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 language | English |
|---|---|
| Pages (from-to) | 795-800 |
| Number of pages | 6 |
| Journal | Biochemical Pharmacology |
| Volume | 53 |
| Issue number | 6 |
| DOIs | |
| Publication status | Published - 21 Mar 1997 |
| Externally published | Yes |
Keywords
- allosteric interaction
- bisquaternary antagonist
- co-operativity
- dissociation kinetics
- gallamine
- muscarinic acetylcholine M receptors
Cite this
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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 journal › Article › Research › peer-review
TY - JOUR
T1 - Kinetic studies of co-operativity at atrial muscarinic M2 receptors with an 'infinite dilution' procedure
AU - Christopoulos, Arthur
AU - Lanzafame, Alfred
AU - Ziegler, Albrecht
AU - Mitchelson, Fred
PY - 1997/3/21
Y1 - 1997/3/21
N2 - 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.
AB - 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.
KW - allosteric interaction
KW - bisquaternary antagonist
KW - co-operativity
KW - dissociation kinetics
KW - gallamine
KW - muscarinic acetylcholine M receptors
UR - http://www.scopus.com/inward/record.url?scp=0030944020&partnerID=8YFLogxK
U2 - 10.1016/S0006-2952(96)00814-3
DO - 10.1016/S0006-2952(96)00814-3
M3 - Article
VL - 53
SP - 795
EP - 800
JO - Biochemical Pharmacology
JF - Biochemical Pharmacology
SN - 0006-2952
IS - 6
ER -