The selectivity filter of the voltage-gated sodium channel is involved in channel activation.
Amino acids located in the outer vestibule of the voltage-gated Na+ channel determine the permeation properties of the channel. Recently, residues lining the outer pore have also been implicated in channel gating. The domain (D) IV P-loop residue alanine 1529 forms a part of the putative selectivity filter of the adult rat skeletal muscle (mu1) Na+ channel. Here we report that replacement of alanine 1529 by aspartic acid enhances entry to an ultra-slow inactivated state. Ultra-slow inactivation is characterized by recovery time constants on the order of approximately 100 s from prolonged depolarizations and by the fact that entry to this state can be reduced by binding to the pore of a mutant mu-conotoxin GIIIA, suggesting that ultra-slow inactivation may reflect a structural rearrangement of the outer vestibule. The voltage dependence of ultra-slow inactivation in DIV-A1529D is U-shaped, with a local maximum near -60 mV, whereas activation is maximal only above -20 mV. Furthermore, a train of brief depolarizations produces more ultra-slow inactivation than a single maintained depolarization of the same duration. These data suggest that ultra-slow inactivation emanates from "partially activated" closed states and that the P-loop in DIV may undergo a conformational change during channel activation, which is accentuated by DIV-A1529D.
Hilber
K
K
Institute of Pharmacology, University of Vienna, 1090 Vienna, Austria.
Sandtner
W
W
Kudlacek
O
O
Glaaser
I W
IW
Weisz
E
E
Kyle
J W
JW
French
R J
RJ
Fozzard
H A
HA
Dudley
S C
SC
Todt
H
H
D020413:3' Untranslated Regions; D020121:5' Untranslated Regions; D000818:Animals; D001921:Brain / Q000378:metabolism; D020916:Conotoxins / Q000378:metabolism; D004594:Electrophysiology; D020128:Inhibitory Concentration 50; D007700:Kinetics; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D018408:Patch-Clamp Techniques; D017354:Point Mutation; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D051381:Rats; D015222:Sodium Channels / Q000737:chemistry* / Q000235:genetics* / Q000378:metabolism; D013997:Time Factors; D014981:Xenopus
D020413:3' Untranslated Regions; D020121:5' Untranslated Regions; D020916:Conotoxins; D015222:Sodium Channels; C046101:conotoxin GIII