An electrogenic amino acid transporter in the apical membrane of cultured human bronchial epithelial cells.

We performed Ussing chamber experiments on cultured human bronchial epithelial cells to look for the presence of electrogenic dibasic amino acid transport. Apical but not basolaterall-arginine (10-1,000 μM) increased the short-circuit current. Maximal effect and EC50 were ∼3.5 μA/cm2 and 80 μM, respectively, in cells from normal subjects and cystic fibrosis patients. The involvement of nitric oxide was ruled out because a nitric oxide synthase inhibitor ( N G-nitro-l-arginine methyl ester) did not decrease the arginine-dependent current. Apicall-lysine,l-alanine, andl-proline, but not aspartic acid, were also effective in increasing the short-circuit current, with EC50 values ranging from 26 to 971 μM. Experiments performed with radiolabeled arginine demonstrated the presence of an Na+-dependent concentrative transporter on the apical membrane of bronchial cells. This transporter could be important in vivo to maintain a low amino acid concentration in the fluid covering the airway surface.