[Abscence of the tetrodotoxin effect on sodium permeability under conditions of prolonged depolarization]

Using frog muscle fibres, it is shown that 10(-6) tetrodotoxin does not practically affect the membrane permeability to lithium ions during a continious depolarization, with the membrane potential being near zero, but causes half a decreased lithium permeability under conditions of normal membrane potential. The absolute value of the lithium permeability for these two states are very close. A 10 mM tetraethylammonium chloride does not influence the lithium permeability of muscle membrane with the normal membrane potential and during a continious depolarization. It is proposed that intact and inactivated sodium channals may have almost equal ion passing capacities, but differ in their gate systems, especially as concerns its interaction with tetrodotoxin.