Electrogenic amino acid exchange via the rBAT transporter

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Abstract
A cDNA clone was isolated from rabbit renal cortex using DNA‐mediated expression cloning, which caused alanine‐dependent outward currents when expressed in Xenopus oocytes. The cDNA encodes rBAT, a Na‐independent amino acid transporter previously cloned elsewhere. Exposure of cDNA‐injected oocytes to neutral amino acids led to voltage‐dependent outward currents, but inward currents were seen upon exposure to basic amino acids. Assuming one charge/alanine, the outward current represented 38% of the rate of uptake of radiolabelled alanine, and was significantly reduced by prolonged preincubation of oocytes in 5 mM alanine. The currents were shown to be due to countertransport of basic amino acids for external amino acids using the cut‐open oocyte system. This transport represents a major mode of action of this protein, and may help in defining a physiological role for rBAT in the apical membrane of renal and intestinal cells.