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The Journal of Experimental Biology 205, 869-876 (2002)
© 2002 The Company of Biologists Limited

Cn11, the first example of a scorpion toxin that is a true blocker of Na+ currents in crayfish neurons

Martha E. Ramirez-Dominguez1, Timoteo Olamendi-Portugal1, Ubaldo Garcia2, Consuelo Garcia1, Hugo Arechiga3 and Lourival D. Possani1,*

1 Department of Molecular Recognition and Structural Biology, Biotechnology Institute, Universidad Nacional Autónoma de México, Avenida Universidad 2001, Cuernavaca 62210, México,
2 Department of Physiology, Biophysics and Neurosciences, Centro de Investigación y de Estudios Avanzados del I.P.N. México DF 07000 and
3 Division of Graduate Studies and Research, Medical School, Universidad Nacional Autónoma de México, Ciudad Universitaria, México DF 04510

*Author for correspondence (e-mail: possani{at}ibt.unam.mx)

Accepted 4 January 2002

A novel crustacean toxin (Cn11) was isolated and characterized from the venom of the Mexican scorpion Centruroides noxius Hoffmann. It contains 63 amino acid residues and is stabilized by four disulphide bridges. It is lethal to crustaceans (Cambarellus montezumae), less toxic to insects (crickets) and non-toxic to mammals (mice) at the doses assayed. In neurons isolated from the X organ–sinus gland system of the crayfish Procambarus clarkii, it blocks the Na+ currents with an estimated Km of 320 nmol l–1, without affecting the Ca2+ and K+ currents. The voltage-gated tetrodotoxin-sensitive Na+ current was recorded from X organ neurons in culture 24 h after plating using the whole-cell clamp configuration. The Na+ current was isolated by blocking Ca2+ currents with Cd2+ and Cs+ and K+ currents with tetraethylammonium and 4-aminopyridine. Under control conditions, the Na+ currents were activated at –40 mV with a maximum amplitude at 0 mV. In the presence of 1 µmol l–1 Cn11, the Na+ current amplitude was reduced by 75 % without apparent modifications to the gating mechanism. These findings suggest that Cn11 selectively blocks a Na+ channel. It is the first representative of a new group of scorpion toxins specific for this molecular target.

Key words: amino acid sequence, Centruroides noxius, crayfish, neuron, Na+ channel, Procambarus clarkii, scorpion toxin.


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