Localization of the voltage-dependent sodium channel in the electric eel electrocyte using biotin-labeled scorpion toxin

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A scorpion toxin conjugated with biotin and avidin has been used to investigate the location of the voltage-dependent Na-channel in the electric organ of Electrophorus electricus. Distribution of the conjugated scorpion toxin was visualized under a light or an electron microscope by using biotinylated peroxidase and diaminobenzidine. A dense staining was observed on the innervated surface of the electroplax plasmalemma, but not on the non-innervated surface. Electron micrographs at a higher magnification showed that the caveolar invaginations of the innervated membrane surface were also stained. This specific staining was completely blocked by an excess amount of unmodified scorpion toxin or by a high concentration of KCl in the incubation medium.