ALUNG April 22/4

Lazrak, A., A. Samanta, and S. Matalon. Biophysical properties and molecular characterization of amiloridesensitive sodium channels in A549 cells. Am J Physiol Lung Cell Mol Physiol 278: L848–L857, 2000.—Amiloride-sensitive Na1 channels, present in fetal and adult alveolar epithelial type II (ATII) cells, play a critical role in the reabsorption of fetal fluid shortly after birth and in limiting the extent of alveolar edema across the adult lung. Because of the difficulty in isolating and culturing ATII cells, there is considerable interest in characterizing the properties of ion channels and their response to injury of ATII cell-like cell lines such as A549 that derive from a human alveolar cell carcinoma. A549 cells were shown to contain a-, b-, and g-epithelial Na1 channel mRNAs. In the whole cell mode of the patch-clamp technique (bath, 145 mM Na1; pipette, 145 mM K1), A549 cells exhibited inward Na1 currents reversibly inhibited by amiloride, with an inhibition constant of 0.83 μM. Ion substitution studies showed that these channels were moderately selective for Na1 (Na1-to-K1 permeability ratio 5 6:1). Inward Na1 currents were activated by forskolin (10 μM) and inhibited by nitric oxide (300 nM) and cGMP. Recordings in cell-attached mode revealed the presence of an amiloridesensitive Na1 channel with a unitary conductance of 8.6 6 0.04 (SE) pS. Channel activity was increased by forskolin and decreased by nitric oxide and the cGMP analog 8-bromocGMP. These data demonstrate that A549 cells contain amiloride-sensitive Na1 channels with biophysical properties similar to those of ATII cells.