Effect of L-homocysteine and derivatives on the high-affinity uptake of taurine and GABA into synaptosomes and cultured neurons and astrocytes.

The effect of L-homocysteine and selected derivatives on the high-affinity uptake of the inhibitory neuroeffectors, GABA and taurine, was investigated in synaptosomes, and in cultured neurons and astrocytes. High-affinity uptake of taurine into synaptosomes was inhibited most effectively by L-homocysteine, DL-homocysteine and homocystine whereas neuronal uptake was unaffected by any of the compounds tested. The high affinity uptake of taurine into astrocytes was markedly inhibited by L-homocysteine, L-homocysteic acid and L-homocystine. High-affinity GABA uptake into astrocytes was notably inhibited by L-homocystine, none of the other compounds tested causing appreciable inhibition below a concentration of 5 mM. Neuronal and synaptosomal high-affinity uptake of GABA was not significantly affected by any of the test compounds at concentrations below 5 mM. The implication of these results to the study of the mechanism of homocysteine-induced seizures and their relevance to the genetic disorder homocystinuria is discussed.