Mechanistic link between lidocaine block and inactivation probed by outer pore mutations in the rat micro1 skeletal muscle sodium channel.
1. Mutations that disrupt Na+ channel fast inactivation attenuate lidocaine (lignocaine)-induced use dependence; however, the pharmacological role of slower inactivation processes remains unclear. In Xenopus oocytes, tryptophan substitution in the outer pore of the rat skeletal muscle channel (micro1-W402) alters partitioning among fast- and slow-inactivated states. We therefore examined the effects of W402 mutations on lidocaine block. 2. Recovery from inactivation exhibited three kinetic components (IF, fast; IM, intermediate; IS, slow). The effects of W402A and W402S on IF and IS differed, but both mutants (with or without beta1 subunit coexpression) decreased the amplitude of IM. In wild-type channels, lidocaine imposed a delayed recovery component with intermediate kinetics, and use-dependent block was attenuated in both W402A and W402S. 3. To examine the pharmacological role of IS relative to IM, drug-exposed beta1-coexpressed channels were subjected to 2 min depolarizations. Lidocaine had no effect on sodium current (INa) after a 1 s hyperpolarization interval that allowed recovery from IM but not IS, suggesting that lidocaine affinity for IS is low. 4. Both W402 mutations reduced occupancy of IM in drug-free conditions, and also induced resistance to use-dependent block. We propose that lidocaine-induced use dependence may involve an allosteric conformational change in the outer pore.
Kambouris
N G
NG
Division of Cardiac Anesthesiology, Department of Anesthesia and Critical Care Medicine, Department of Medicine, The Johns Hopkins University School of Medicine, Baltimore, MD, USA.
Hastings
L A
LA
Stepanovic
S
S
Marban
E
E
Tomaselli
G F
GF
Balser
J R
JR
D000818:Animals; D004558:Electric Stimulation; D004594:Electrophysiology; D007700:Kinetics; D008012:Lidocaine / Q000494:pharmacology*; D008564:Membrane Potentials / Q000502:physiology; D018482:Muscle, Skeletal / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D016297:Mutagenesis, Site-Directed; D009154:Mutation / Q000502:physiology*; D009865:Oocytes / Q000378:metabolism; D018408:Patch-Clamp Techniques; D051381:Rats; D026941:Sodium Channel Blockers; D015222:Sodium Channels / Q000235:genetics* / Q000378:metabolism*; D014982:Xenopus laevis
D026941:Sodium Channel Blockers; D015222:Sodium Channels; D008012:Lidocaine