A CA2+-ACTIVATED 23-PS K+ CHANNEL IN A HUMAN SUBMANDIBULAR-GLAND DUCT CELL-LINE (HSG)

We have used single-channel patch-clamp techniques to study K+ channels in the HSG cell line derived from the ducts of the human submandibular gland. In contrast to the secretory cells of the acini (or endpieces), duct cells are believed to absorb rather than to secrete NaCl and water, although both cell types secrete K+ ions. Consequently, we expected to find a rather different pattern of channel activity in HSG cells to that previously reported in numerous studies on secretory endpiece cells. In excised, inside-out patches we observed a K+ channel that had a linear current-voltage relation with a conductance of 23 pS in symmetrical K+ conditions. The channel selectivity sequence as estimated by reversal potential measurements was (relative to K+): K+ (1) > Rb+ (0.61) > Cs+ (0.43) > Na+ (< 0.15). In outside-out patches, the channel was blocked by the addition to the bathing solution of quinine (1 mmol/l) or the venom of the scorpion, Leiurus quinquestratus hebraeus (138 mu g/ml). Channel activity in inside-out patches was increased by increasing cytosolic free Ca2+ concentration. In cell-attached patches the channel was activated by addition of the muscarinic agonist, carbachol (10-100 mu mol/l), to the bath solution. Since these features are very similar to those of the Rb+ efflux pathway previously reported in this cell line, we conclude that the 23-pS K+ channel may provide the means by which muscarinic stimulation regulates K+ transport by HSG cells. If the ion channel population in the HSG cell line is similar to the population in intralobular duct cells, then these studies provide a possible mechanism for the stimulation of ductal K+ secretion by muscarinic agonists.