Supported in part by the College of Agricultural and Life Sciences, University of Wisconsin-Madison, Madison, Wisconsin and by a grant, No. AM 10747, from the National Institutes of Health, U.S. Public Health Service, Bethesda, MD.
TRANSPORT OF THREONINE AND TRYPTOPHAN BY RAT BRAIN SLICES: RELATION TO OTHER AMINO ACIDS AT CONCENTRATIONS FOUND IN PLASMA1
Article first published online: 5 OCT 2006
Journal of Neurochemistry
Volume 31, Issue 3, pages 581–589, September 1978
How to Cite
Tews, J. K., Goodand, S. S. and Harper, A. E. (1978), TRANSPORT OF THREONINE AND TRYPTOPHAN BY RAT BRAIN SLICES: RELATION TO OTHER AMINO ACIDS AT CONCENTRATIONS FOUND IN PLASMA. Journal of Neurochemistry, 31: 581–589. doi: 10.1111/j.1471-4159.1978.tb07828.x
- Issue published online: 5 OCT 2006
- Article first published online: 5 OCT 2006
- Received 29 November 1977. Accepted 22 February 1978
Threonine content of brain decreases in young rats fed a threonine-limiting, low protein diet containing a supplement of small neutral amino acids (serine, glycine and alanine), which are competitors of threonine transport in other systems (Tewset al., 1977). Threonine transport by brain slices was inhibited more by a complex amino acid mixture resembling plasma from rats fed the small neutral amino acid supplement than by mixtures resembling plasma from control rats or from rats fed a supplement of large neutral amino acids. Greater inhibition was seen with mixtures containing only the small neutral amino acids than with mixtures containing only large neutral amino acids. On an equimolar basis, serine and alanine were the most inhibitory; large neutrals were moderately so; and glycine and lysine were without effect. Threonine transport was also strongly inhibited by α-amino-n-butyric acid and homoserine, less so by α-aminoisobutyric acid, and not at all by GABA.
The complex amino acid mixtures strongly inhibited α-aminoisobutyric acid transport by brain or liver slices but, in contrast to effects in brain, the extent of the inhibition in liver was not much affected by altering the composition of the mixture.
Tryptophan accumulation by brain slices was effectively inhibited by other large neutral amino acids in physiologically occurring concentrations. Threonine, or a mixture of serine, glycine and alanine only slightly inhibited tryptophan uptake; basic amino acids were without effect and histidine stimulated tryptophan transport slightly.
These results support the conclusion that a diet-induced decrease in the concentration in brain of a specific amino acid may be related to increased inhibition of its transport into brain by increases in the concentrations of transport-related, plasma amino acids.