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XB-ART-14136
J Physiol 1998 Nov 01;512 ( Pt 3):693-705.
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Mechanistic link between lidocaine block and inactivation probed by outer pore mutations in the rat micro1 skeletal muscle sodium channel.

Kambouris NG , Hastings LA , Stepanovic S , Marban E , Tomaselli GF , Balser JR .


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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.

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References [+] :
Adelman, The effects of external potassium and long duration voltage conditioning on the amplitude of sodium currents in the giant axon of the squid, Loligo pealei. 1969, Pubmed