Characterization of a mouse colonic system B⁰⁺amino acid transporter related to amino acid absorption in colon

<jats:p>Previous experiments have shown that an amino acid transport system B<jats:sup>0+</jats:sup>transporter in cultured colonic epithelial cells mediates amino acid absorption. Here we describe the cloning and functional characterization of a system B<jats:sup>0+</jats:sup>transporter selectively expressed in the colon. Using the combination of an expressed sequence tag database search and RT-PCR approaches, we cloned a mouse colonic amino acid transporter, designated mCATB<jats:sup>0+</jats:sup>. Northern blot analysis revealed that mCATB<jats:sup>0+</jats:sup>was selectively expressed in the large intestine. In situ hybridization showed the mCATB<jats:sup>0+</jats:sup>mRNA to be localized in absorptive epithelial cells. When expressed in Xenopus oocytes, mCATB<jats:sup>0+</jats:sup>exhibited a Na<jats:sup>+</jats:sup>-dependent stereoselective uptake and a broad specificity for neutral and cationic amino acids, which is characteristic of amino acid transport system B<jats:sup>0+</jats:sup>. In vivo [<jats:sup>3</jats:sup>H]glycine uptake assay demonstrated that a system B<jats:sup>0+</jats:sup>-like transporter protein was expressed on the apical surface of the colonic absorptive cells. Our data suggest that a mouse colonic amino acid transporter mCATB<jats:sup>0+</jats:sup>may absorb amino acids from the intestinal contents in the colon.</jats:p>