[Simvastatin].
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Anticholesteremic Agents↗
Biomedical subjects
K Mohr
Publications and source records attributed to K Mohr.
Opposite effects of alcuronium on agonist and on antagonist binding to muscarinic receptors.
Alcuronium is known to retard allosterically the dissociation of [3H]N-methylscopolamine from muscarinic M2 receptors, thereby augmenting the binding of this antagonist. Functionally, alcuronium behaves as a weak antimuscarinic agent and induces in combination with N-methylscopolamine an overadditive antimuscarinic action with oxotremorine-M as the agonist. The effect of alcuronium on the binding of [3H]oxotremorine-M was studied in porcine heart homogenates. Agonist binding was concentration dependently inhibited with a Ki = 0.48 +/- 0.03 microM (means +/- S.D., n = 3). Under identical conditions [3H]N-methylscopolamine binding was elevated. Alcuronium, 100 microM, which nearly prevented the dissociation of [3H]N-methylscopolamine, retarded the rate of dissociation of [3H]oxotremorine-M only by a factor of two. These findings support the notion that the overadditive antimuscarinic action of alcuronium in conjunction with N-methylscopolamine is based on a shift by alcuronium of the interplay between agonist and antagonist in favour of the antagonist.
Alcuronium↗
Two-point kinetic experiments to quantify allosteric effects on radioligand dissociation.
Allosteric modulation of a receptor may be proved experimentally by demonstrating an altered radioligand dissociation in the presence of the allosteric modulator. Two-point kinetic experiments provide a screening-type approach to determine the delay of radioligand dissociation caused by allosteric modulation. In this article, Evi Kostenis and Klaus Mohr describe a pitfall in the data analysis that may lead to a suboptimum determination of the allosteric potency in the case of monophasic dissociations, and suggest how this problem may be resolved.
Allosteric Regulation↗
[Calcium and magnesium salts in leg cramps?].
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Calcium↗
Potentiation by alcuronium of the antimuscarinic effect of N-methylscopolamine in guinea pig left atria.
Alcuronium is known to stabilize allosterically the binding of the muscarinic antagonist N-methylscopolamine to muscarinic M2 receptors and thus to elevate the equilibrium binding of N-methylscopolamine in homogenized cardiac tissue. In order to check for a functional consequence of this effect, the action of alcuronium alone and in combination with N-methylscopolamine was determined in contracting guinea pig left auricles with oxotremorine-M as the negative inotropic agonist. For sake of comparison, the allosteric modulator W84 = hexane-1,6-bis(dimethyl-3'- phthalimidopropyl-ammonium bromide) was included. Alcuronium displayed a weak antimuscarinic action (pA2 = 5.7). In conjunction with 10(-7) M N-methylscopolamine, alcuronium (> or = 10(-6) M) induced a more pronounced antimuscarinic effect than expected for a combination of competitive antagonists. The extent of overadditivity with combinations of W84 and 10(-7) M N-methylscopolamine was smaller. In conclusion, alcuronium potentiates the antimuscarinic effect of N-methylscopolamine in contracting cardiac preparations with high effectivity.
Alcuronium↗
Variation of the oxime function of bispyridinium-type allosteric modulators of M2-cholinoceptors.
The bisbenzylether of the bispyridinium oxime, DUO 3-O (4,4'-Bis-[(2,6-dichlorobenzyloxyimino)-methyl]-1,1'-propane-1,3- diyl-bispyridinium dibromide), has been found to stabilize the antagonist binding to the M2-cholinoceptors which is indicative of an allosteric action. The oxygen of the oxime group was replaced with a nitrogen and a CH2-group leading to DUO 3-N and 3-C, respectively. The allosteric potency of the compounds was characterized by the concentrations which retarded the rate of dissociation of [3H]N-methyl-scopolamine from porcine cardiac cholinoceptors by a factor of 2 (EC50). The hydrazone derivative DUO 3-N was found to be the most active compound (ED50 = 2.7 microM) exceeding in activity DUO 3-O by a factor of 1.6 and DUO 3-C by a factor of 5. No correlation was found between the lipophilicity, determined as octanol/water partition coefficient, and the allosteric potency. The distribution of charges in the molecules was calculated by means of PEOE and displayed as Kohonen maps: The calculations exhibit a shift of the positive charge in the pyridinium ring from the nitrogen to the carbon atom in para-position when going from DUO 3-C to 3-O and 3-N. This shift parallels the rank order of the allosteric potency. From these results the conclusion has been drawn that the between distance the terminal ring-system and the positive charge is pivotal for the interaction of the allosteric modulators with the receptor protein.
