Characteristics of acidic, basic and neutral amino acid transport in the perfused rat hindlimb.

作者：Harinder S. Hundal, Michael J. Rennie, Peter Watt · 发表于：The Journal of Physiology · 年份：1989 · DOI：10.1113/jphysiol.1989.sp017449 · 被引用次数：83 · 研究领域：Ion channel regulation and function、Amino Acid Enzymes and Metabolism、Neuroscience and Neuropharmacology Research

1. We have employed a paired-tracer isotope dilution technique in a perfused rat hindlimb preparation to obtain information on the kinetics of transport across the sarcolemmal membranes of acidic, neutral and basic amino acids. 2. We have defined the characteristics of the saturable transport of amino acids normally regarded as paradigm substrates for the A, ASC, L, y+(basic) and the dicarboxylic amino acid transport systems. Their maximal transport capacities (Vmax, nmol min-1 (g muscle)-1 and substrate concentrations for half-maximal transport (Km, mM) of representative amino acid substrates are as follows: 2-aminoisobutyrate (AIB), Vmax = 15 +/- 7, Km = 1.26 +/- 0.6; alanine, Vmax = 332 +/- 53, Km = 3.9 +/- 0.9; serine, Vmax = 410 +/- 61, Km 3.4 +/- 0.5; leucine, Vmax = 2800 +/- 420, Km = 20 +/- 2; lysine, Vmax = 136 +/- 46, Km = 2.1 +/- 1.3; glutamate, Vmax = 86 +/- 6, Km = 1.05 +/- 0.05; proline, Vmax = 196 +/- 48, Km = 4.1 +/- 0.6. 3. Glycine uptake was faster than expected on the basis of diffusion but was not saturable and showed uptake that could be best described by a first-order rate constant of 0.07 +/- 0.003 min-1. 4. We have attempted to discriminate kinetically between possible routes of entry for an amino acid on the basis of competitive and non-competitive interaction between substrates potentially sharing common routes. On this basis, the major routes of alanine entry appear to be via the ASC and L systems with the A system playing a quantitatively minor rol...