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Am J Physiol Cell Physiol (January 9, 2002). doi:10.1152/ajpcell.00324.2001
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Articles in PresS, published online ahead of print January 9, 2002
Am J Physiol Cell Physiol, 10.1152/ajpcell.00324.2001
Submitted on July 17, 2001
Accepted on January 2, 2002

Characterization of L-glutamine transport by a human neuroblastoma cell line

Masafumi Wasa1*, Hong-Sheng Wang1, and Akira Okada1

1 Pediatric Surgery, Osaka University Graduate School of Medicine, Suita, Osaka, Japan

* To whom correspondence should be addressed. E-mail: wasa{at}pedsurg.med.osaka-u.ac.jp.

This study characterized the sodium-dependent transport of L-glutamine by a human neuroblastoma cell line, SK-N-SH. The sodium-dependent component represented more than 95% of the total glutamine uptake. Kinetic studies showed a single saturable high-affinity carrier with a Michaelis constant (Km) of 163 +/- 23 µM and a maximum transport velocity (Vmax) of 13,713 +/- 803 pmol/mg protein/min. Glutamine uptake was markedly inhibited in the presence of L-alanine, L-asparagine, and L-serine. Lithium did not substitute for sodium. These data show that L-glutamine is predominantly taken up through System ASC. Glutamine deprivation resulted in the decrease of glutamine transport by a mechanism that decreased Vmax without affecting Km. The expression of a System ASC subtype (ASCT2) decreased in the glutamine-deprived group, whereas glutamine deprivation did not induce changes in ASCT1 mRNA expression. An adaptive increase in sodium-dependent glutamate, sodium-dependent Me-AIB, and sodium-independent leucine transport was observed under glutamine-deprived conditions. These were completely blocked by actinomycin D and cycloheximide. These mechanisms may allow cells to survive and even grow under nutrient-deprived conditions.






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