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Related Experiment Videos

Grayanotoxin opens Na channels from inside the squid axonal membrane.

I Seyama1, K Yamada, R Kato

  • 1Department of Physiology, School of Medicine, Hiroshima University, Japan.

Biophysical Journal
|February 1, 1988
PubMed
Summary

Grayanotoxin II (GTX II) causes squid axon depolarization, but its receptor is internal. GTX II permeates the cell membrane via lipid diffusion, not channels or carriers.

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Area of Science:

  • Neuroscience
  • Molecular Biology
  • Pharmacology

Background:

  • Grayanotoxins (GTXs) are diterpenoid compounds known to affect ion channels.
  • The precise mechanism and site of action of GTXs on neuronal membranes remain incompletely understood.

Purpose of the Study:

  • To investigate the mechanism of action and receptor localization of alpha-dihydro-grayanotoxin II (alpha-H2-GTX II) on squid giant axons.
  • To determine whether GTX II acts on the external or internal surface of the neuronal membrane.

Main Methods:

  • External application of alpha-H2-GTX II to nonperfused squid giant axons.
  • Intracellular perfusion of squid giant axons to assess the effect of internal GTX II application.
  • Use of tritium-labeled alpha-H2-GTX II ([3H]alpha-H2-GTX II) to study membrane permeation.

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Main Results:

  • External application of alpha-H2-GTX II induced significant membrane depolarization.
  • Intracellular perfusion markedly reduced the depolarization effect, indicating an internal site of action.
  • [3H]alpha-H2-GTX II permeated the cell membrane, but not through Na channels or carrier systems.
  • Hydrophilic grayanotoxin analogues were only effective when applied internally, supporting an intracellular receptor.

Conclusions:

  • The receptor for alpha-dihydro-grayanotoxin II is located on the internal surface of the neuronal membrane.
  • GTX II permeates the squid giant axon membrane through passive diffusion across the lipid bilayer.
  • These findings elucidate the transport and action mechanism of grayanotoxins in neurons.