The Journal of Membrane Biology

, Volume 48, Issue 4, pp 357–364 | Cite as

Binding of radioactively labeled saxitoxin to the squid giant axon

  • G. R. Strichartz
  • R. B. Rogart
  • J. M. Ritchie


The binding of saxitoxin, a specific inhibitor of the sodium conductance in excitable membranes, has been measured in giant axons from the squid,Loligo pealei. Binding was studied by labeling saxitoxin with tritium, using a solvent-exchange technique, and measuring the toxin uptake by liquid scintillation counting. Total toxin binding is the sum of a saturable, hyperbolic binding component, with a dissociation constant at 2–4°C of 4.3±1.7nm (meanse), and a linear, nonsaturable component. The density of saturable binding sites is 166±20.4 μm−2. From this density and published values of the maximum sodium conductance, the conductance per toxin site is estimated to be about 7 pS, assuming sequential activation and inactivation processes (F. Bezanilla & C.M. Armstrong, 1977,J. Gen. Physiol.70: 549). This single site conductance value of 7 pS is in close agreement with estimates of the conductance of one open sodium channel from measurements of gating currents and of noise on squid giant axons, and is consistent with the hypothesis that one saxitoxin molecule binds to one sodium channel.


Tritium Sodium Channel Giant Axon Saxitoxin Binding Component 
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Copyright information

© Springer-Verlag New York Inc 1979

Authors and Affiliations

  • G. R. Strichartz
    • 1
    • 2
    • 3
  • R. B. Rogart
    • 1
    • 2
    • 3
  • J. M. Ritchie
    • 1
    • 2
    • 3
  1. 1.Department of Physiology and BiophysicsState University of New YorkStony Brook
  2. 2.Department of PharmacologyYale University, School of MedicineNew Haven
  3. 3.Marine Biological LaboratoryWoods Hole

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