An operational model of pharmacological agonism: the effect of E/[A] curve shape on agonist dissociation constant estimation

Black, J.W.; Leff, P.; Shankley, Nigel P.; Wood, JodiAnne T.

doi:10.1111/j.1476-5381.1985.tb12941.x

Cited by 277 publications

(211 citation statements)

References 14 publications

(21 reference statements)

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“…The 'Hill slopes' quoted in Figure 1 are necessarily approximate because, for n = 1, the E/[A] curve is not a logistic function (Black et al, 1985). The deviation from a logistic function is small, however, so it may reasonably be assumed that the gradient of the midpoint on the E/[A] curve is equal to the midpoint gradient of the logistic function best describing the E/[A] curve.…”

Section: Hill Slopes Of Agonist E/[a] Curvesmentioning

confidence: 99%

“…When t is large, Hill slope z n, but when T is small the Hill slope tends towards 1 (Black et al, 1985) so, for a given Hill slope, n;k Hill slope when T is big, and n increasingly deviates from 1 as T becomes smaller. The size of the deviation of the Cheng-Prusoff estimate as [A] -* 0 depends only on n and is independent of t (17), and it increases as n deviates from 1.…”

Section: Hill Slopes Of Agonist E/[a] Curvesmentioning

confidence: 99%

“…The deviation from a logistic function is small, however, so it may reasonably be assumed that the gradient of the midpoint on the E/[A] curve is equal to the midpoint gradient of the logistic function best describing the E/[A] curve. The midpoint gradient of a normalised E/log[A] curve generated by the operational model is (Black et al, 1985) 0.576.n. (2 + T?).…”

Section: Hill Slopes Of Agonist E/[a] Curvesmentioning

confidence: 99%

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Estimation of competitive antagonist affinity from functional inhibition curves using the Gaddum, Schild and Cheng‐Prusoíf equations

Lazareno

Birdsall

1993

British J Pharmacology

154

126

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1 The estimation of antagonist affinity from functional experiments in which the effect of a fixed agonist concentration is reduced by a range of antagonist concentrations ('functional inhibition curves') has been considered from both a theoretical and experimental viewpoint. 3 The usual procedure of applying the Cheng-Prusoff correction is shown to be theoretically invalid, and predictions are made of the size and distribution of errors associated with this procedure. 4 A different procedure for estimating antagonist affinity, using the principles of dose-ratio analysis and analogous to use of the Gaddum equation, is found to be accurate and theoretically valid. 5 A novel method of analysis allows accurate estimation of both antagonist affinity and Schild slope, by fitting the combined data from an antagonist inhibition curve and an agonist activation curve directly to a form of the Schild equation (derived by Waud) using non-linear regression analysis. 6 It is shown that the conventional Schild analysis can be enhanced by treating part of the data as a family of inhibition curves and including in the Schild plot dose-ratios estimated from the inhibition curves.

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Section: Hill Slopes Of Agonist E/[a] Curvesmentioning

confidence: 99%

Section: Hill Slopes Of Agonist E/[a] Curvesmentioning

confidence: 99%

Section: Hill Slopes Of Agonist E/[a] Curvesmentioning

confidence: 99%

See 1 more Smart Citation

Estimation of competitive antagonist affinity from functional inhibition curves using the Gaddum, Schild and Cheng‐Prusoíf equations

Lazareno

Birdsall

1993

British J Pharmacology

154

126

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“…Alternatively, the values for both doseresponse curves (before and after block) obtained with a full agonist may be used to calculate the common values of M, Kd and P as well as the individual value of T for each curve. This procedure (referred to as 'B2') was followed by Black et al (1985) and in the later part of this work the experimental data have been analysed in both ways, as well as by the null method. As can be seen in Figure 1 there is usually little difference between the fit obtained with 'BI' and 'B2'.…”

Section: Guinea-pig Isolated Ileummentioning

confidence: 99%

“…With the 'operational' model (Black & Leff, 1983) it is possible to write an equation relating response to dose for the two curves (see below). From a comparison of estimates of the affinity of 5-hydroxytryptamine for receptors on rabbit aorta calculated by the 'operational model' and the 'null method ', Black et al (1985) concluded that 'the model provided an estimate of KA which was not significantly different from the estimate obtained using Furchgott's null method'. But although the mean estimates of log K were very similar (6.95 and 6.81), the value obtained by the null method was lower in each of the 9 pairs of estimates reported, which suggested a systematic difference (1 in 29 gives P < 0.002).…”

