Transport of neutral, cationic and anionic amino acids by systems B, b(o,+), X(AG), and ASC in swine small intestine

• Published in: Comparative biochemistry and physiology. Part A, Molecular & integrative physiology Molecular & integrative physiology, 2000-08, Vol.126 (4), p.527-537
• Main Authors: Munck, L K, Grondahl, M L, Thorboll, J E, Skadhauge, E, Munck, B G
• Format: Article
• Language: English
• Subjects: Amino Acids - metabolism; Animals; Anions; Biological Transport; Cations; Female; Intestine, Small - metabolism; Kinetics; Microvilli - metabolism; Swine
• ISSN: 1095-6433
• DOI: 10.1016/S1095-6433(00)00227-0

Amino acid influx across the brush border membrane of the intact pig ileal epithelium was studied. It was examine whether in addition to system B, systems ASC and b(o,+) were involved in transport of bipolar amino acids. The kinetics of interactions between lysine and leucine demonstrates that system b(o,+) is present and accessible also to L-glutamine. D-aspartate (K(1/2) 0.3 mM) and L-glutamate (K(i) 0.5 mM) share a high affinity transporter with a maximum rate of 1.3 micromol cm(-2) h(-1), while only L-glutamate with a K(1/2) of 14.4 mM uses a low affinity transporter with a maximum rate of 2. 7 micromol cm(-2) h(-1), system ASC, against which serine has a K(i) of 1.6 mM. In the presence of 100 mM lysine, L-glutamine (A), leucine (B), and methionine (C) fulfilled the criteria of the ABC test for transport by one and the same transporter. However, serine inhibits not only transport of L-glutamate but also of glutamine (K(i) 0.5 mM), and L-glutamate inhibits part of the transport of glutamine. The test does, therefore, only indicate that the three bipolar amino acids have similar affinities for transport by systems B and ASC. Further study of the function of system B must be carried out under full inhibition by lysine and glutamate.