Kinetic studies of co-operativity at atrial muscarinic M2 receptors with an 'infinite dilution' procedure

Arthur Christopoulos, Alfred Lanzafame, Albrecht Ziegler, Fred Mitchelson

Research output: Contribution to journalArticleResearchpeer-review

Abstract

The effects of two competitive antagonists and two allosteric ligands on the rate of dissociation of [3H]N-methylscopolamine ([3H]NMS) were studied at atrial muscarinic acetylcholine M2 receptors by the technique of 'infinite dilution.' The dissociation rate for [3H]NMS, initiated by diluting the incubation mixture in a 100-fold volume of buffer, was 0.61 ± 0.10 min-1. Addition of the competitive antagonists, atropine or NMS, to the dilution medium did not alter the observed [3H]NMS dissociation rate. In contrast, gallamine and the bisquaternary, heptane-1,7-bis-(dimethyl-3'-phthalimidopropyl-ammonium bromide) (C7/3'-phth), produced a concentration-dependent slowing of the dissociation rate of [3H]NMS, with IC50 values of 7.5 μM and 196 nM, respectively. Gallamine exhibited an increased modulatory potency when equilibration with the tissue was allowed prior to dilution. The findings showed that the influence of low concentrations of allosteric modulators on the [3H]NMS dissociation rate may be demonstrated separately from any effects on association rate, and that the contact time with the allosteric ligand may influence the extent of these effects.

Original languageEnglish
Pages (from-to)795-800
Number of pages6
JournalBiochemical Pharmacology
Volume53
Issue number6
DOIs
Publication statusPublished - 21 Mar 1997
Externally publishedYes

Keywords

  • allosteric interaction
  • bisquaternary antagonist
  • co-operativity
  • dissociation kinetics
  • gallamine
  • muscarinic acetylcholine M receptors

Cite this

Christopoulos, Arthur ; Lanzafame, Alfred ; Ziegler, Albrecht ; Mitchelson, Fred. / Kinetic studies of co-operativity at atrial muscarinic M2 receptors with an 'infinite dilution' procedure. In: Biochemical Pharmacology. 1997 ; Vol. 53, No. 6. pp. 795-800.
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abstract = "The effects of two competitive antagonists and two allosteric ligands on the rate of dissociation of [3H]N-methylscopolamine ([3H]NMS) were studied at atrial muscarinic acetylcholine M2 receptors by the technique of 'infinite dilution.' The dissociation rate for [3H]NMS, initiated by diluting the incubation mixture in a 100-fold volume of buffer, was 0.61 ± 0.10 min-1. Addition of the competitive antagonists, atropine or NMS, to the dilution medium did not alter the observed [3H]NMS dissociation rate. In contrast, gallamine and the bisquaternary, heptane-1,7-bis-(dimethyl-3'-phthalimidopropyl-ammonium bromide) (C7/3'-phth), produced a concentration-dependent slowing of the dissociation rate of [3H]NMS, with IC50 values of 7.5 μM and 196 nM, respectively. Gallamine exhibited an increased modulatory potency when equilibration with the tissue was allowed prior to dilution. The findings showed that the influence of low concentrations of allosteric modulators on the [3H]NMS dissociation rate may be demonstrated separately from any effects on association rate, and that the contact time with the allosteric ligand may influence the extent of these effects.",
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Kinetic studies of co-operativity at atrial muscarinic M2 receptors with an 'infinite dilution' procedure. / Christopoulos, Arthur; Lanzafame, Alfred; Ziegler, Albrecht; Mitchelson, Fred.

In: Biochemical Pharmacology, Vol. 53, No. 6, 21.03.1997, p. 795-800.

Research output: Contribution to journalArticleResearchpeer-review

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T1 - Kinetic studies of co-operativity at atrial muscarinic M2 receptors with an 'infinite dilution' procedure

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