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confidence: 99%

The use of 4‐diphenylacetoxy‐N‐(2‐chloroethyl)‐piperidine (4‐DAMP mustard) for estimating the apparent affinities of some agonists acting at muscarinic receptors in guinea‐pig ileum

Barlow¹,

McMillen²,

Veale³

1991

British J Pharmacology

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1 4-Diphenylacetoxy-N-(2-chloroethyl)-piperidine (4-DAMP mustard), which is known to block muscarinic M3 receptors in preference to muscarinic M2 receptors, was used to estimate the apparent affinity constants of some agonists acting at muscarinic receptors in guinea-pig ileum. Estimates for carbachol and n-pentyl-trimethyl ammonium iodide were similar to published values obtained in similar conditions: those for n-hexyl-trimethyl ammonium iodide were slightly lower. 2 The results for the agonists, n-pentyl-and n-hexyl-trimethyl ammonium iodides and for the partial agonist, n-heptyl-trimethyl ammonium iodide were not as regular as was suggested by Stephenson, though there is an overall increase in apparent affinity with chain length. 3 Estimates of apparent affinity may be affected by hexamethonium, usually present in experiments on ileum. Its absence had little effect on the results with carbachol but reduced the estimates obtained with n-pentyl trimethyl ammonium, which has strong nicotinic effects compared with its muscarinic effects. On ileum treated with tetrodotoxin the values for n-pentyl trimethyl ammonium were similar to those obtained in the presence of hexamethonium (0.28mM): slightly higher estimates of affinity were obtained in the presence of indomethacin (2.8 pM). The nicotinic effects of n-pentyl ammonium may involve the release of prostaglandins. 4 The estimates of apparent affinity did not depend on the method used to calculate them as the 'null' method and the 'operational' method give similar answers. Estimates of the transducer-ratio for the partial agonist, n-heptyl-trimethyl ammonium iodide, were numerically the same as those of its efficacy. 5 This work illustrates the use of 4-DAMP mustard as a tool for measuring the apparent affinity of agonists acting at muscarinic M3 receptors.

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The Gαs‐protein‐mediated pathway may be steadily stimulated by prostanoid EP2 receptors, but not by EP4 receptors

et al. 2022

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EP2 and EP4 prostanoid receptors have long been considered to have similar roles, since they are known to couple with Gαs‐protein and activate cAMP‐mediated signaling pathways. In this study, we re‐evaluated the results of cAMP assays with or without phosphodiesterase (PDE) inhibitor pretreatment. Here, we show that in the absence of PDE inhibitor pretreatment, prostaglandin E2 causes accumulation of cAMP in EP2 receptors, whereas markedly low levels of cAMP accumulated in EP4 receptors. By applying the Black/Leff operational model calculation, we found that EP2 receptors have a biased ability to intrinsically activate the Gαs‐protein‐mediated pathway, whereas EP4 receptors have strong biased activity for the Gαi‐protein‐mediated pathway. Thus, EP2 and EP4 receptors may not be similar Gαs‐coupled receptors but instead substantially different receptors with distinct roles.

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An operational model of pharmacological agonism: the effect of E/[A] curve shape on agonist dissociation constant estimation

Cited by 277 publications

References 14 publications

Estimation of competitive antagonist affinity from functional inhibition curves using the Gaddum, Schild and Cheng‐Prusoíf equations

Estimation of competitive antagonist affinity from functional inhibition curves using the Gaddum, Schild and Cheng‐Prusoíf equations

The use of 4‐diphenylacetoxy‐N‐(2‐chloroethyl)‐piperidine (4‐DAMP mustard) for estimating the apparent affinities of some agonists acting at muscarinic receptors in guinea‐pig ileum

The Gαs‐protein‐mediated pathway may be steadily stimulated by prostanoid EP2 receptors, but not by EP4 receptors

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