Inhibition of the high-affinity uptake of D-[3H]aspartate in rate by L-alpha-aminoadipate and arachidonic acid.
The mechanism of inhibition of the high-affinity sodium-dependent transport of D-[3H]aspartate by the gliotoxin, L-alpha-aminoadipate, and also by the endogenous fatty acid, arachidonic acid (cis-5,8,11,14 eicosatetraenoic acid), into rat brain synaptosomes has been investigated. L-alpha-Aminoadipate competitively inhibited the transport of D-[3H]aspartate with a K1 value of 192 microM. Superfusion of coronal slices of rat brain for 40 min with 1 mM L-alpha-aminoadipate reduced the glutathione concentration of the tissue by 20%. Neither glutamate nor kainate depleted the glutathione level of the slices. Pre-incubation of synaptosomes with arachidonic acid (10 microM) for 10-60 min produced a marked potentiation of the inhibition of D-[3H]aspartate transport, compared to experiments in which the acid was added concurrently with the D-[3H]aspartate ('co-incubation' experiments). Inhibition of D-[3H]aspartate transport by arachidonic acid was not blocked by addition of nordihydroguaretic acid to the pre-incubation medium. Staurosporine (50 nM) reduced the inhibition of transport occurring during pre-incubation with 10 microM arachidonic acid, and there was no longer any significant difference from the level of inhibition obtained in co-incubation experiments. Phorbol, 12-myristate, 13-acetate (1 microM) reduced the transport of D-[3H]aspartate to 73% of control after 20 min pre-incubation of the synaptosomes. This study highlights the fact that inhibition of glutamate transport may affect brain function in a number of different ways. Competitive inhibition by a structural analogue of glutamate, such as L-alpha-aminoadipate, leads to a reduction in the glutathione level, which may be an important factor in L-alpha-aminoadipate-mediated toxicity. On the other hand, the more long-term effects of non-competitive inhibition of glutamate transport by arachidonic acid, in a mechanism involving protein kinase C, may represent a physiological means for regulation of transporter activity in the brain.
Lundy
D F
DF
Department of Biochemistry, University College, Berfield, Dublin, Ireland.
McBean
G J
GJ
D015074:2-Aminoadipic Acid / Q000494:pharmacology*; D000818:Animals; D016718:Arachidonic Acid / Q000494:pharmacology*; D001224:Aspartic Acid / Q000493:pharmacokinetics*; D001692:Biological Transport / Q000187:drug effects; D001921:Brain / Q000187:drug effects / Q000201:enzymology; D001923:Brain Chemistry / Q000502:physiology*; D002273:Carcinogens / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005974:Glutamate-Ammonia Ligase / Q000037:antagonists & inhibitors; D005721:Glutamate-Cysteine Ligase / Q000037:antagonists & inhibitors; D018698:Glutamic Acid / Q000378:metabolism; D009924:Organ Culture Techniques; D010703:Phorbol Esters / Q000494:pharmacology; D051381:Rats; D019311:Staurosporine / Q000494:pharmacology; D014316:Tritium
D002273:Carcinogens; D004791:Enzyme Inhibitors; D010703:Phorbol Esters; D014316:Tritium; D015074:2-Aminoadipic Acid; D016718:Arachidonic Acid; D001224:Aspartic Acid; D018698:Glutamic Acid; D005974:Glutamate-Ammonia Ligase; D005721:Glutamate-Cysteine Ligase; D019311:Staurosporine