Single apical membrane anion channels in primary cultures of canine tracheal epithelium.

To investigate the cellular mechanism responsible for the apical membrane Cl conductance in airway epithelia, we used the patch-clamp technique to study single ion channels in primary cultures of canine tracheal epithelium. The cells contained an anion channel that had a single channel conductance of approximately 29 pS at negative voltages in symmetrical 145 mmol/l Cl solutions. In symmetrical Cl solutions the excised single-channel current-voltage relation was nonlinear, with conductance increasing at depolarizing voltages. The channel was inhibited by diphenylamine-2-carboxylate and anthracene-9-carboxylic acid at concentrations similar to those required to inhibit transepithelial Cl secretion. The channel was found in freshly isolated cells, isolated cells in culture, and in the apical membrane of confluent areas of cells. When attached to the cell the channel was activated by addition of isoproterenol in some, but not all cases. Often it was not observed to open until the patch was excised from the cell. The channel was not strongly voltage-gated, nor was it acutely regulated by internal Ca in the excised, inside-out configuration. These results suggest that this channel may be responsible for the apical Cl conductance in canine tracheal epithelium.