Allosteric effects of the alkane-bis-ammonium compound W84 and of tacrine on [3H]pirenzepine binding at M1-receptors in rat cerebral cortex

Pharmacol Toxicol. 1994 Dec;75(6):391-4. doi: 10.1111/j.1600-0773.1994.tb00380.x.


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.

MeSH terms

  • Allosteric Regulation
  • Animals
  • Binding, Competitive / drug effects
  • Cerebral Cortex / drug effects*
  • Cerebral Cortex / metabolism
  • Cholinesterase Inhibitors / toxicity*
  • Dose-Response Relationship, Drug
  • Isoindoles
  • Male
  • Phthalimides / toxicity*
  • Pirenzepine / metabolism*
  • Rats
  • Rats, Sprague-Dawley
  • Receptors, Cholinergic / drug effects*
  • Receptors, Cholinergic / metabolism
  • Structure-Activity Relationship
  • Tacrine / toxicity*


  • Cholinesterase Inhibitors
  • Isoindoles
  • Phthalimides
  • Receptors, Cholinergic
  • hexamethylenebis(dimethyl-(3-phthalimidopropyl)ammonium bromide)
  • Pirenzepine
  • Tacrine