Voltage sensitive, high-conductance chloride channels in the luminal membrane of cultured pulmonary alveolar (type II) cells.

The properties of ion channels in patches from the luminal membrane of cultured monolayers of type II alveolar epithelial cells from adult rat lung have been studied. In excised patches, prepared as described to yield the "outside-out" configuration (with cesium ions in the bathing solutions to suppress currents arising from potassium channels), we observed anion-selective channels with a conductance of 350-400 pS, and burst lengths lasting seconds. When patches were bathed in solutions with equal chloride concentrations, channels opened and closed spontaneously at membrane voltages close to zero, but tended to close when the potential was shifted by +/- 10 mV, particularly in the negative direction. Other anions could pass through these channels with a permeability sequence of I(1.5) greater than Br(1.02) = greater than Cl(1.00) greater than NO3(0.9) greater than gluconate(0.6) but there was a very low permeability for sodium (PNa/PCl = 0.015 +/- 0.006). Calcium ions reduced channel conductance. The channels probably have a role to play in salt absorption by this epithelium, but insufficient information is available about how sodium crosses it for the role of the anion channels in transport to be defined with confidence.