Lidocaine induces a slow inactivated state in rat skeletal muscle sodium channels.
1. Local anaesthetics such as lidocaine (lignocaine) interact with sodium channels in a manner that is exquisitely sensitive to the voltage-dependent conformational state of the ion channel. When depolarized in the presence of lidocaine, sodium channels assume a long-lived quiescent state. Although studies over the last decade have localized the lidocaine receptor to the inner aspect of the aqueous pore, the mechanistic basis of depolarization-induced 'use-dependent' lidocaine block remains uncertain. 2. Recent studies have shown that lowering the extracellular Na+ concentration ([Na+]o) and mutations in the sodium channel outer P-loop modulate occupancy of a quiescent 'slow' inactivated state with intermediate kinetics (termed IM) that involves structural rearrangements in the outer pore. 3. Site-directed mutagenesis and ion-replacement experiments were performed using voltage-clamped Xenopus oocytes and cultured (HEK-293) cells expressing wild-type and mutant rat skeletal muscle (mu1) sodium channels. 4. Our results show that lowering [Na+]o potentiates use-dependent lidocaine block. The effect of [Na+]o is maintained despite a III-IV linker mutation that partially disrupts fast inactivation (F1304Q). In contrast, the effect of lowering [Na+]o on lidocaine block is reduced by a P-loop mutation (W402A) that limits occupancy of IM. 5. Our findings are consistent with a simple allosteric model where lidocaine binding induces channels to occupy a native slow inactivated state that is inhibited by [Na+]o.
Chen
Z
Z
Departments of Anesthesiology and Pharmacology, Vanderbilt University School of Medicine, Nashville, TN 37232, USA.
Ong
B H
BH
Kambouris
N G
NG
Marbán
E
E
Tomaselli
G F
GF
Balser
J R
JR
D019943:Amino Acid Substitution; D000818:Animals; D002460:Cell Line; D005260:Female; D006801:Humans; D007700:Kinetics; D008012:Lidocaine / Q000494:pharmacology*; D008564:Membrane Potentials / Q000187:drug effects; D018482:Muscle, Skeletal / Q000502:physiology*; D016297:Mutagenesis, Site-Directed; D009865:Oocytes; D011487:Protein Conformation / Q000187:drug effects; D017433:Protein Structure, Secondary; D051381:Rats; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D012964:Sodium / Q000494:pharmacology; D015222:Sodium Channels / Q000737:chemistry / Q000187:drug effects / Q000502:physiology*; D014162:Transfection; D014982:Xenopus laevis
D011994:Recombinant Proteins; D015222:Sodium Channels; D008012:Lidocaine; D012964:Sodium