Characterisation of volume-activated ion transport across epithelial monolayers of human intestinal T84 cells

The effects of hypo-osmolarity upon transepithelial ion transport in human intestinal cell layers have been investigated. Exposure of the basal-lateral surfaces to hypo-osmotic media resulted in a transient stimulation of inward short-circuit current (Isc). This transient stimulation of inward current by hypo-osmotic media was abolished by 100 mumol/l 4,4'-diisothiocyanostilbene-2,2'-disulphonic acid (DIDS). After prestimulation of inward Isc by vasoactive intestinal peptide (VIP) or by combinations of carbachol and prostaglandin E1, hypo-osmotic exposure of the basal-lateral surfaces resulted in a further transient stimulation of Isc. The stimulation of Isc in these conditions was largely insensitive to DIDS inhibition. Exposure of the basal-lateral surfaces to hypo-osmotic media resulted in a stimulation of loop-diuretic-insensitive 86Rb efflux across the basal-lateral surfaces. In addition, hypo-osmotic exposure of T84 cells is also associated with an increase in cytosolic Ca2+. It is concluded that the effects of hypo-osmotic exposure of T84 cells on secretory Isc are consistent with the activation of a DIDS-sensitive apical Cl- conductance and a basal-lateral K+ conductance. With prior activation of inward Isc by VIP via a cAMP-activated DIDS-insensitive apical Cl- conductance, augmentation of the secretory current by hypo-osmotic exposure is likely to result primarily from increased basal-lateral K+ current and loop-diuretic-sensitive Cl- uptake.