Single chloride channel currents from canine tracheal epithelial cells.

Patch-clamp techniques were used to characterize the properties of anion-selective channels in canine tracheal epithelial cells that had been maintained in primary culture. Gigaohm seals (10-30 G omega) were obtained in single isolated cells or cells at the edge of a confluent sheet, and channels were studied in the cell attached or the inside-out, excised patch configuration. Pretreatment with isotonic KCl caused the cells to round-up and allowed us to have better success in obtaining good seals. Based on conductance, anion-cation selectivity and voltage-dependent kinetic properties, four anion channel types could be detected in symmetrical solutions of 0.15 M NaCl: (i) a 30-50 pS Cl- channel of high selectivity, active at negative potentials and inactivated by large positive potentials; (ii) an approx. 20 pS Cl- channel of high selectivity, active at positive potentials and inactivated at negative potentials; (iii) an approx. 250 pS channel of moderate selectivity (PCl/PNa = 4) that was not voltage-dependent, and (iv) an approx. 10 pS Cl- channel with characteristics similar to (iii) above, but remaining somewhat active at large negative voltages. All excised patches were exposed to relatively high calcium concentrations on the intracellular side. Channel activity was increased in tracheal cells treated with 1 mM cAMP, suggesting that at least one of these channels plays a role in the increase of the apical membrane Cl- conductance that is mediated by cAMP and elicited by agonists of active Cl- secretion.