Dissociation constants and relative efficacies of acetylcholine, (+)‐ and (‐)‐methacholine at muscarinic receptors in the guinea‐pig ileum

Ringdahl, Björn

doi:10.1111/j.1476-5381.1986.tb11115.x

Cited by 18 publications

(24 citation statements)

References 15 publications

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“…Because GTP has opposite effects on observed affinity and intrinsic efficacy (Ehlert and Rathbun, 1990), a variation in the concentration of GTP should have little effect on the product of these two parameters and, hence, on the estimate of RA i . The estimates of the dissociation constants and relative efficacies of carbachol, oxotremorine, and oxotremorine-M in the M 2 KO mouse are similar to those estimated in the isolated guinea pig ileum (Ringdahl and Jenden, 1983;Ringdahl, 1984Ringdahl, , 1985. In addition, the RA i values of muscarinic agonists are consistent with those measured in the CHO hM 3 cell, except for McN-A-343.…”

Section: Agonist Activity and Active Receptor States 391supporting

confidence: 51%

Estimation of Relative Microscopic Affinity Constants of Agonists for the Active State of the Receptor in Functional Studies on M₂ and M₃ Muscarinic Receptors

Tran¹,

Chang²,

Matsui³

et al. 2008

Mol Pharmacol

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In prior work, we have shown that it is possible to estimate the product of observed affinity and intrinsic efficacy of an agonist expressed relative to that of a standard agonist simply through the analysis of their respective concentration-response curves. In this report, we show analytically and through mathematical modeling that this product, termed intrinsic relative activity (RA i ), is equivalent to the ratio of microscopic affinity constants of the agonists for the active state of the receptor. We also compared the RA i estimates of selected muscarinic agonists with a relative estimate of the product of observed affinity and intrinsic efficacy determined independently through the method of partial receptor inactivation. There was good agreement between these two estimates when agonist-mediated inhibition of forskolin-stimulated cAMP accumulation was measured in Chinese hamster ovary cells stably expressing the human M 2 muscarinic receptor. Likewise, there was good agreement between the two estimates when agonist activity was measured on the ileum from M 2 muscarinic receptor knockout mice, a convenient assay for M 3 receptor activity. The RA i estimates of agonists in the mouse ileum were similar to those estimated at the human M 3 receptor with the exception of 4-(m-chlorophenyl-carbamoyloxy)-2-butynyltrimethylammonium (McN-A-343), which is known to be an M 1 -and M 4 -selective muscarinic agonist. Additional experiments showed that the response to McN-A-343 in the mouse ileum included a non-M 3 muscarinic receptor component. Our results show that the RA i estimate is a useful receptor-dependent measure of agonist activity and ligand-directed signaling.Drug discovery often involves testing compounds in highthroughput screens to determine their activity at specific receptors. The process not only identifies useful drugs but also helps to explain how variation in the structure of a compound alters its pharmacological activity. With regard to agonists at G protein-coupled receptors (GPCRs), the most common measurements of functional activity are the maximal response (E max ) and the concentration of agonist required for half-maximal response (EC 50 ). These parameters can vary for the same agonist, however, depending on the coupling protein through which the receptor signals (e.g., G protein) and the nature of the response being measured. What is needed is a measure of agonist activity that is dependent solely on the agonist-receptor interaction and not on downstream elements in the signaling cascade.

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Section: Agonist Activity and Active Receptor States 391supporting

confidence: 51%

Estimation of Relative Microscopic Affinity Constants of Agonists for the Active State of the Receptor in Functional Studies on M₂ and M₃ Muscarinic Receptors

Tran¹,

Chang²,

Matsui³

et al. 2008

Mol Pharmacol

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“…A possible reason to doubt the validity of the use of alkylating agents is that these drugs, at high concentrations and when not removed from the biophase, may not only reduce the concentration of active receptors, but also in some way disturb the normal receptor-effector coupling mechanisms. However, the agonists affinity constants determined after fractional receptor inactivation (Furchgott, 1966) are very close to those determined according to a method not involving the use of alkylating agents (Waud, 1969) as confirmed by Parker (1972) and by Ringdahl (1984a) for muscarinic receptors in the intestinal smooth muscle, and by Ruffolo et al (1979) for a-adrenoceptors in rat aorta.…”

Section: Discussionmentioning

confidence: 88%

Affinity and efficacy of racemic, (+)‐, and (−)‐methacholine in muscarinic inhibition of [³H]‐noradrenaline release

