Amino acid neurotransmitters in the CNS. Characteristics of the acidic amino acid exchange.
D-Aspartate exchange, defined as amino acid-stimulated D-[3H]aspartate efflux, was investigated in a preparation of rat brain synaptosomes. The efflux of radiolabelled D-aspartate was found to be enhanced by micromolar concentrations of externally added D- and L-aspartate, L-glutamate, L-cysteate and L-cysteinesulphinate. The stimulation of release by external amino acids followed Michaelis-Menten kinetics; the apparent Km values (in microM) were: 14.65 +/- 0.98 for D-aspartate; 8.00 +/- 1.5 for L-aspartate; 22.31 +/- 1.62 for L-glutamate; 6.76 +/- 0.3 for L-cysteate and 7.89 +/- 1.23 for L-cysteinesulphinate. The Vmax values for efflux were 2.16-4.06 nmol/min per mg protein. The exchange process was found to require external NaCl but was very little affected by increase in the external [K+]. The demonstration of exchange as a part of the transport process provides support for the suggestion that in synaptosomal preparations a substantial portion of influx and efflux of amino acid neurotransmitters occurs via a reversible membrane carrier.
Erecińska
M
M
Troeger
M B
MB
D000596:Amino Acids / Q000494:pharmacology*; D000603:Amino Acids, Sulfur / Q000494:pharmacology*; D000818:Animals; D001224:Aspartic Acid / Q000378:metabolism* / Q000494:pharmacology; D001692:Biological Transport / Q000187:drug effects; D001923:Brain Chemistry; D003544:Cysteic Acid / Q000494:pharmacology*; D003545:Cysteine / Q000031:analogs & derivatives / Q000494:pharmacology; D005971:Glutamates / Q000494:pharmacology*; D018698:Glutamic Acid; D007700:Kinetics; D018377:Neurotransmitter Agents / Q000494:pharmacology*; D051381:Rats; D013268:Stimulation, Chemical; D013574:Synaptosomes / Q000378:metabolism
D000596:Amino Acids; D000603:Amino Acids, Sulfur; D005971:Glutamates; D018377:Neurotransmitter Agents; D001224:Aspartic Acid; D018698:Glutamic Acid; D003544:Cysteic Acid; D003545:Cysteine; C013461:cysteine sulfinic acid