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

Ugawa, Shinya, Yoko Sunouchi, Takashi Ueda, Eri Takahashi, Yoshitsugu Saishin, and Shoichi Shimada. Characterization of a mouse colonic system B01 amino acid transporter related to amino acid absorption in colon. Am J Physiol Gastrointest Liver Physiol 281: G365–G370, 2001.—Previous experiments have shown that an amino acid transport system B01 transporter in cultured colonic epithelial cells mediates amino acid absorption. Here we describe the cloning and functional characterization of a system B01 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 mCATB01. Northern blot analysis revealed that mCATB01 was selectively expressed in the large intestine. In situ hybridization showed the mCATB01 mRNA to be localized in absorptive epithelial cells. When expressed in Xenopus oocytes, mCATB01 exhibited a Na-dependent stereoselective uptake and a broad specificity for neutral and cationic amino acids, which is characteristic of amino acid transport system B01. In vivo [3H]glycine uptake assay demonstrated that a system B01-like transporter protein was expressed on the apical surface of the colonic absorptive cells. Our data suggest that a mouse colonic amino acid transporter mCATB01 may absorb amino acids from the intestinal contents in the colon.