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Query: UNIPROT:P06889 (Mol)
 630,302 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The abilities of gallamine, obidoxime, tetrahydroaminoacridine (THA), and 8-(N,N-diethylamino)octyl-3,4,5-trimethoxybenzoate (TMB-8) to alter the rate of dissociation of N-[3H]methylscopolamine from rat cardiac muscarinic receptors were investigated. All four ligands monotonically slowed the dissociation, with the order of potency gallamine > TMB-8 > THA > obidoxime. There was a dramatic difference in the efficacy of these allosteric modulators. Gallamine, TMB-8, and THA slowed the dissociation of N-methylscopolamine by > 90% at maximally effective concentrations, whereas obidoxime was capable of slowing it by only about 50%. In a manner analogous to the action of a partial agonist, obidoxime was able to partially reverse the effects of the other three modulators. Furthermore, the concentration-dependent effects of combinations of obidoxime and gallamine were in good agreement with the model of competitive interaction between these two ligands. These results provide the first evidence that two muscarinic allosteric modulators interact competitively at a well defined site.
Mol Pharmacol 1992 Oct
PMID:Two allosteric modulators interact at a common site on cardiac muscarinic receptors. 143 41

Whereas classic muscarinic antagonist ligands appear to recognize only a single class of muscarinic receptor sites, the recently discovered antagonist pirenzepine appears to distinguish at least two classes of sites. Its unique binding properties, demonstrated in both indirect and direct binding studies, have led to an emerging concept of high affinity (M1) and low affinity (M2) sites. This concept has been supported by pharmacologic studies of functional muscarinic responses, as well as by data suggesting different effector relationships for the two sites. Gallamine possesses muscarinic antagonist properties, and it also recognizes heterogeneity among muscarinic receptors. The purpose of this study was to define gallamine-recognized heterogeneity in terms of the pirenzepine-defined M1, M2 concept. This has been done by studying the ability of gallamine to inhibit [3H]pirenzepine binding to the M1 site, and to inhibit [3H]quinuclidinylbenzilate ([3H]QNB) binding in cerebellar membrane preparations, which contain almost exclusively the M2 site. The results show that gallamine binds with high affinity to the M2 site, with Ki = 2.4 nM, and lower affinity to the M1 site with Ki = 24 nM. Within these classes gallamine does not recognize heterogeneity. The ability of gallamine to inhibit [3H]QNB binding to cortex is best described by a two-site model comprised of 77% low affinity gallamine sites (M1) and 23% high affinity gallamine sites (M2). Thus, the heterogeneity among muscarinic receptors which is recognized by gallamine within the receptor binding paradigms of this study can be attributed to the M1, M2 subtypes as defined by pirenzepine binding. In addition, gallamine at low concentrations appears to bind as a pure competitive antagonist at these two sites, indicated by linear Schild plots with slopes of 1.0, the lack of an effect on dissociation of radioligands, and the ability to protect [3H]pirenzepine and [3H]QNB-binding sites from alkylation by propylbenzylcholine mustard. These studies do not exclude the possibility of a non-competitive interaction of gallamine with the muscarinic receptor observed by other investigators at high gallamine concentrations, and postulated to occur at a site adjacent to the primary muscarinic site. It is proposed that gallamine is capable of interacting with both the primary muscarinic site and an allosteric site. These results support the emerging concept of M1 and M2 muscarinic subclasses and suggest that gallamine and related compounds may be useful in defining muscarinic receptor subclasses, given their higher affinity for the M2 site.
Mol Pharmacol 1986 Jul
PMID:Gallamine binding to muscarinic M1 and M2 receptors, studied by inhibition of [3H]pirenzepine and [3H]quinuclidinylbenzilate binding to rat brain membranes. 375 17

