Endogenous arachidonic acid inhibits hypotonically-activated Cl- channels in isolated rat hepatocytes

Properties of hypotonically-activated Cl- channels in isolated rat hepatocytes were studied by the patch-clamp whole-cell technique. Hypotonic stress (140-150 mosmol kg 1 H2O) induced a hyperpolarization of the membrane of hepatocytes in the presence of an inwardly oriented Cl gradient, but had no effect on the membrane potential in the absence of Cl. An increase in the hypotonically-induced conductance was significantly inhibited by 4-acetamido-4'-isothiocyanatostilbene-2, 2'-disulfonic acid (SITS; 50 microM), but not by Ba2+ (1 mM). Pre-incubation with arachidonic acid (20 microM) significantly inhibited the hypotonically-activated conductance. The combined application of a cyclo-oxygenase inhibitor, indomethacin (50 microM) and a lipoxygenase inhibitor, esculetin (100 microM) also inhibited the conductance, whereas quinacrine (200 microM), a phospholipase A2 inhibitor, significantly induced a large steady conductance. Outward Cl- currents, but not cationic currents, were elicited by the hypotonic stress. The current did not show any rapid time-dependent inactivation during the voltage clamp of 0.1 s. The combined application of arachidonic acid, indomethacin and esculetin inhibited the hypotonically-activated Cl- currents. The present study has shown that the Cl- channel is activated by exposure to hypotonic stress and closed by an increase in arachidonic acid concentration in isolated rat hepatocytes.