External pore residue mediates slow inactivation in mu 1 rat skeletal muscle sodium channels.

摘要: 1. Upon depolarization, voltage-gated sodium channels assume non-conducting inactivated states which may be characterized as "fast' or "slow' depending on the length of repolarization period needed for recovery. Skeletal muscle Na+ channel alpha-subunits expressed in Xenopus laevis oocytes display anomalous gating behaviour, with substantial slow inactivation after brief depolarizations. We exploited this kinetic behaviour to examine structural basis inactivation. 2. While fast is mediated by cytoplasmic occlusion pore III-IV linker residues, features are unknown. Since external pore-lining residues modulate C-type potassium channels, we performed serial cysteine mutagenesis permeation loop (P-loop) rat skeletal (mu 1) determine whether similarly placed involved 3. Wild-type and mutant were heterologously oocytes, currents recorded using a two-electrode voltage clamp. Slow depolarizations was eliminated W402C mutation domain I. Cysteine substitution homologous tryptophan domains II, III IV did not alter 4. Analogous mutation, coexpression wild-type alpha-subunit brain beta 1-subunit attenuated However, imposed delay recovery from inactivation, while not. propose that through distinct mechanisms. 5. Removal I1303Q; F1304Q; M1305Q markedly slowed development involves conformational changes pore. Mutations affect appear interact despite their remote positions channel.