Tetramethylammonium ions alter sodium-channel gating in Myxicola.
In Myxicola axons, substitution of tetramethylammonium (TMA+) for Cs+ alters intramembrane charge movements (gating currents). Although the total charge moved during and following a depolarizing step remains constant, with TMA+ the ON response has additional slower component(s), and the OFF response is retarded. Concommitantly, TMA+ produces the same voltage-dependent block of Na+ inactivation in Myxicola as has been observed in other preparations. At large positive potentials as many as 70% of the Na+ channels fail to inactivate in the steady state. In addition, TMA+ slows Na+ activation, retards the inactivation of those Na+ channels that remain able to inactivate, and decreases the maximum Na+ conductance. The steady-state Na+ conductance induced by internal TMA+ or Na+ is consistent with a scheme in which these internal cations simply modify Na+ channels in an all-or-none fashion so that a fraction become incapable of inactivating.
D000818:Animals; D001369:Axons / Q000502:physiology*; D007473:Ion Channels / Q000187:drug effects / Q000502:physiology*; D008564:Membrane Potentials / Q000187:drug effects; D011077:Polychaeta; D000644:Quaternary Ammonium Compounds / Q000494:pharmacology*; D012964:Sodium / Q000378:metabolism*
D007473:Ion Channels; D000644:Quaternary Ammonium Compounds; D012964:Sodium; C027917:tetramethylammonium