Neuronal nicotinic alpha 7 receptor expressed in Xenopus oocytes presents five putative binding sites for methyllycaconitine

J Physiol. 1996 Feb 15;491 ( Pt 1)(Pt 1):151-61. doi: 10.1113/jphysiol.1996.sp021203.


1. The recently isolated compound methyllycaconitine (MLA) is a plant toxin which is a competitive inhibitor of nicotinic acetylcholine receptors (nAChRs). We found that homomeric alpha 7 receptors display a very high sensitivity to MLA with an IC50 in the picomolar range. 2. The competitive nature of the alpha 7 MLA blockade was reinforced by the observation that this compound has no action on wild-type serotoninergic receptors (5-HT3), whereas it is a powerful antagonist of chimaeric receptors alpha 7-5-HT3. 3. The time course of MLA inhibition of the wild-type (WT) alpha 7 follows a monotonic exponential decay whose time constant is proportional to the MLA concentration and could be described by a bimolecular mechanism with a forward rate constant (k+) of 2.7 x 10(7) S-1 M-1. In contrast, recovery from MLA inhibition displays an S-shaped time course that is incompatible with a simple bimolecular reaction. 4. Given the pentameric nature of the neuronal nicotinic receptors, a linear chain model, including five putative MLA binding sites corresponding to the homomeric nature of alpha 7, is proposed. 5. Both onset and recovery data obtained on the alpha 7 wild-type receptor are adequately described by this model assuming that a single MLA molecule is sufficient to block receptor function. 6. Analysis of MLA blockade and recovery of reconstituted heteromeric alpha 4 beta 2 receptors reveals, as expected, a time course compatible with only two binding sites for the toxin and, thus, further supports the validity of our model.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Aconitine / analogs & derivatives*
  • Aconitine / metabolism
  • Aconitine / pharmacology
  • Animals
  • Binding Sites / drug effects
  • Female
  • Ion Channel Gating / drug effects
  • Ion Channel Gating / physiology
  • Kinetics
  • Neurons / metabolism*
  • Nicotinic Antagonists / metabolism*
  • Nicotinic Antagonists / pharmacology
  • Oocytes / metabolism
  • Receptors, Nicotinic / biosynthesis
  • Receptors, Nicotinic / metabolism*
  • Xenopus laevis


  • Nicotinic Antagonists
  • Receptors, Nicotinic
  • methyllycaconitine
  • Aconitine