Intracellular Ca ²⁺ and Zn ²⁺ signals during monochloramine-induced oxidative stress in isolated rat colon crypts

During acute exacerbations of inflammatory bowel diseases, oxidants are generated through the interactions of bacteria in the lumen, activated granulocytes, and cells of the colon mucosa. In this study we explored the ability of one such class of oxidants, represented by monochloramine (NH ₂Cl), to serve as agonists of Ca ²⁺ and Zn ²⁺ accumulation within the colonocyte. Individual colon crypts prepared from Sprague-Dawley rats were mounted in perfusion chambers after loading with fluorescent reporters fura 2-AM and fluozin 3-AM. These reporters were characterized, in situ, for responsiveness to Ca ²⁺ and Zn ²⁺ in the cytoplasm. Responses to different concentrations of NH ₂Cl (50, 100, and 200 μM) were monitored. Subsequent studies were designed to identify the sources and mechanisms of NH ₂Cl-induced increases in Ca ²⁺ and Zn ²⁺ in the cytoplasm. Exposure to NH ₂Cl led to dose-dependent increases in intracellular Ca ²⁺ concentration ([Ca ²⁺] _i) in the range of 200-400 nM above baseline levels. Further studies indicated that NH ₂Cl-induced accumulation of Ca ²⁺ in the cytoplasm is the result of release from intracellular stores and basolateral entry of extracellular Ca ²⁺ through store-operated channels. In addition, exposure to NH ₂Cl resulted in dose-dependent and sustained increases in intracellular Zn ²⁺ concentration ([Zn ²⁺] _i) in the nanomolar range. These alterations were neutralized by dithiothreitol, which shields intracellular thiol groups from oxidation. We conclude that Ca ²⁺- and Zn ²⁺-handling proteins are susceptible to oxidation by chloramines, leading to sustained, but not necessarily toxic, increases in [Ca ²⁺] _i and [Zn ²⁺] _i. Under certain conditions, NH ₂Cl may act not as a toxin but as an agent that activates intracellular signaling pathways.