Activity assessment of organic cation/carnitine transporters in A549 alveolar epithelial cells

Abstract

Uptake and release of reported substrates via organic cation/carnitine transporters (OCT/Ns) was studied in A549 monolayers in an attempt to investigate the role of OCT/Ns in alveolar cell function. The OCT/N probes, ASP+, [14C]‐TEA and [3H]‐acetylcarnitine (Ac‐Car) were used in the experiments. [3H]‐verapamil, generally considered a substrate for P‐gp/MDR1, was also studied. The effect of time, temperature and various pharmacological agents on uptake and release of the compounds was investigated. All compounds exhibited temperature‐sensitive and time‐ and concentration‐dependent uptake and release. The involvement of both non saturable and saturable uptake carriers was observed in the case of the OCT/N probes. Km values were 27.8 μM (ASP+), 744.4 μM (TEA) and 17.7 μM (Ac‐Car), respectively. Uptake was significantly inhibited by MPP+, Decynium 22 and amantadine. Verapamil uptake was found to be saturable, mediated by a single transporter (Km 57.9 μM) and not inhibited by organic cations. The efflux of ASP+ from A549 monolayers was also saturable (Km 32.9 μM). L‐carnitine and amantadine had no significant effect on ASP+ efflux. Our data suggest that OCT/Ns are involved in membrane transport of organic cations in the alveolar epithelium. In addition, OCTs, but not OCTNs contributed to ASP+ efflux from A549 monolayers.