L-trans-pyrrolidine-2,4-dicarboxylate and cis-1-aminocyclobutane-1,3-dicarboxylate behave as transportable, competitive inhibitors of the high-affinity glutamate transporters.
The ability of two conformationally restricted analogues of L-glutamate to function as non-transportable inhibitors of plasma membrane L-glutamate transport was investigated in primary cultures of cerebellar granule cells and cortical astrocytes. L-trans-Pyrrolidine-2,4-dicarboxylic acid (L-trans-PDC) and cis-1-aminocyclobutane-1,3-dicarboxylic acid (cis-ACBD) behaved as linear competitive inhibitors of the uptake of D-[3H]aspartate (used as a non-metabolizable analogue of L-glutamate) exhibiting Ki values between 40 and 145 microM; L-trans-PDC being the more potent inhibitor in each preparation. However, both L-trans-PDC and cis-ACBD, over a concentration range of 1 microM-5 mM, dose-dependently stimulated the release of exogenously supplied D-[3H]aspartate from granule cells maintained in a continuous superfusion system. The stimulated release was independent of extracellular calcium ions; essentially superimposable dose-response profiles being obtained in the absence and presence of 1.3 mM CaCl2 and yielding EC50 values of 16-25 microM and 180-220 microM for L-trans-PDC and cis-ACBD, respectively. Stimulated release of D-[3H]aspartate was unaffected by either 300 microM D-(-)-2-amino-5-phosphonopentanoic acid [D-APV; a selective antagonist of the N-methyl-D-aspartate (NMDA) receptor] or by 25 microM 6-cyano-7-nitroquinoxaline-2,3-dione [CNQX; a selective antagonist of the alpha-amino-3-hydroxy-5-methyl-4-isoxazole-propionic acid (AMPA) receptor]. The release of D-[3H]-aspartate following stimulation by either L-trans-PDC or cis-ACBD was however markedly attenuated following substitution in the superfusion medium of sodium ions by choline ions. Taken together, these results support an action of L-trans-PDC and cis-ACBD consistent with that of being competitive substrates rather than non-transportable blockers of the plasma membrane L-glutamate uptake system.
Griffiths
R
R
Division of Cell of Molecular Biology, School of Biological and Medical Sciences, University of St. Andrews, Fife, U.K.
Dunlop
J
J
Gorman
A
A
Senior
J
J
Grieve
A
A
D027322:Amino Acid Transport System X-AG; D000818:Animals; D001224:Aspartic Acid / Q000032:analysis; D001253:Astrocytes / Q000187:drug effects* / Q000378:metabolism; D002478:Cells, Cultured; D002794:Choline / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D018691:Excitatory Amino Acid Antagonists; D005971:Glutamates / Q000494:pharmacology; D018698:Glutamic Acid; D006023:Glycoproteins / Q000037:antagonists & inhibitors; D007700:Kinetics; D051379:Mice; D009474:Neurons / Q000187:drug effects* / Q000378:metabolism; D014179:Neurotransmitter Uptake Inhibitors / Q000494:pharmacology*; D012964:Sodium / Q000378:metabolism; D013237:Stereoisomerism
D027322:Amino Acid Transport System X-AG; D018691:Excitatory Amino Acid Antagonists; D005971:Glutamates; D006023:Glycoproteins; D014179:Neurotransmitter Uptake Inhibitors; C066302:2,4-methanoglutamate; D001224:Aspartic Acid; D018698:Glutamic Acid; D012964:Sodium; D002794:Choline