Allosteric regulation of the binding of [3H]acetylcholine to m2 muscarinic receptors

Gnagey, A.L.; Ellis, John E.

doi:10.1016/s0006-2952(96)00598-9

Cited by 25 publications

(14 citation statements)

References 19 publications

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“…Data points were usually measured in duplicate. CHO cell membranes do not possess cholinesterase activity (Lazareno and Birdsall, 1993;Gnagey and Ellis, 1996), so ACh could be used in the absence of a cholinesterase inhibitor. In some […”

Section: Methodsmentioning

confidence: 99%

Thiochrome Enhances Acetylcholine Affinity at Muscarinic M₄Receptors: Receptor Subtype Selectivity via Cooperativity Rather than Affinity

Lazareno

Doležal²,

Popham³

et al. 2004

Mol Pharmacol

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Thiochrome (2,7-dimethyl-5H-thiachromine-8-ethanol), an oxidation product and metabolite of thiamine, has little effect on the equilibrium binding of L-[ 3 3 H]ACh from potassium-stimulated slices of rat striatum, which contain autoinhibitory presynaptic M 4 receptors, but not from hippocampal slices, which contain presynaptic M 2 receptors. We conclude that thiochrome is a selective M 4 muscarinic receptor enhancer of ACh affinity and has neutral cooperativity with ACh at M 1 to M 3 receptors; it therefore demonstrates a powerful new form of selectivity, "absolute subtype selectivity", which is derived from cooperativity rather than from affinity.Most receptor-active ligands bind to the same site as the endogenous ligand, the so-called orthosteric site. Agonists mimic the actions of the endogenous ligand, whereas antagonists physically prevent the endogenous ligand from binding but lack its actions. The property of a ligand that determines its effect when bound to a receptor is called its efficacy. Different degrees of efficacy lead to so-called full agonists, partial agonists with a smaller maximal effect than full agonists; neutral antagonists, which occupy the active site without exerting any effect; and inverse agonists, which reduce the activity of constitutively active receptors (Kenakin, 2002). The selectivity of an orthosteric ligand for one receptor or receptor subtype is determined by its affinity for the receptor and its efficacy at that receptor. The difference in affinity between the target receptor and other receptors must be large for an orthosteric ligand to have useful selectivity. This can be difficult to achieve for receptors that show close homology at the orthosteric binding region such as the five subtypes of muscarinic receptor (M 1 -M 5 ) (Hulme et al., 1990). Selectivity derived from efficacy can also be hard to achieve, because the effect of a partial agonist depends on properties of the tissue, such as receptor density and downstream amplification mechanisms, which vary between cells and tissues, so a ligand with no apparent functional effect on tissues in vitro may nevertheless activate tissues in vivo, leading to unacceptable side effects (Terry et al., 2002).An alternative approach for developing selective ligands is to look for allosteric ligands that bind to a site on the receptor which is different from the site to which the endogenous ligand binds. This allows both types of ligand to bind simultaneously. If the affinity (or efficacy) of the endogenous ligand is different when it is bound to the allosteric liganded receptor compared with when it is bound to the free receptor, then the allosteric ligand exhibits positive or negative coop-

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Section: Methodsmentioning

confidence: 99%

Thiochrome Enhances Acetylcholine Affinity at Muscarinic M₄Receptors: Receptor Subtype Selectivity via Cooperativity Rather than Affinity

Lazareno

Doležal²,

Popham³

et al. 2004

Mol Pharmacol

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“…To note, CHO cell membranes do not possess cholinesterase activity (Gnagey et al, 1996) and acetylcholine could therefore be used in the absence of a cholinesterase inhibitor.…”

Section: Western Blot Analysismentioning

confidence: 99%

3-iodothyronamine (T1AM), a novel antagonist of muscarinic receptors

Laurino

Matucci

Vistoli

et al. 2016

European Journal of Pharmacology

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Abstract3-iodothyronamine (T1AM) is a trace amine suspected to derive from thyroid hormone metabolism. T1AM was described as a ligand of G-protein coupled monoaminergic receptors, including trace amine associated receptors, suggesting the amine may exert a modulatory role on the monoaminergic transmission. Nothing is known on the possibility that T1AM could also modulate the cholinergic transmission interacting with muscarinic receptors.We evaluated whether T1AM (10 nM-100 M) was able to i) displace T1AM recognized all muscarinic receptor subtypes (pKi values in the micromolar range). Interacting at type 3, T1AM reduced acetylcholine-increased pERK 1/2 levels. T1AM reduced carbachol-induced contraction of the rat urinary bladder. The fenoxyl residue and the iodide ion were found essential for establishing contacts with the active site of the rat muscarinic type 3 receptor subtype.Our results indicate that T1AM binds at muscarinic receptors behaving as a weak, not selective, antagonist. This finding adds knowledge on the pharmacodynamics features of T1AM and it may prompt investigation on novel pharmacological effects of T1AM at 3 conditions of hyper-activation of the muscarinic tone including the overactive urinary bladder.

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“…Data points were usually measured in duplicate. Chinese hamster ovary cell membranes do not possess cholinesterase activity (Lazareno and Birdsall, 1993;Gnagey and Ellis, 1996) so ACh could be used in the absence of a cholinesterase inhibitor. The test compounds were dissolved in dimethyl sulfoxide, which, at the highest final concentration of 2%, had no effect on binding.…”

Section: Materials [mentioning

confidence: 99%

Analogs of WIN 62,577 Define a Second Allosteric Site on Muscarinic Receptors

2002

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WIN 51,pyrimido [1,2-a] 3 H]NMS dissociation from M 3 receptors indicate that PG987 binds reversibly to a site distinct from that to which gallamine and strychnine bind: in contrast, PG987 seems to bind to the same site on M 3 receptors as KT5720, staurosporine, and WIN 51,708. Therefore, in addition to the allosteric site that binds strychnine (and probably chloromethyl brucine, another allosteric enhancer) there is a second, nonoverlapping, pharmacologically distinct allosteric site on M 3 receptors that also supports positive cooperativity with ACh.

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Allosteric regulation of the binding of [3H]acetylcholine to m2 muscarinic receptors

Cited by 25 publications

References 19 publications

Thiochrome Enhances Acetylcholine Affinity at Muscarinic M₄Receptors: Receptor Subtype Selectivity via Cooperativity Rather than Affinity

Thiochrome Enhances Acetylcholine Affinity at Muscarinic M₄Receptors: Receptor Subtype Selectivity via Cooperativity Rather than Affinity

3-iodothyronamine (T1AM), a novel antagonist of muscarinic receptors

Analogs of WIN 62,577 Define a Second Allosteric Site on Muscarinic Receptors

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Allosteric regulation of the binding of [3H]acetylcholine to m2 muscarinic receptors

Cited by 25 publications

References 19 publications

Thiochrome Enhances Acetylcholine Affinity at Muscarinic M4Receptors: Receptor Subtype Selectivity via Cooperativity Rather than Affinity

Thiochrome Enhances Acetylcholine Affinity at Muscarinic M4Receptors: Receptor Subtype Selectivity via Cooperativity Rather than Affinity

3-iodothyronamine (T1AM), a novel antagonist of muscarinic receptors

Analogs of WIN 62,577 Define a Second Allosteric Site on Muscarinic Receptors

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Thiochrome Enhances Acetylcholine Affinity at Muscarinic M₄Receptors: Receptor Subtype Selectivity via Cooperativity Rather than Affinity

Thiochrome Enhances Acetylcholine Affinity at Muscarinic M₄Receptors: Receptor Subtype Selectivity via Cooperativity Rather than Affinity