Amino acid neurotransmitters in the CNS: effect of thiopental

Thiopental, a thiobarbiturate which partitions prefentially into the hydrophobic environment, inhibited transport of amino acid neurotransmitters, GABA, aspartate and glutamate, and of biogenic amine, dopamine, across the synaptosomal membrane. At a given protein and thiopental concentration GABA transport was more sensitive to the barbiturate than were the movements of aspartate and glutamate although the uptake of each amino acid was inhibited essentially to the same extent as was its K+-stimulated release. By contrast, inhibition of dopamine uptake was larger than that of its release. Thiopental also inhibited the release of amino acid neurotransmitters caused by anaerobiosis. It is suggested that the barbiturate modifies the properties of the synaptosomal lipids and/or hydrophobic segments of proteins and thereby, simultaneously and independently, affects various membrane functions. The equal inhibition of uptake and release of amino acid neurotransmitters is consistent with the postulate that their transport occurs through the reversible membrane carriers which function efficiently in both the inward and outward directions.