Spontaneous water secretion in T84 cells: Effects of STa enterotoxin, bumetanide, VIP, forskolin, and A-23187

Abstract

The regulated Cl- secretory apparatus of T84 cells responds to several pharmacological agents via different second messengers (Ca2+, cAMP, cGMP). However, information about water movements in T84 cells has not been available. In the absence of osmotic or chemical gradient, we observed a net secretary transepithelial volume flux (Jw = -0.16 ± 0.02 μ1·min-1·cm-2) in parallel with moderate short-circuit current values (Isc = 1.55 ± 0.23 μA/cm2). The secretory Jw reversibly reverted to an absorptive value when A-23187 was added to the serosal bath. Vasoactive intestinal polypeptide increased Isc, but, unexpectedly, Jw was not affected. Bumetanide, an inhibitor of basolateral Na+-K+-2Cl- cotransporter, completely blocked secretory Jw with no change in Isc Conversely, serosal forskolin increased Isc, but Jw switched from secretory to absorptive values. Escherichia coli heatstable enterotoxin increased secretary Jw and Isc. No difference between the absorptive and secretory unidirectional Cl- fluxes was observed in basal conditions, but after STa stimulation, a significant net secretory Cl- flux developed. We conclude that, under these conditions, the presence of secretory or absorptive Jw values cannot be shown by Isc and ion flux studies. Furthermore, RT-PCR experiments indicate that aquaporins were not expressed in T84 cells. The molecular pathway for water secretion appears to be transcellular, moving through the lipid bilayer or, as recently proposed, through water-solute cotransporters.