Binding of [3H]DMCM, a convulsive benzodiazepine ligand, to rat brain membranes: preliminary studies.
DMCM (methyl 6,7-dimethoxy-4-ethyl-beta-carboline-3-carboxylate) produces convulsions in mice and rats, probably by interacting with benzodiazepine (BZ) receptors. Investigation of specific binding of [3H]DMCM to rat hippocampus and cortex revealed polyphasic saturation curves, indicating a high-affinity site (KD = 0.5-0.8 nM) and a site with lower affinity (KD = 3-6 nM). BZ receptor ligands of various chemical classes, but not other agents, displace [3H]DMCM from specific binding sites--indicating that [3H]DMCM binds to BZ receptors in rat brain. The regional distribution of [3H]DMCM binding is complementary to that of the BZ1-selective radioligand [3H]PrCC. Specific binding of [3H]DMCM (0.1 nM) was reduced by gamma-aminobutyric acid (GABA) receptor agonist to approximately 20% of the control value at 37 degrees C in chloride-containing buffers; the reduction was bicuculline methiodide- and RU 5135-sensitive. The effective concentrations of 10 GABA analogues in reducing [3H]DMCM binding correlated closely to published values for their GABA receptor affinity. Specific binding of [3H]DMCM is regulated by unknown factors; e.g. enhanced binding was found by Ag+ treatment of membranes, in the presence of picrotoxinin, or by exposure to ultraviolet light in the presence of flunitrazepam. In conclusion, [3H]DMCM appears to bind to high-affinity brain BZ receptors, although the binding properties are different from those of [3H]flunitrazepam and [3H]PrCC. These differences might relate in part to subclass selectivity and in part to differences in efficacy of DMCM at BZ receptors.
D000818:Animals; D001569:Benzodiazepines / Q000378:metabolism*; D001667:Binding, Competitive; D001921:Brain / Q000378:metabolism*; D002243:Carbolines / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism; D003292:Convulsants / Q000378:metabolism*; D006624:Hippocampus / Q000378:metabolism; D007211:Indoles / Q000378:metabolism*; D007700:Kinetics; D051381:Rats; D011956:Receptors, Cell Surface / Q000378:metabolism*; D011963:Receptors, GABA-A; D013816:Thermodynamics; D014018:Tissue Distribution
D002243:Carbolines; D003292:Convulsants; D007211:Indoles; D011956:Receptors, Cell Surface; D011963:Receptors, GABA-A; D001569:Benzodiazepines; C034818:methyl 6,7-dimethoxy-4-ethyl-beta-carboline-3-carboxylate