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

The regulated Cl- secretory apparatus of T84 cells responds to several phar macological agents via different second messengers (Ca2+, cAMP, cGMP). Howe ver, information about water movements in T84 cells has not been available. In the absence of osmotic or chemical gradient, we observed a net secretor y transepithelial volume flux (J(w), = -0.16 +/-0.02 mu1.min(-1).cm(-2)) in parallel with moderate short-circuit current values (I-sc = 1.55 +/-0.23 m uA/cm(2)). The secretory J(w) reversibly reverted to an absorptive value wh en A-23187 was added to the serosal bath. Vasoactive intestinal polypeptide increased I-sc, but, unexpectedly, J(w) was not affected. Bumetanide, an i nhibitor of basolateral Na+-K+-2Cl(-) cotransporter, completely blocked sec retory J(w) with no change in I-sc. Conversely, serosal forskolin increased I-sc, but J(w) switched from secretory to absorptive values. Escherichia c oli heat-stable enterotoxin increased secretory J(w) and I-sc. No differenc e between the absorptive and secretory unidirectional Cl- fluxes was observ ed in basal conditions, but after STa stimulation, a significant net secret ory Cl- flux developed. We conclude that, under these conditions, the prese nce of secretory or absorptive J(w) values cannot be shown by I-sc and ion flux studies. Furthermore, RT-PCR experiments indicate that aquaporins were not expressed in T84 cells. The molecular pathway for water secretion appe ars to be transcellular, moving through the lipid bilayer or, as recently p roposed, through water-solute cotransporters.