An allosteric modulator is a ligand that binds to an allosteric site on the receptor and changes receptor conformation to produce increase (positive cooperativity) or decrease (negative cooperativity) in the binding or action of an orthosteric agonist (e.g., acetylcholine). Since the identification of gallamine as the first allosteric modulator of muscarinic receptors in 1976, this unique mode of receptor modulation has been intensively studied by many groups. This review summarizes over 30 years of research on the molecular mechanisms of allosteric interactions of drugs with the receptor and for new allosteric modulators of muscarinic receptors with potential therapeutic use. Identification of positive modulators of acetylcholine binding and function that enhance neurotransmission and the discovery of highly selective allosteric modulators are mile-stones on the way to novel therapeutic agents for the treatment of schizophrenia, Alzheimer's disease and other disorders involving impaired cognitive function.

• Klíčová slova
• Alzheimer’s disease, allosteric modulation, muscarinic acetylcholine receptors, schizophrenia,
• Publikační typ
• časopisecké články MeSH
• přehledy MeSH

Allosteric enhancement of the affinity of muscarinic receptors for their ligands offers a new way to influence cholinergic neurotransmission. The structure of the allosteric binding domain(s) and the features of agonists, antagonists and modulators which determine the occurrence of either positive or negative cooperativity require clarification. We tested interactions between allosteric modulators alcuronium, strychnine and brucine and eight antagonists at muscarinic receptors expressed in CHO cells. In experiments with unlabeled antagonists, all three modulators enhanced the affinity for 4-diphenylacetoxy-N-dimethylpiperidinium (4-DAMP) at the M2 receptors, and strychnine did so also at the M4 receptors. Positive interactions were also observed between alcuronium and L-hyoscyamine (M2) and scopolamine (M2), between strychnine and butylscopolamine (M4), L-hyoscyamine (M2 and M4) and scopolamine (M4), and between brucine and scopolamine (M2). Positive effects of alcuronium, strychnine and brucine on the affinity of the M2 receptors for 4-DAMP have been confirmed by direct measurements of the binding of [3H]-4-DAMP. A comparison of molecular models of several antagonists which are esters revealed that antagonists in which the distance between the N and the carboxyl C atoms corresponds to five chemical bonds are more likely to display positive cooperativity with alcuronium at the M2 receptors than the antagonists in which the N-carboxyl C distance corresponds to four chemical bonds.

• MeSH
• alkuronium farmakologie   MeSH
• alosterická regulace MeSH
• antagonisté muskarinových receptorů chemie   farmakologie   MeSH
• CHO buňky MeSH
• křečci praví MeSH
• N-methylskopolamin metabolismus   MeSH
• piperidiny farmakologie   MeSH
• radioligandová zkouška MeSH
• strychnin analogy a deriváty   farmakologie   MeSH
• tritium MeSH
• zvířata MeSH
• Check Tag
• křečci praví MeSH
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• 4-diphenylacetoxy-1,1-dimethylpiperidinium MeSH Prohlížeč
• alkuronium MeSH
• antagonisté muskarinových receptorů MeSH
• brucine MeSH Prohlížeč
• N-methylskopolamin MeSH
• piperidiny MeSH
• strychnin MeSH
• tritium MeSH

Seven esters of alpha-truxillic acid have been synthesized: bis-3-piperidylpropyl ester and its quaternary bis-N-ethyl derivative, bis-N-diethylaminopropyl ester and its quaternary bis-N-methyl derivative, and bis-4-piperidylbutyl ester and its quaternary bis-N-methyl and bis-N-ethyl derivatives. All esters inhibited the specific binding of muscarinic receptor antagonist [methyl-3H]-N-methylscopolamine ([3H]-NMS) to muscarinic receptors in membranes of CHO cell lines stably expressing the human gene for the M1, M2, M3 or M4 subtype of muscarinic receptors. All esters displayed the highest potency at the M2 and the lowest potency at the M3 receptor subtype. In experiments performed on the M2 muscarinic receptor subtype, the affinity between the receptors and the esters was greatly increased when the concentration of ions was diminished. The highest affinities were found for the tertiary bis-3-piperidylpropyl and bis-4-piperidylbutyl aminoesters (equilibrium dissociation constants of 52 and 179 pM, respectively, in the low ionic strength medium). All investigated esters slowed down the dissociation of [3H]-NMS from the M2 muscarinic receptor subtype. [3H]-NMS dissociation from the M1, M3 and M4 muscarinic receptor subtypes was investigated in experiments with the bis-4-piperidylbutyl aminoester and also found to be decelerated. It is concluded that the esters of alpha-truxillic acid act as M2-selective allosteric modulators of muscarinic receptors and that, by their potency, the tertiary bis-3-piperidylpropyl and bis-4-piperidylbutyl aminoesters surpass the other known allosteric modulators of these receptors.

• MeSH
• alosterická regulace MeSH
• antagonisté muskarinových receptorů metabolismus   farmakologie   MeSH
• CHO buňky MeSH
• cyklobutany farmakologie   MeSH
• křečci praví MeSH
• lidé MeSH
• N-methylskopolamin metabolismus   MeSH
• receptory muskarinové klasifikace   účinky léků   MeSH
• tritium MeSH
• zvířata MeSH
• Check Tag
• křečci praví MeSH
• lidé MeSH
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Research Support, U.S. Gov't, P.H.S. MeSH
• Názvy látek
• antagonisté muskarinových receptorů MeSH
• cyklobutany MeSH
• N-methylskopolamin MeSH
• receptory muskarinové MeSH
• tritium MeSH
• truxillic acid MeSH Prohlížeč

