SEARCH

SEARCH BY CITATION

Keywords:

  • transport kinetics;
  • synaptosomal fractions;
  • uptake;
  • HPLC analysis

Abstract

The transport kinetics of the excitatory sulphur-containing amino acid (SAA) transmitter candidates, L-cysteine sulphinate (L-CSA), L-cysteate (L-CA), L-homocysteine sulphinate (L-HCSA), and L-homocysteate (L-HCA), together with their plasma membrane carrier specificity, was studied in cerebrocortical synaptosome fractions by a sensitive high performance liquid chromatographic assay. A high affinity uptake system could be demonstrated for L-CSA (Km =; 57 ± 6 μM; Vmax =; 1.2 ± 0.1 nmol/min/mg protein) and L-CA (Km =; 23 ± 3 μM; Vmax =; 3.6 ± 0.1 nmol/min/mg protein), whereas L-HCSA (Km =; 502 ± 152 μM; Vmax =; 6.1 ± 1.3 nmol/min/mg protein) and L-HCA (Km =; 1550 ± 169 μM; Vmax =; 10.3 ± 1.1 nmol/min/mg protein) exhibited much lower affinity as transport substrates. In all cases, only a single, saturable Na+-dependent component of uptake could be identified, co-existing with a non-saturable, Na+-independent influx component. Plasma membrane carrier specificity of the SAAs was established following comparison with other high-affinity neurotransmitter systems. High-affinity L-CSA and L-CA transport and low-affinity L-HCSA and L-HCA transport demonstrate strong positive correlations in inhibition profiles when compared against each other or individually against the high-affinity transport of L-[3H]glutamate, L-[3H]aspartate, or D-[3H]aspartate. Moreover, the transport systems for the excitatory SAAs exhibited a negative correlation when compared in inhibition profiles with the high affinity transport of both [3H] γ-aminobutyric acid (GABA) and [3H]taurine. Taken together, these results strongly suggest that L-CSA, L-CA, L-HCSA, and L-HCA share a common synaptosomal plasma membrane transport system with L-glutamate, L-aspartate, and D-aspartate. © 1992 Wiley-Liss, Inc.