CLONING AND FUNCTIONAL CHARACTERIZATION OF AMINO ACID TRANSPORTER B~(0,+) (ATB~(0,+)) IN PRIMARY CULTURED RAT PNEUMOCYTES

摘要

We cloned the rat ATB~(0,+) (rATB~(0,+)) in rat alveolar epithelial cells and investigated its functions. The rATB~(0,+) expressed in rat alveolar cells is about 3.2kb. The open reading frame encodes for a protein of 640 amino acids with 12 putative transmembrane domains. The transporter exhibited Na~+ and Cl~- coupled transport. All zwitterionic amino acids (except for proline) and cationic amino acids inhibited uptake of arginine. On the other hand, anionic amino acids, which are not substrates for ATB~(0,+), did not inhibit arginine uptake. Kinetic analyses indicated that the maximal velocity (V_(max)) and Michaelis-Menten constant (K_t) are 33.32 +-2.12 pmol/mg protein/15 min and 0.504 +- 0.114 mM, respectively. Our results indicate that rat pneumocytes express the amino acid transport system B~(0,+).