Abstract
The basolateral amino acid transporters LAT2- and y+LAT1-4F2hc function as obligatory exchangers whereas the aromatic amino acid transporter TAT1 is known to function as a low affinity facilitated diffusion pathway. Using X. laevis oocytes we have shown that TAT1 can complement the transport function of LAT2-4F2hc by recycling exchange substrates and thus contribute to net amino acid (re)absorption. Under normal conditions, Tat1 knockout mice (Ingenium Pharmaceuticals) grow normally and show no gross phenotype: they exhibit increased plasma levels of Tyr and Trp, but no major aminoaciduria. However, when subjected to high protein diet, their urine contains several amino acids, whereas their plasma concentration remains stable. This data show that the lack of Tat1 impacts on the kinetics of net transepithelial (re)absorption of amino acids and their homeostasis. The lack of aminoaciduria observed under normal diet implies that at least one additional amino acid transporter capable of recycling exchange substrates is expressed in the same basolateral epithelial membranes. Nevertheless, as shown under high protein diet, this additional transporter(s) does not entirely compensate the absence of Tat1. Supported by Swiss NSF grant 31-130471 to François Verrey
Published Version
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