Effect of melatonin on chloride secretion by human colonic T84 cells

Abstract

The effect of melatonin on human colonic T84 cells was studied using the short-circuit current (I(SC)) technique. Basolateral, as well as apical, addition of melatonin stimulated I(SC) in a concentration-dependent manner (EC 50 at about 100 μM). The I(SC) response to melatonin was nearly abolished when external Cl - was removed. The increase in I(SC) was also blocked by apical addition of two Cl - channel blockers, 4,4'-diisothiocyanatostibene-2,2'-disulfonic acid (DIDS) and diphenylamine 2-carboxylic acid (DPC), indicating that melatonin stimulated Cl - secretion. The effect of different melatonin analogs was compared and the order of potency appeased to be 2-iodomelatonin > melatonin > 6-hydroxymelatonin, indicating the involvement of melatonin receptors. However, inhibitors for G(i)-protein, adenylate cyclase or phospholipase C were found to be ineffective in inhibiting the melatonin-induced I(SC). Pretreatment of the cells with melatonin was also found to exert little effect on subsequent forskolin- or VIP-induced I(SC), further excluding its interaction with adenylate cyclase. Our data suggest that melatonin may play a role in regulating colonic Cl - secretion via melatonin receptors; however, the signal transduction pathway(s) involved remains to be elucidated.