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Expression of amino acid transport systems in cultured human umbilical vein endothelial cells.

1989; Wiley; Volume: 410; Issue: 1 Linguagem: Inglês

10.1113/jphysiol.1989.sp017535

1469-7793

Giovanni E. Mann, Jeremy D. Pearson, C. J. Sheriff, VALERIE J. TOOTHILL,

Peroxisome Proliferator-Activated Receptors

1. Nutrient transport in cultured human umbilical vein endothelial cells was characterized using a rapid dual‐isotope dilution technique. Microcarrier beads with confluent endothelial cells were perfused in small columns, and uptake and efflux were assessed relative to D‐mannitol (extracellular tracer) during a single transit through the column. 2. At tracer concentrations significant unidirectional uptakes were measured for L‐leucine (53 +/‐ 2%), L‐phenylalanine (73 +/‐ 2%), L‐serine (40 +/‐ 4%), L‐arginine (42 +/‐ 3%) and L‐ornithine (26 +/‐ 3%). Uptake for L‐proline, D‐glucose, dopamine and serotonin was lower (6‐10%), whereas uptake for the system A analogue 2‐methylaminoisobutyric acid (2‐MeAIB) was negligible. Uptakes rapidly decreased with time due to tracer efflux. 3. Endothelial cell transport of L‐leucine was markedly inhibited during perfusion with 1 mM‐BCH (beta‐2‐aminobicyclo‐(2,2,1)‐heptane‐2‐carboxylic acid, system L analogue), L‐leucine, D‐leucine, L‐phenylalanine, L‐methionine and L‐DOPA. 2‐MeAIB, L‐cysteine, glycine, L‐proline, hydroxy‐L‐proline, L‐aspartate and beta‐alanine were poor inhibitors, while L‐serine and the cationic substrates L‐lysine and L‐arginine inhibited uptake by 10‐35%. 4. When the kinetics of L‐leucine transport were examined over a wide range of substrate concentrations (0.025‐1 mM) transport was saturable. A single entry site analysis gave a half‐maximal saturation constant Kt = 0.24 +/‐ 0.08 mM (mean +/‐ S.E.M., n = 5) and a Vmax = 27.8 +/‐ 4.6 nmol/min per column (approximately 3 x 10(6) cells). 5. Removal of sodium from the perfusate inhibited tracer uptake of L‐leucine, L‐serine and L‐arginine by respectively 20 +/‐ 5% (n = 3), 77 +/‐ 5% (n = 3) and 35 +/‐ 4% (n = 3). 6. Our results provide the first evidence that cultured human endothelial cells of venous origin express a saturable transport system for large neutral amino acids resembling system L described in brain microvascular endothelium. Detection of Na+‐dependent and Na+‐independent L‐arginine uptake is of interest in view of recent reports that this cationic amino acid may be the physiological precursor for nitric oxide released by endothelium.