Fuder

Jung

1985

British J Pharmacology

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Mackay (1966). KA of( + )-, (± )-, and (-)-methacholine were 2.5, 4 and 440 ZlM, resulting in an isomeric affinity ratio KA (+ )/KA (-) of 180.The discrepancy between the isomeric IC50 ratio and the isomeric KA ratio is explained by a higher intrinsic efficacy of the (+ )-enantiomer compared to the (-)-enantiomer. Thus, (+ )-methacholine has to occupy fewer receptors to induce a given inhibition of release than its antipode as revealed by a plot of fractional receptor occupancy vs response. 4 The results show that, in the effector system of presynaptic muscarinic inhibition, methacholine enantiomers differ greatly not only in affinity for the receptor, but also to some extent in the efficiency of signal transmission, and both parameters contribute to the high isomeric potency ratio. The activity of the racemate is fully accounted for by the activity of the (+)-enantiomer.

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“…This procedure required the availability of an irreversible receptor blocking agent, and has subsequently been applied to m-adrenoceptors (Besse & Furchgott, 1976), muscarinic receptors (Ringdahl, 1984) and P-adrenoceptor agonists (Broadley & Nicholson, 1978).…”

Section: Introductionmentioning

confidence: 99%

The determination of receptor constants for histamine H₂‐agonists in the guinea‐pig isolated right atrium using an irreversible H₂‐antagonist

Rising¹,

Steward²

1986

British J Pharmacology

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1 From measurements of chronotropy in the guinea-pig isolated right atrium, a compound (El 309) was found which behaved as an irreversible antagonist at the histamine H2 receptor. 2 E1309 was used to block irreversibly a proportion of the H2 receptors and the dissociation constants, relative efficacies and receptor reserves of four H2-agonists were determined.3 The calculated dissociation constants were similar to the Ki values reported from H2-radioligand binding studies but different from the observed ECm values.4 The order of potency for the four H2-agonists was impromidine > > histamine > dimaprit > 4-methylhistamine. 5 The order of relative efficacy was 4-methylhistamine > dimaprit > histamine > impromidine, the natural agonist not being the most efficacious. This atypical finding is discussed in relation to other receptor classes.

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Dissociation constants and relative efficacies of acetylcholine, (+)‐ and (‐)‐methacholine at muscarinic receptors in the guinea‐pig ileum

Cited by 18 publications

References 15 publications

Estimation of Relative Microscopic Affinity Constants of Agonists for the Active State of the Receptor in Functional Studies on M₂ and M₃ Muscarinic Receptors

Estimation of Relative Microscopic Affinity Constants of Agonists for the Active State of the Receptor in Functional Studies on M₂ and M₃ Muscarinic Receptors

Affinity and efficacy of racemic, (+)‐, and (−)‐methacholine in muscarinic inhibition of [³H]‐noradrenaline release

The determination of receptor constants for histamine H₂‐agonists in the guinea‐pig isolated right atrium using an irreversible H₂‐antagonist

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Dissociation constants and relative efficacies of acetylcholine, (+)‐ and (‐)‐methacholine at muscarinic receptors in the guinea‐pig ileum

Cited by 18 publications

References 15 publications

Estimation of Relative Microscopic Affinity Constants of Agonists for the Active State of the Receptor in Functional Studies on M2 and M3 Muscarinic Receptors

Estimation of Relative Microscopic Affinity Constants of Agonists for the Active State of the Receptor in Functional Studies on M2 and M3 Muscarinic Receptors

Affinity and efficacy of racemic, (+)‐, and (−)‐methacholine in muscarinic inhibition of [3H]‐noradrenaline release

The determination of receptor constants for histamine H2‐agonists in the guinea‐pig isolated right atrium using an irreversible H2‐antagonist

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Estimation of Relative Microscopic Affinity Constants of Agonists for the Active State of the Receptor in Functional Studies on M₂ and M₃ Muscarinic Receptors

Estimation of Relative Microscopic Affinity Constants of Agonists for the Active State of the Receptor in Functional Studies on M₂ and M₃ Muscarinic Receptors

Affinity and efficacy of racemic, (+)‐, and (−)‐methacholine in muscarinic inhibition of [³H]‐noradrenaline release

The determination of receptor constants for histamine H₂‐agonists in the guinea‐pig isolated right atrium using an irreversible H₂‐antagonist