Osmosensitivity of the hyperpolarization-activated chloride current in human intestinal T84 cells

The osmosensitivity of the hyperpolarization-activated chloride current (I-Clhyp) in T84 cells was studied using the whole cell patch-clamp recording configuration. Hypotonicity is known to activate an outwardly rectify ing chloride current (HIORC) distinct from I-Clhyp in these cells. The differing sensitivities of HIORC and I-Clhyp, toward inhibitors (1,9-dideoxyforskolin blocked HIORC but not I-Clhyp, and Cd2+ inhibited I-Clhyp but not HIORC) allowed us to investigate the osmoregulation of I-Clhyp. Hypotonicity induced an increase in I-Clhyp amplitude. Protein phosphatase inhibitors prevented this effect, and hypotonic solutions became slightly inhibitory. Hypertonicity resulted in a transient increase in I-Clhyp amplitude followed by a large decrease. The complex responses of I-Clhyp to osmotic changes indicate that these signals affect the same channel via multiple transduction pathways. The responses of I-Clhyp to hypotonicity have features in common with the responses of ClC-2 channels expressed in Xenopus oocytes (activation) and with hyperpolarization-activated chloride currents in other cell types, such as osteoblasts and mandibular duct cells (inhibition).