Toxin and kinetic profile of rat brain type III sodium channels expressed in Xenopus oocytes

Sodium (Na +) channels are members of a multigene family and are responsible for generation and propagation of the action potential in excitable cells. We have assembled, in a transcription-competent vector, a full-length cDNA clone encoding the rat brain type III Na + channel. Xenopus oocytes microinjected with in vitro synthesized mRNA expressed functional rat brain Na + channels from such ‘cloned’ RNA transcripts. We found that type III Na + currents in whole cell microelectrode voltage clamp and in cell-attached patch recordings decayed much more slowly than any other reported Na + current. In addition, we saw typical and additive effects of α-and β-scorpion toxins, suggesting that the Na + channel α-subunit itself contains functional and distinct toxin binding sites.