AN OUTWARDLY RECTIFYING CHLORIDE CHANNEL IN A HUMAN SUBMANDIBULAR-GLAND DUCT CELL-LINE (HSG)

We have used the single channel patch-clamp technique to study the ion channels in the plasma membrane of the HSG human submandibular gland duct cell line. When the pipette contained an isotonic KCl-rich soluti on and the bath an isotonic NaCl-rich solution, the predominant channe l type seen in excised inside-out patches was a Cl- channel with an ou twardly rectifying I-V relation that had a conductance of 12 pS at pos itive pipette potentials and 43 pS at negative pipette potentials. The channel was only seen in excised patches and its open probability was not significantly increased by membrane depolarization. The channel s electivity sequence (relative to Cl-) was estimated from reversal pote ntial measurements to be SCN- > NO3- > I- approximate to Cl- approxima te to Br- > acetate. In inside-out patches the channel was blocked by addition of 5-nitro-2-(3-phenylpropylamino)benzoate (NPPB) (100 mu mol /l) to the bath but not by 9-anthracene carboxylic acid (9-AC) (100 mu mol/l). The channel was not activated by increases in the free Ca2+ c oncentration on the cytosolic surface.