1.Electromyographic assessment of the neuromuscular blockade produced in vivo by anatoxin-a in the rat.
Valentine WM1, Schaeffer DJ, Beasley VR. Toxicon. 1991;29(3):347-57.
The indirectly evoked compound action potentials (ECAP) of the plantar muscles of the rat were used to investigate the pharmacodynamics in vivo of the neuromuscular blockade produced by anatoxin-a. Onset time to maximum depression and the magnitude of maximum depression in amplitude of the ECAP were dose-dependent. The mean maximum percent depression (+/- S.D.) of the ECAP induced by single, supramaximal stimulations of the posterior tibial nerve after i.v. doses of (+)anatoxin-a hydrochloride at 0, 50, 100, 200 and 800 micrograms/kg were 3 (4), 53 (15), 82 (7), 95 (2), and 100 (1), respectively. The ED50 (95% confidence limits) for depression of the ECAP was 47 mg/kg (39-57 micrograms/kg). Rats administered 200 micrograms/kg or less of (+)anatoxin-a hydrochloride had 75% return of the pretoxin amplitude of the ECAP within 93 min. Animals dosed at 800 micrograms/kg did not have return of neuromuscular function and died despite mechanical ventilation, suggesting a lethal mechanism(s) of action in addition to respiratory paralysis.
2.Synthetic and conformational studies on anatoxin-a: a potent acetylcholine agonist.
Koskinen AM, Rapoport H. J Med Chem. 1985 Sep;28(9):1301-9.
Anatoxin-a is a powerful nicotinic acetylcholine receptor agonist. Its recently reported synthesis has been further optimized to provide anatoxin-a of greater than 99% optical purity in 10% overall yield. The geometry of solid anatoxin-a has been determined by X-ray crystallography of its hydrochloride. The solution conformation has been determined by 500-MHz 1H NMR spectroscopy, utilizing 2D NMR methods and homonuclear decouplings. For further comparisons, force field calculations have been employed to evaluate the differences in energy between the various conformations available for anatoxin-a. The molecule is seen to adopt the same ring conformation both in solution and in the crystal. Comparison of this conformation with the models proposed for acetylcholine receptor activation shows good agreement and allows for further inferences concerning the stereodiscrimination by the receptor.