Amino acid neurotransmitters in the CNS Relationships between net uptake and exchange in rat brain synaptosomes

AbstractCarefully isolated, metabolically competent rat brain synaptosomes accumulate acidic amino acid neuro-transmitters down to very low external levels. This supports the suggestion that nerve endings are involved in terminating transmission at the synapses and in maintaining low levels of these molecules in the external environment in the brain. At saturating levels of acidic amino acids, the rate of inward and outward movements of the Na+-amino acid complex (exchange) is much faster than the net uptake. The transmembrane gradients of aspartate and glutamate approach each other under all conditions explored which indicates that these two amino acids share the same transport system

The effect of thiol reagents on GABA transport in rat brain synaptosomes

AbstractThe nature of γ-aminobutyric acid (GABA) transport has been investigated in preparations of rat brain synaptosomes using a number of thiol reagents with varying membrane permeabilities. N-Ethylmaleimide, p-chloromercuribenzoate and p-chloromercuriphenylsulfonate effectively inhibited GABA transport in both directions (i.e., uptake and release) whereas 5,5′ -dithiobis-2-nitrobenzoate, mercaptopropionate and N-nitroethylenediamine were much less effective, or ineffective, even at millimolar concentrations. For each of the thiol reagents, the inhibition profile for GABA uptake was approximately the same as that for its release. The effectiveness of the reagents indicates that there is an external, reactable SH-group on the transporter, that the thiol reagent must be somewhat lipophilic for it to react with the SH-group(s) and that the same synaptosomal transport system is responsible for both uptake and release of GABA

The development of the respiratory chain of Saccharomyces carlsbergensis during respiratory adaptation

1. Subcellular fractionation of sphaeroplasts produced at different stages during the first 4h of respiratory adaptation of anaerobically grown glucose-de-repressed Saccharomyces carlsbergensis gave mitochondrial fractions that contained all the detectable c- and a-type cytochromes. 2. The rates of cytochrome formation were studied; individual cytochromes were produced at different rates so as to give respiratory chains having widely differing cytochrome ratios. A CO-reacting haemoprotein other than cytochrome a(3) also increased throughout 8h of respiratory adaptation. 3. Even after short periods of aeration, organisms contained mitochondria in which cytochrome–cytochrome interactions and the reaction of cytochrome a(3) with O(2) proceeded at rates almost as fast as in organelles from aerobically grown cells. 4. The technique of flow–flash photolysis enabled kinetic resolution of the reoxidation of cytochromes a(3) and a to be achieved and their individual contributions to extinction changes in the Soret region were assessed. The ratio cytochrome a(3)/cytochrome a increased over the early stages of adaptation