Monoclonal immunotoxin acting on the Na+ channel, with properties similar to those of a scorpion toxin

The authors describe the properties of a monoclonal antibody against the Na+ channel. The antibody, 72.38, competitively inhibited the binding of an 125I-labeled toxin from the Brazilian scorpion Tityus serrulatus (125I-TiTXγ) to Na+ channels of rat brain membranes. The inhibition of 125I-TiTXγ binding also was observed with the solubilized Na+ channel from rat brain membranes. Antibody 72.38 antagonized 125I-TiTXγ binding to Na+ channels from different animal species (fish, avian, and mammalian) and from different tissues (electroplax, brain, heart, and muscle). Moreover, 72.38 has been used for immunofluorescence labeling of Na+ channels in rat sciatic nodes of Ranvier and cultured dorsal root ganglion cells. Electrophysiological experiments on rat muscle cells fully confirmed the similarity between TiTXγ and 72.38 seen in binding experiments. TiTXγ and 72.38 are without effect on the ion selectivity of the Na+ channel, but they both drastically change the voltage-dependence of activation and inactivation of the Na+ channel