Characterization of L-glutamine transport by pulmonary artery endothelial cells

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Abstract
This study characterized the transport of L-glutamine by porcine pulmonary artery endothelial cells (PAECs). Uptake of 50 microM glutamine was determined and found to be linear for at least 45 min. The sodium-dependent velocity represented greater than 95% of the total uptake at all time points. Kinetic studies of glutamine uptake at concentrations between 0.005 and 10 mM showed a single saturable high-affinity carrier with a Michaelis constant of 100 +/- 6 microM and a maximal transport velocity of 1.0 +/- 0.08 nmol.mg protein-1.30s-1. Glutamine uptake by PAECs was markedly inhibited in the presence of L-cysteine, L-threonine, or L-alanine; lesser degrees of inhibition occurred when histidine and arginine were added. 2-Methylaminoisobutyric acid and 2-aminobicyclo [2,2,1]heptanedicarboxylic acid had little effect on glutamine uptake. Lithium did not substitute for sodium, strongly suggesting that L-glutamine was not transported by system N. Furthermore, transport of glutamine was not affected by hormones or by changes in external pH. Based on the intolerance of this high-affinity carrier to N-methylated substrate, its insensitivity to pH and hormonal regulation, and the failure of lithium to substitute for sodium, as well as its inhibition by alanine and cysteine, we conclude that in porcine pulmonary artery endothelial cells L-glutamine is predominantly taken up through system ASC.

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