Uptake of L-alanine, glycine and L-serine in the pigeon central nervous system.

The uptake characteristics of L-alpha-alanine, glycine and L-serine into crude mitochondrial fractions from pigeon telencephalon, tectum and spinal cord were determined. Sodium dependent high affinity uptake systems were found for all 3 amino acids in all 3 brain regions, except for glycine in the telencephalon. The mutual inhibition of the high affinity uptake by the 3 amino acids was measured in the tectum. Alanine uptake was inhibited competitively by serine and glycine. The inhibition of serine uptake by alanine and glycine was also competitive. In contrast, glycine uptake inhibition by alanine and serine was incomplete and neither competitive, non-competitive nor uncompetitive. The effect of various chemicals on the uptake of the 3 amino acids was measured in the tectum at a substrate concentration of 10(-5) M. Four groups could be distinguished: (1) Substances with no effect on the uptake of all 3 amino acids, (2) substances which inhibited the uptake of all 3 amino acids to a similar degree, (3) substances which inhibited the uptake of alanine and serine more than glycine and (4) substances which inhibited glycine uptake more than alanine and serine uptake. From these results we conclude: Alanine and serine are probably taken up by the same transport system. This system can possibly also use glycine as substrate. Most of the glycine high affinity uptake, however, is due to a specific glycine transport system. This system was found only in tectum and spinal cord and is probably the same uptake system as known in the spinal cord of other vertebrates.