Oxidants potentiate Ca(2+)- and cAMP-stimulated Cl(-) secretion in intestinal epithelial T84 cells.

Background & Aims: Diarrhea is one of the major complications of inflammatory bowel disease. The role of oxidants in promoting net intestinal secretion is important, but the cellular mechanisms underlying their effects are unclear. We examined the effects and defined the cellular actions of the oxidant monochloramine (NH(2)Cl) on anion secretion in human colonic T84 cells.
Methods: Effects of NH(2)Cl on basal and agonist-stimulated short-circuit current (Isc) of T84 monolayers were determined. Apical Cl(-) and basolateral K(+) conductances were measured by efflux of (125)I(-) and (86)Rb(+), respectively.
Results: NH(2)Cl alone had little effect on Isc and (125)I(-) efflux. However, pretreatment with NH(2)Cl led to a concentration-dependent potentiation of the Ca(2+)-mediated Isc and of submaximal cAMP-mediated responses. These effects were associated with increased basolateral K(+) channel conductance and were blocked by increasing cellular Ca(2+) buffering capacity with Quin-2. Whole-cell voltage clamp experiments showed that NH(2)Cl potentiated Ca(2+) activation of basolateral K(+) channel conductance.
Conclusions: Oxidants potentiate both Ca(2+)- and cAMP-stimulated Cl(-) secretion by a direct effect on calcium-activated basolateral K(+) channel conductance, lowering its Ca(2+) activation threshold. This effect may play an important role in amplifying and prolonging the secretory response of inflamed intestinal mucosa and enhancing the severity of diarrhea.