The binding of [3H]quinuclidinyl benzilate ([3H]QNB) to cardiac muscarinic receptors was inhibited not only by classical muscarinic antagonists but also by nicotinic blocking agents and inhibitors of acetylcholinesterase. Gallamine, pancuronium, ambenonium, and decamethonium were the most potent of these agents examined. All of the nicotinic antagonists with significant muscarinic receptor activity had two or three quaternary nitrogens, and the potency of a series of these compounds was a function of the distance between quaternary nitrogens. The effects of gallamine and pancuronium were studied in detail because these neuromuscular blocking agents showed heterogeneity in their binding to cardiac muscarinic receptors, whereas classical muscarinic antagonists such as QNB and atropine did not. Gallamine did not compete for all of the [3H]QNB binding sites on atrial membranes, but left at least 20% of [3H]QNB binding unaffected. Curves of pancuronium competition for [3H]QNB binding were shallow, consistent with two binding sites for pancuronium, with approximately 20% having low affinity. Additionally, in the presence of gallamine or pancuronium, [3H]QNB binding sites were no longer homogeneous, and Scatchard plots became nonlinear. Guanine nucleotides did not alter the effect of gallamine or pancuronium on [3H]QNB binding. Gallamine and pancuronium showed no agonist activity but, like atropine, completely antagonized muscarinic receptor-mediated inhibition of cyclic AMP formation. However, differences in the behavior of gallamine and atropine suggested that gallamine was not a purely competitive antagonist. Gallamine did not protect against receptor alkylation by propylbenzilylcholine mustard, and [3H]QNB dissociation was apparently slowed by gallamine. We interpret our data to suggest that gallamine not only competes for [3H]QNB binding sites, but also binds at a secondary site on the receptor, forming a ternary complex with [3H]QNB. Heterogeneity in ligand binding is proposed to result from the dual actions of gallamine and pancuronium as ligands at both primary and secondary sites on the cardiac muscarinic receptor.
Mol Pharmacol 1983 Jul
PMID:Heterogeneity of binding sites on cardiac muscarinic receptors induced by the neuromuscular blocking agents gallamine and pancuronium. 613 50

The interaction of gallamine with muscarinic receptors from different tissues has been investigated. Gallamine binds to a site distinct from the conventional muscarinic ligand binding site and modulates the binding of agonists and antagonists to the conventional binding site. In agreement with reported pharmacological studies, the effects of gallamine on the binding of muscarinic ligands are much greater in heart than in other tissues. These findings suggest the possibility of developing novel and selective muscarinic drugs.
Mol Pharmacol 1983 May
PMID:Modification of the binding properties of muscarinic receptors by gallamine. 686 5

We studied the ability of four nondepolarizing neuromuscular blocking agents (atracurium, gallamine, metocurine, and pancuronium) to act as competitive antagonists at mouse adult- and fetal-type muscle nictinic receptors. Receptor subunits for the fetal type (alpha, beta, gamma, and delta) and adult-type (alpha, beta, epsilon, and delta) receptors were stably expressed in quail fibroblasts. Binding for each drug was determined by the ability of the agents to reduce the initial rate of labeled alpha-bungarotoxin binding, and functional consequences were determined with the use of voltage-clamp studies of their ability to elicit currents or to block currents elicited by acetylcholine. Each agent has a different affinity for the two acetylcholine-binding sites on a single receptor; the rank order of affinities is the same for both fetal- and adult-type receptors. All agents inhibited activation of adult-type receptors by ACh, consistent with the idea that occupation of either the high or low affinity site completely blocks activation when acetylcholine binds to the other site on the receptor. The concentration dependence of the inhibition of acetylcholine-elicited current was predictable from the affinities estimated from independent measurements of the inhibition of alpha-bungarotoxin binding. Gallamine and pancuronium also acted as competitive inhibitors of fetal-type receptors, and, again, the concentration dependence of the inhibition was predictable from binding data. However, metocurine and atracurium could potentiate the responses of fetal-type receptors to low concentrations of acetylcholine. The interaction of metocurine and atracurium with acetylcholine at fetal-type receptors could be accounted for by a weak partial agonist activity. It has been suggested that some pairs of nondepolarizing neuromuscular blocking agents might be more efficacious because the high affinity site for one agent might be the low affinity site for another. This hypothesis was tested for the pair of agents metocurine and gallamine by determining the ability of a mixture of agents to inhibit the binding of alpha-bungarotoxin. The results are consistent with the idea that both metocurine and gallamine have a high affinity for the same site on the receptor. The ability of gallamine to block the partial agonist action of metocurine at fetal-type receptors was tested as well and also indicated that both agents share the same high affinity site.
Mol Pharmacol 1996 May
PMID:Ability of nondepolarizing neuromuscular blocking drugs to act as partial agonists at fetal and adult mouse muscle nicotinic receptors. 862 44

