Limpet_Chicken
Bluelighter
- Joined
- Oct 13, 2005
- Messages
- 6,323
This came up after a PM from an individual curious about getting on it, came to me with a few questions, but appeared to think it more or less alpha1 selective, but AFAIK, it isn't. Just did some digging, and found some data specifically stating that the binding site was separate from bicucculline, and akin to that of picrotoxin.
Bicucculline is alpha1-selective, or at least has affinity for a1 type BZD receptors does it not? and in a paper on loreclezole, it stated that it (chlormethiazole) displaced neither GABA, muscimol, nor bicucculline from their respective binding sites in a competitive binding assay. But stated that it was competitive with the alkyl-bicyclophosphorothionate convulsants. I'm not overly familar with these, at least, not to the extent of knowing their molecular mode of action, only that they are potent GABAa antagonists.
One paper, this one
http://sci-hub.tw/10.1016/0014-2999(89)90242-2
Suggests that it might act at a unique binding site, and specifically states that this is different from the barbiturate binding site. I'd always been under the impression that the barbiturate site of GABAaRs was synonymous with the picrotoxin-labeled binding site, and that the two were competitive ligands vs one another.
Yet the paper quoted, it states that chlormethiazole did not affect the binding time of tritiated flunitrazepam enhanced via (3H)pentobarbital. Although it did display some displacement of (3H)flunitrazepam, although this looks odd, given the typical therapeutic dose of chlormethiazole when used as a hypnotic, some
(125-185 uMol), it doesn't ACT like a benzo site ligand, and it's sensitivity to displacement by picrotoxin or dihydropicrotoxinin suggest that it isn't. Subjectively, it doesn't feel a damn bit like a benzo, more like a very, very clean barbiturate (using as subjective comparators, barbital, various benzos, nitrazepam,diazepam, lorazepam, loprazolam and a fair few others.), and besides, a benzo OD is most unlikely to be lethal, chlormethiazole is meant to be pretty good at knocking people off.
The quoted paper shows it's doing some rather weird shit, when it comes to interacting with tert-butylbicyclophosphorothionate (one of the 'cage convulsants', a potent GABAa antagonist)
Whereas pentobarbital inhibited the binding Bmax of TBPS, it did very little to alter the dissociation constant of TBPS, when used alone, compared control, substrate being rat synaptosomes, whereas chlormethiazole, whereas chlormethiazole significantly increased the dissociation constant of TBPS whilst the Bmax was left almost unaltered.
What the devil is going on here? The conclusion was that the barb site, benzo site, orthosteric (muscimol) and neurosteroid binding sites are not the target. And that it alters TBPS binding not by taking up binding sites, but by modulating the Kd of the antagonist ligand. Which suggests an allosteric ligand does it not (in the case of chlormethiazole) but induction of direct uptake of radiolabelled chloride ions suggests something like a channel opener, no?
Bicucculline is alpha1-selective, or at least has affinity for a1 type BZD receptors does it not? and in a paper on loreclezole, it stated that it (chlormethiazole) displaced neither GABA, muscimol, nor bicucculline from their respective binding sites in a competitive binding assay. But stated that it was competitive with the alkyl-bicyclophosphorothionate convulsants. I'm not overly familar with these, at least, not to the extent of knowing their molecular mode of action, only that they are potent GABAa antagonists.
One paper, this one
http://sci-hub.tw/10.1016/0014-2999(89)90242-2
Suggests that it might act at a unique binding site, and specifically states that this is different from the barbiturate binding site. I'd always been under the impression that the barbiturate site of GABAaRs was synonymous with the picrotoxin-labeled binding site, and that the two were competitive ligands vs one another.
Yet the paper quoted, it states that chlormethiazole did not affect the binding time of tritiated flunitrazepam enhanced via (3H)pentobarbital. Although it did display some displacement of (3H)flunitrazepam, although this looks odd, given the typical therapeutic dose of chlormethiazole when used as a hypnotic, some
(125-185 uMol), it doesn't ACT like a benzo site ligand, and it's sensitivity to displacement by picrotoxin or dihydropicrotoxinin suggest that it isn't. Subjectively, it doesn't feel a damn bit like a benzo, more like a very, very clean barbiturate (using as subjective comparators, barbital, various benzos, nitrazepam,diazepam, lorazepam, loprazolam and a fair few others.), and besides, a benzo OD is most unlikely to be lethal, chlormethiazole is meant to be pretty good at knocking people off.
The quoted paper shows it's doing some rather weird shit, when it comes to interacting with tert-butylbicyclophosphorothionate (one of the 'cage convulsants', a potent GABAa antagonist)
Whereas pentobarbital inhibited the binding Bmax of TBPS, it did very little to alter the dissociation constant of TBPS, when used alone, compared control, substrate being rat synaptosomes, whereas chlormethiazole, whereas chlormethiazole significantly increased the dissociation constant of TBPS whilst the Bmax was left almost unaltered.
What the devil is going on here? The conclusion was that the barb site, benzo site, orthosteric (muscimol) and neurosteroid binding sites are not the target. And that it alters TBPS binding not by taking up binding sites, but by modulating the Kd of the antagonist ligand. Which suggests an allosteric ligand does it not (in the case of chlormethiazole) but induction of direct uptake of radiolabelled chloride ions suggests something like a channel opener, no?