SUMMARY1. During osmotic swelling, cultured human small intestinal epithelial cells (Intestine 407) exhibited activation of large Cl-currents under the patch-clamp whole-cell configuration. The volume-sensitive Cl-conductance was independent of intracellular Ca2+ and cyclic AMP.2. The anion permeability sequence of the current was SCN-> I-> Br-> Cl-> F-> gluconate-, corresponding to Eisenman's sequence I. 3. Cl-currents were instantaneously activated by command pulses in a range of -120 to + 45 mV. At potentials more positive than + 50 mV the current showed a time-dependent inactivation. This inactivation was accelerated by increased depolarization. The instantaneous current-voltage relationship rectified in the outward direction.4. A stilbene-derivative Cl-channel blocker, 4-acetamido-4'-isothiocyanostilbene (SITS), inhibited the Cl-current at micromolar concentrations. SITS facilitated inactivation at positive potentials. Outward currents were more prominently suppressed by SITS than inward currents. The concentrations required for 50% inhibition (IC50) of outward and inward currents were 1-5 and 6 EM, respectively. The outward and inward currents were equally inhibited by a carboxylate analogue Clchannel blocker, 5-nitro-2-(3-phenylpropylamino)-benzoate (NPPB)

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During osmotic swelling of a human intestinal epithelial cell line, stepwise closing unitary events of Cl- channels could be observed in cell-attached patches upon application of large positive potentials only when inactivating whole-cell Cl- currents were simultaneously observed. The closing process became faster with increasing positive command pulses. The unitary conductance was around 32 pS at 60 mV, 37 pS at +100 mV, and 47 pS at +140 mV exhibiting outward rectification.

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