Gallamine allosterically modulates the binding of classical muscarinic ligands with a potency order of M(2) > M(1),M(4) > M(3), M(5). We have suggested previously that the M(2)/M(5) and M(2)/M(3) selectivities are attributable to an epitope in the sixth transmembrane region or third outer loop (o3) region of the receptor. In this study, analysis of numerous point mutations in this region of the M(5) receptor found that a mutation of V --> N resulted in an increased affinity toward gallamine, suggesting that the asparagine residue at M(2)(419) is responsible for gallamine's M(2)/M(5) selectivity. Mutations in the other subtypes indicated that the acidic residues found at this position in M(1) and M(4) are associated with slightly higher affinity toward gallamine, whereas the valine and lysine residues of M(5) and M(3), respectively, are associated with significantly lower affinity. In the o2 region, replacement of an acidic sequence of M(2) (EDGE) by the corresponding neutral sequence of M(1) (LAGQ) reduced the affinity toward gallamine, as reported previously by others; the converse substitution of the acidic sequence into M(1) significantly increased affinity for gallamine. Substitution of the M(1) sequence into this region of M(5) markedly reduced affinity toward gallamine, whereas substitution into M(4) had no effect. All of the above mutations are consistent with gallamine binding with a similar orientation at each subtype, such that it interacts with acidic residues in the o2 region of M(3) and M(5) and with acidic residues in the o3 region of M(1) and M(4); gallamine appears to interact with both regions of the M(2) subtype.
Mol Pharmacol 1999 Dec
PMID:Site-directed mutagenesis reveals two epitopes involved in the subtype selectivity of the allosteric interactions of gallamine at muscarinic acetylcholine receptors. 1057 52

The M(2) muscarinic receptor has two topographically distinct sites: the orthosteric site and an allosteric site recognized by compounds such as gallamine. It also can exhibit cooperative effects in the binding of orthosteric ligands, presumably to the orthosteric sites within an oligomer. Such effects would be difficult to interpret, however, if those ligands also bound to the allosteric site. Monomers of the hemagglutinin (HA)- and FLAG-tagged human M(2) receptor therefore have been purified from coinfected Sf9 cells and examined for any effect of the antagonist N-methyl scopolamine or the agonist oxotremorine-M on the rate at which N-[(3)H]methyl scopolamine dissociates from the orthosteric site (k(obsd)). The predominantly monomeric status was confirmed by coimmunoprecipitation and by cross-linking with bis(sulfosuccinimidyl)suberate. Both N-methyl scopolamine and oxotremorine-M acted in a cooperative manner to decrease k(obsd) by 4.5- and 9.1-fold, respectively; the corresponding estimates of affinity (log K(L)) are -2.55 +/- 0.13 and -2.29 +/- 0.14. Gallamine and the allosteric ligand obidoxime decreased k(obsd) by more than 100-fold (log K(L) = -4.12 +/- 0.04) and by only 1.1-fold (log K(L) = -1.73 +/- 0.91), respectively. Obidoxime reversed the effect of N-methyl scopolamine, oxotremorine-M, and gallamine in a manner that could be described by a model in which all four ligands compete for a common allosteric site. Ligands generally assumed to be exclusively orthosteric therefore can act at the allosteric site of the M(2) receptor, albeit at comparatively high concentrations.
Mol Pharmacol 2008 Sep
PMID:Binding of orthosteric ligands to the allosteric site of the M(2) muscarinic cholinergic receptor. 1858 53