CARBACHOL STIMULATES CL- SECRETION VIA ACTIVATION OF 2 DISTINCT APICAL CL- PATHWAYS IN CULTURED HUMAN T-84 INTESTINAL EPITHELIAL MONOLAYERS

The mode of action of carbachol in stimulation of transepithelial Cl- secretion in intact human intestinal T-84 epithelial monolayers has be en investigated in order to determine whether a DIDS-insensitive exit pathway (via CFTR) coexists with a DIDS-sensitive exit pathway at the apical membrane. Carbachol stimulates a transient inward I-sc due to C l- secretion whose magnitude is related to the basal level of inward I -sc. The inward current responses to both carbachol and hypo-osmotic m edia are abolished in nominally Ca2+-free media. The action of apical DIDS (100 mu M) upon carbachol-stimulated I-sc depends on the initial value of the basal I-sc. At basal I-sc levels < 10 mu A cm(-2), 100 mu M DIDS applied to the apical cell border abolishes the inward I-sc fo llowing exposure to both carbachol and hypo-osmotic media. In contrast a VIP-stimulated inward I,, is observed in the presence of 100 mu M D IDS. After VIP stimulation of inward I-sc, or if spontaneous basal val ues of I-sc were > 10 mu A cm(-2) the carbachol stimulation of inward I-sc was largely insensitive to 100 mu M DIDS. The data are consistent with the participation of both DIDS-sensitive and DIDS insensitive pa thways for Cl- at the apical membrane of human intestinal T-84 epithel ial cells.