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The transport of L-glutamic acid has been studied in skin-derived diploid human fibroblasts. Competition analysis in the presence and absence of Na+ and mathematical discrimination by nonlinear regression indicated that L-glutamic acid enters the cell by at least three transport systems: 1) a high affinity Na+-dependent system which has been found to be identical to the previously described system for anionic amino acids (Gazzola, G. C., Dall'Asta, V., Bussolati, O., Makowske, M., and Christensen, H. N. (1981) J. Biol. Chem. 256, 6054-6059) and which is provisionally designated as System X-AG; this route was shared by L-aspartic acid; 2) a low affinity Na+-dependent system resembling the ASC System for neutral amino acids (Franchi-Gazzola, R., Gazzola, G. C., Dall'Asta, V., and Guidotti, G. G. (1982) J. Biol. Chem. 257, 9582-9587); its reactivity toward L-glutamic acid was strongly inhibited by L-serine, but not by 2-(methyl-amino)isobutyric acid; and 3) a Na+-independent system similar to System XC- described in fetal human lung fibroblasts (Bannai, S., and Kitamura, E. (1980) J. Biol. Chem. 255, 2372-2376). The XC- system served for L-glutamic acid and L-cystine, the latter amino acid behaving as a potent inhibitor of L-glutamic acid uptake. Amino acid starvation did not change the uptake of L-glutamic acid by the two Na+-dependent systems, but enhanced the activity of System XC- by increasing its Vmax. L-Glutamic acid transport was also affected by the density of the culture. An increased cell density lowered the uptake of the amino acid by Systems ASC and XC- and promoted the uptake by System X-AG. All these variations were dependent upon changes in Vmax.
V Dall'Asta, and
G C Gazzola, and
R Franchi-Gazzola, and
O Bussolati, and
N Longo, and
G G Guidotti
January 1983,
Archives of neurology,
V Dall'Asta, and
G C Gazzola, and
R Franchi-Gazzola, and
O Bussolati, and
N Longo, and
G G Guidotti
May 1998,
Archives of biochemistry and biophysics,
V Dall'Asta, and
G C Gazzola, and
R Franchi-Gazzola, and
O Bussolati, and
N Longo, and
G G Guidotti
July 1988,
The American journal of physiology,
V Dall'Asta, and
G C Gazzola, and
R Franchi-Gazzola, and
O Bussolati, and
N Longo, and
G G Guidotti
April 1982,
The Journal of biological chemistry,
V Dall'Asta, and
G C Gazzola, and
R Franchi-Gazzola, and
O Bussolati, and
N Longo, and
G G Guidotti
October 1981,
Journal of cellular physiology,
V Dall'Asta, and
G C Gazzola, and
R Franchi-Gazzola, and
O Bussolati, and
N Longo, and
G G Guidotti
March 1984,
Experimental cell research,
V Dall'Asta, and
G C Gazzola, and
R Franchi-Gazzola, and
O Bussolati, and
N Longo, and
G G Guidotti
October 1969,
Lancet (London, England),
V Dall'Asta, and
G C Gazzola, and
R Franchi-Gazzola, and
O Bussolati, and
N Longo, and
G G Guidotti
October 1992,
The journal of histochemistry and cytochemistry : official journal of the Histochemistry Society,
V Dall'Asta, and
G C Gazzola, and
R Franchi-Gazzola, and
O Bussolati, and
N Longo, and
G G Guidotti
October 1987,
The Journal of clinical endocrinology and metabolism,
V Dall'Asta, and
G C Gazzola, and
R Franchi-Gazzola, and
O Bussolati, and
N Longo, and
G G Guidotti
October 1979,
The Journal of biological chemistry,