Ligands that bind to the allosteric-binding sites on muscarinic acetylcholine receptors alter the conformation of the classical-binding sites of these receptors and either diminish or increase their affinity for muscarinic agonists and classical antagonists. It is not known whether the resulting conformational change also affects the interaction between the receptors and the G proteins. We have now found that the muscarinic receptor allosteric modulators alcuronium, gallamine, and strychnine (acting in the absence of an agonist) alter the synthesis of cAMP in Chinese hamster ovary (CHO) cells expressing the M2 or the M4 subtype of muscarinic receptors in the same direction as the agonist carbachol. In addition, most of their effects on the production of inositol phosphates in CHO cells expressing the M1 or the M3 muscarinic receptor subtypes are also similar to (although much weaker than) those of carbachol. The agonist-like effects of the allosteric modulators are not observed in CHO cells that have not been transfected with the gene for any of the subtypes of muscarinic receptors. The effects of alcuronium on the formation of cAMP and inositol phosphates are not prevented by the classical muscarinic antagonist quinuclidinyl benzilate. These observations demonstrate for the first time that the G protein-mediated functional responses of muscarinic receptors can be evoked not only from their classical, but also from their allosteric, binding sites. This represents a new mechanism of receptor activation.

• MeSH
• agonisté muskarinových receptorů farmakologie   MeSH
• alkuronium farmakologie   MeSH
• alosterická regulace MeSH
• AMP cyklický metabolismus   MeSH
• antagonisté muskarinových receptorů farmakologie   MeSH
• chinuklidinylbenzilát farmakologie   MeSH
• CHO buňky MeSH
• inositolfosfáty fyziologie   MeSH
• křečci praví MeSH
• periodicita MeSH
• proteiny vázající GTP fyziologie   MeSH
• receptory muskarinové fyziologie   MeSH
• rekombinantní proteiny MeSH
• signální transdukce MeSH
• strychnin farmakologie   MeSH
• transfekce MeSH
• triethojodid gallaminia farmakologie   MeSH
• zvířata MeSH
• Check Tag
• křečci praví MeSH
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Research Support, U.S. Gov't, P.H.S. MeSH
• Názvy látek
• agonisté muskarinových receptorů MeSH
• alkuronium MeSH
• AMP cyklický MeSH
• antagonisté muskarinových receptorů MeSH
• chinuklidinylbenzilát MeSH
• inositolfosfáty MeSH
• proteiny vázající GTP MeSH
• receptory muskarinové MeSH
• rekombinantní proteiny MeSH
• strychnin MeSH
• triethojodid gallaminia MeSH

1. By measuring the binding of N-[3H-methyl]-scopolamine ([3H]-NMS) and of unlabelled subtype-specific muscarinic antagonists, two populations of muscarinic binding sites can be distinguished in the membranes of cardiac ventricles taken from 1-day-old chicks. One of them, corresponding to approximately 80% of [3H]-NMS binding sites, has higher affinities for AF-DX116 (pKi = 6.42) and methoctramine (pKi = 7.33); the rate of [3H]NMS dissociation from these sites is fast. The other population, corresponding to approximately 20% of [3H]-NMS binding sites, has lower affinities for AF-DX116 (pKi = 5.00) and methoctramine (pKi = 6.19); the rate of [3H]-NMS dissociation from these sites is slow. Both populations have high affinities for pirenzepine, but the affinity of the former (major) population is lower (pKi = 7.99) than that of the latter (minor) population (pKi = 10.14). 2. Since it has been shown earlier that two mRNAs for muscarinic receptors are expressed in the chick heart, one of them close to the genetically defined m2 and the other to the m4 subtype, we propose that the major population of binding sites with high affinities for AF-DX116 and methoctramine and the lower affinity for pirenzepine represents the M2-like receptors, while the minor population represents the M4-like receptors. 3. It proved possible to obtain isolated samples of either population by selectively protecting the M2-like sites with AF-DX116 and the M4-like sites with pirenzepine, and by inactivating the unprotected sites with benzilylcholine mustard. The properties of the isolated populations corresponded to those derived from the analysis of [3H]-NMS binding to the original mixed population.4 Alcuronium exerted positive allosteric action on the binding of [3H]-NMS both to the M2-like and the M4-like population and severely slowed down [3H]-NMS dissociation from them; its affinity for the M2-like sites was 3-10 times higher.

• MeSH
• alkuronium farmakokinetika   MeSH
• antagonisté muskarinových receptorů * MeSH
• cholin analogy a deriváty   MeSH
• cholinergní látky MeSH
• diaminy farmakokinetika   MeSH
• krysa rodu Rattus MeSH
• kur domácí MeSH
• ligandy MeSH
• messenger RNA metabolismus   MeSH
• myokard metabolismus   MeSH
• N-methylskopolamin MeSH
• parasympatolytika farmakologie   MeSH
• pirenzepin analogy a deriváty   farmakokinetika   MeSH
• potkani Wistar MeSH
• radioligandová zkouška MeSH
• receptory muskarinové metabolismus   MeSH
• skopolaminové deriváty farmakokinetika   MeSH
• techniky in vitro MeSH
• zvířata MeSH
• Check Tag
• krysa rodu Rattus MeSH
• mužské pohlaví MeSH
• ženské pohlaví MeSH
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• alkuronium MeSH
• antagonisté muskarinových receptorů * MeSH
• benzilylcholine mustard MeSH Prohlížeč
• cholin MeSH
• cholinergní látky MeSH
• diaminy MeSH
• ligandy MeSH
• messenger RNA MeSH
• methoctramine MeSH Prohlížeč
• N-methylskopolamin MeSH
• otenzepad MeSH Prohlížeč
• parasympatolytika MeSH
• pirenzepin MeSH
• receptory muskarinové MeSH
• skopolaminové deriváty MeSH