an effect in part mediated by increases in cytosolic Ca2+, possibly through increasing Ca2+ permeability of cellular membranes.