Characterization of L-glutamine transport by type II alveolar cells.
This study characterized the sodium-dependent transport of L-glutamine (L-Gln) by rat type II alveolar cells. Uptake of 50 microM glutamine (Gln) was determined and found to be linear for at least 15 min. The sodium-dependent velocity represented greater than 80% of the total uptake at all time points. Kinetic studies of sodium-dependent Gln uptake at concentrations between 0.005 and 8 mM showed uptake to occur via two saturable transport systems, a high-affinity carrier [Michaelis constant (Km) = 259 +/- 19 microM, maximum velocity (Vmax) = 0.942 +/- 0.08 nmol.mg protein-1.30 s-1] and a low-affinity transporter (Km = 4.96 +/- 1.2 mM, Vmax = 2.98 +/- 0.19 nmol.mg protein-1.30 s-1). Uptake of Gln via the low-affinity system was nearly completely blocked by 10 mM 2-methylaminoisobutyric acid (MeAIB), and increasing concentrations of Gln almost totally inhibited transport of MeAIB, indicating the presence of system A. Further inhibition studies of the high-affinity transporter showed marked inhibition by serine, cysteine, and nonradioactive Gln. Lithium did not substitute for sodium, strongly suggesting that L-Gln was not transported by system N. Furthermore, transport of Gln by the high-affinity carrier was not affected by hormones or by changes in external pH. We conclude that sodium-dependent L-Gln transport by rat type II alveolar cells occurs predominantly via system A and system ASC.
Hautamaki
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RD
Department of Surgery, University of Florida College of Medicine, Gainesville 32610-0286.
Greene
B
B
Souba
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WW
D000596:Amino Acids / Q000494:pharmacology; D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002412:Cations / Q000494:pharmacology; D005973:Glutamine / Q000493:pharmacokinetics*; D006728:Hormones / Q000502:physiology; D006863:Hydrogen-Ion Concentration; D011650:Pulmonary Alveoli / Q000166:cytology / Q000378:metabolism*; D013997:Time Factors
D000596:Amino Acids; D002412:Cations; D006728:Hormones; D005973:Glutamine