Allosteric Regulation↗
[Lactones. 28. EPC-synthesis, structure and pharmacology of "lactonized" and "lactamized" analogues of acetylcholine].
The enantiopure gamma-aminomethyl-gamma-butyrolactones (S)- and (R)-4a-d represent constrained analogues of acetylcholine, which were synthesized from D- or L-glutamic acid following two different routes. In addition, the corresponding lactames (S)- and (R)-10 were prepared by enantioselective synthesis. Only moderate activity was found at acetylcholine sites at the guinea pig atrium.
Acetylcholine↗
[Therapeutic drugs. Magnesium].
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Absorption↗
Search for the pharmacophore of bispyridinium-type allosteric modulators of muscarinic receptors.
The bis(dichlorobenzyl) ether of the bispyridinium oxime TMB 4 stabilizes antagonist binding to M2-cholinoceptors which is indicative of an allosteric action. More than 10 derivatives of the lead compound were synthesized to investigate structure-activity relationships. The allosteric potency of the compounds was indicated by the concentrations which retarded the rate of dissociation of [3H]N-methylscopolamine from porcine cardiac cholinoceptors by a factor of 2 (EC50). Compared with TMB 4, the bis(dichlorobenzyl) derivative 4a displayed a more than 200-fold higher potency (EC50 = 4.7 microM). One of the dichlorobenzyl groups could be replaced by a methyl group without loss of activity (EC50 = 4.5 microM). Further shortening of this end of the molecule was accompanied by a moderate decline in potency to a minimum of EC50 = 26 microM. The second quaternary nitrogen was not a prerequisite for an allosteric activity. It is concluded that one half of the lead compound is pivotal for an interaction with the allosteric site of the M2-cholinoceptor, whereas the opposite end of the molecule modulates the allosteric activity.
Allosteric Regulation↗
Allosteric effects of the alkane-bis-ammonium compound W84 and of tacrine on [3H]pirenzepine binding at M1-receptors in rat cerebral cortex.
The bis-quaternary W84, hexamethylene-bis-[dimethyl-(3-phthalimidopropyl)-ammonium bromide], is a potent allosteric modulator of M2-cholinoceptors. In this study we aimed at quantifying its allosteric effect on the dissociation of [3H]pirenzepine from M1-cholinoceptors in rat cerebral cortex and to measure the effects on association and equilibrium binding of [3H]pirenzepine. For sake of comparison tacrine was included which is known to be a potent allosteric modulator of [3H]pirenzepine binding to M1-receptors. Under control conditions (3 mM MgHPO4, 50 mM Tris-HCl, pH 7.4, 23 degrees) [3H]pirenzepine binding was characterized by KD = 5 nM and Bmax = 965 fmol/mg membrane protein, the rate constants amounting to k+1 = 5.0 microM-1 x min-1 and k-1 = 0.031 min-1. W84 and tacrine reduced [3H]pirenzepine binding concentration-dependently with IC50-values of 1.9 microM and 2.6 microM, respectively. [3H]pirenzepine association was inhibited by the compounds with EC50,ass = 1.8 microM for W84 and EC50,ass = 2.4 microM for tacrine. The concentrations reducing the dissociation rate by 50% amounted to EC50,diss = 21 microM for W84 and to EC50,diss = 54 microM for tacrine. Compared with W84, the dose-reponse curves of tacrine for the investigated effects were significantly steeper. In conclusion, WS84 affected [3H]pirenzepine binding to M1-receptors allosterically with a higher potency than tacrine but probably by a different mechanism.
Allosteric Regulation↗
A stable and highly potent hexamethonium derivative which modulates muscarinic receptors allosterically in guinea-pig hearts.
W84 (N,N,N',N'-tetramethyl-N,N'-bis-(3-phthalimidopropyl)-N,N'-hexane- 1,6- diyl-bis-ammonium dibromide) is a potent stabilizer of antagonist binding to muscarinic receptors; however, W84 hydrolyses in aqueous buffered medium. The synthesis of the stable derivative CHIN3/6 is presented containing a 2-phenyl-quinazolinone instead of the labile phthalimide substituent. This compound retarded [3H]N-methylscopolamine-dissociation in guinea-pig cardiac membranes with slightly higher potency than W84, the EC50 values amounting to 7.5 x 10(-7) and 13 x 10(-7) M, respectively. Molecular modelling revealed differences in the electron density of the substituents and in their molecular shape. It is suggested that the derivatives use partially different sites of attachment when occupying the allosteric binding site of the receptor protein.
Allosteric Regulation↗