Oxidants potentiate Ca2+- and cAMP-stimulated Cl- secretion in intestinal epithelial T84 cells

Background & Aims: Diarrhea is one of the major complications of inflammato ry bowel disease. The role of oxidants in promoting net intestinal secretio n is important, but the cellular mechanisms underlying their effects are un clear. We examined the effects and defined the cellular actions of the oxid ant monochloramine (NH2Cl) on anion secretion in human colonic T84 cells. M ethods: Effects of NH2Cl on basal and agonist-stimulated short-circuit curr ent (Isc) of T84 monolayers were determined. Apical Cl- and basolateral Kconductances were measured by efflux of I-125(-) and Rb-86(+), respectively . Results: NH2Cl alone had little effect on Isc and I-125(-) efflux, Howeve r, pretreatment with NH2Cl led to a concentration-dependent potentiation of the Ca2+-mediated Isc and of submaximal cAMP-mediated responses. These eff ects were associated with increased basolateral K+ channel conductance and were blocked by increasing cellular Ca2+ buffering capacity with Quin-2, Wh ole-cell voltage clamp experiments showed that NH2Cl potentiated Ca2+ activ ation of basolateral K+ channel conductance. Conclusions: Oxidants potentia te both Ca2+- and cAMP-stimulated Cl- secretion by a direct effect on calci um-activated basolateral K+ channel conductance, lowering its Ca2+ activati on threshold. This effect may play an important role in amplifying and prol onging the secretory response of inflamed intestinal mucosa and enhancing t he severity of diarrhea.