Publisher Summary This chapter discusses the batrachotoxin A ‘ 3 H’ benzoate binding to sodium channels. Voltage-dependent Na + channels are responsible for a selective increase in Na + permeability that underlies the generation of action potentials in excitable membranes of nerve and muscle. The major subunit of the Na + channel is a large glycoprotein—smaller β-subunits are associated with Na + channels of brain. An initial threshold depolarization of nerve and muscle activates the voltage-dependent Na + channel and induces a series of conformational changes, leading to a transient open or conducting state. This is followed by a voltage-dependent conversion to an inactive non-conductive state, from which the channel then returns to the resting state. There are several different subtypes of Na + channels, but all are likely to be similar in structure and functional attributes. The chapter discusses the primary structures of Na + channels from eel and rat, and models are proposed in which four homologous units, each with six transmembrane sections, are organized to form a central pore.