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

We have used the single-channel patch-clamp technique tb study ion cha nnels in the plasma membrane of the HSG human submandibular gland duct cell line. In cell-attached and excised inside-out patches, at least six channel types were observed. When the pipette contained an isotoni c KCl-rich solution and the bath an isotonic NaCl-rich solution, the p redominant channel type seen in excised inside-out patches was a Cl- c hannel with an outwardly rectifying current/voltage (I/V) relation tha t had a conductance of 12 pS at positive pipette potentials and 43 pS at negative pipette potentials. The channel was only seen in excised p atches and its open probability was not significantly increased by mem brane depolarization. The channel selectivity sequence (relative to Cl -) was estimated from reversal potential measurements to be: SCN- (1.8 ) > NO3- (1.4) > I- (1.1) similar to Cl- (1) similar to Br- (0.8) > ac etate (0.35). In inside-out patches the channel was blocked by additio n 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+ concent ration on the cytosolic surface. This is the first report of an outwar dly rectifying Cl- channel in a salivary epithelium. The properties of this channel are not in accordance with the properties of the Cl- con ductances in the acinar or duct tissues which have been studied so far and its physiological role is unclear.