Characteristics of Cl- uptake in rat alveolar type I cells.

Am J Physiol Lung Cell Mol Physiol. 2009 Aug 14; Johnson M, Allen L, Dobbs LGAlthough Cl(-) transport in fetal lung is important for fluid secretion and normal lung development, the role of Cl(-) transport in adult lung is not well understood. In physiologic studies, the cystic fibrosis transmembrane regulator CFTR plays a role in fluid absorption in the distal airspaces of adult lung and alveolar type II cells cultured for 5 days have the capacity to transport Cl(-). Although both alveolar type I and type II cells express CFTR, it has previously not been known whether type I cells transport Cl(-). We studied Cl(-) uptake in isolated type I cells directly, using either radioisotopic tracers or halide-sensitive fluorescent indicators. By both methods, type I cells take up Cl(-). In the presence of beta-adrenergic agonist stimulation, Cl(-) uptake can be inhibited by CFTR antagonists. Type I cells express both the Cl(-)/HCO3(-) anion exchanger AE2 and the voltage-gated chloride channels CLC5 and CLC2. Inhibitors of AE2 also block Cl(-) uptake in type I cells. Taken together, these results demonstrate that type I cells are capable of Cl(-) uptake and suggest that the effects seen in whole lung studies establishing the importance of Cl(-) movement in alveolar fluid clearance may be, in part, the result of Cl(-) transport across type I cells. Key words: chloride transport, alveolar type I cells, CFTR, CLC5.