Effects of acromelic acid A on the binding of [3H]-kainic acid and [3H]-AMPA to rat brain synaptic plasma membranes.
1. The ability of acromelic acid A to inhibit [3H]-kainic acid and [3H]-(RS)-alpha-amino-3-hydroxy-5-methyloxazole-4-propionic acid ([3H]-AMPA) binding to rat brain synaptic plasma membranes was investigated by equilibrium radioligand binding assay. 2. Kinetic analysis of [3H]-kainic acid binding demonstrated the existence of two kainate binding sites in this tissue preparation and yielded equilibrium dissociation constants for [3H]-kainic acid of KD = 0.4 nM and KD = 20.8 nM. 3. Kainic acid and domoic acid both appeared to displace [3H]-kainic acid from a single binding site with equilibrium binding constants of KD = 19.4 nM and Ki = 14.5 nM respectively. Acromelic acid A exhibited a biphasic inhibition of [3H]-kainic acid binding to synaptic membranes with binding affinities of Ki = 15.1 nM and Ki = 1.49 microM. 4. In the absence of chaotropic ions, the order of potency of inhibition of [3H]-AMPA binding was acromelic acid A (Ki = 26 nM) greater than AMPA (KD = 184 nM) greater than domoic acid (Ki = 499 nM). 5. The inclusion of 100 mM thiocynanate ion in the [3H]-AMPA binding assay resulted in a change in the order of potency to: AMPA (KD = 160 nM) greater than acromelic acid A (Ki = 289 nM) greater than domoic acid (Ki = 9.02 microM). 6. These results show that acromelic acid A distinguishes two kainate binding sites in rat brain synaptic plasma membranes and in addition, that in the absence of chaotropic ions, acromelic acid A is the most potent displacer of [3H]-AMPA binding yet described.
Smith
A L
AL
MRC Anatomical Neuropharmacology Unit, Oxford.
McIlhinney
R A
RA
D000818:Animals; D001921:Brain / Q000187:drug effects* / Q000378:metabolism; D005260:Female; D007051:Ibotenic Acid / Q000031:analogs & derivatives* / Q000378:metabolism; D007608:Kainic Acid / Q000031:analogs & derivatives* / Q000378:metabolism* / Q000494:pharmacology; D007700:Kinetics; D011804:Quinolines / Q000494:pharmacology*; D011869:Radioligand Assay; D051381:Rats; D011919:Rats, Inbred Strains; D013570:Synaptic Membranes / Q000187:drug effects* / Q000378:metabolism; D018350:alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid
D011804:Quinolines; C049740:alpha-pentyl-3-(2-quinolinylmethoxy)benzenemethanol; D007051:Ibotenic Acid; D018350:alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid; C051743:acromelic acid A; D007608:Kainic Acid