Transient impairment of the axolemma following regional anaesthesia by lidocaine in humans.
The local anaesthetic lidocaine is known to block voltage-gated Na(+) channels (VGSCs), although at high concentration it was also reported to block other ion channel currents as well as to alter lipid membranes. The aim of this study was to investigate whether the clinical regional anaesthetic action of lidocaine could be accounted for solely by the block of VGSCs or whether other mechanisms are also relevant. We tested the recovery of motor axon conduction and multiple measures of excitability by 'threshold-tracking' after ultrasound-guided distal median nerve regional anaesthesia in 13 healthy volunteers. Lidocaine caused rapid complete motor axon conduction block localized at the wrist. Within 3 h, the force of the abductor pollicis brevis muscle and median motor nerve conduction studies returned to normal. In contrast, the excitability of the motor axons at the wrist remained markedly impaired as indicated by a 7-fold shift of the stimulus-response curves to higher currents with partial recovery by 6 h and full recovery by 24 h. The strength-duration properties were abnormal with markedly increased rheobase and reduced strength-duration time constant. The changes in threshold during electrotonus, especially during depolarization, were markedly reduced. The recovery cycle showed increased refractoriness and reduced superexcitability. The excitability changes were only partly similar to those previously observed after poisoning with the VGSC blocker tetrodotoxin. Assuming an unaltered ion-channel gating, modelling indicated that, apart from up to a 4-fold reduction in the number of functioning VGSCs, lidocaine also caused a decrease of passive membrane resistance and an increase of capacitance. Our data suggest that the lidocaine effects, even at clinical 'sub-blocking' concentrations, could reflect, at least in part, a reversible structural impairment of the axolemma.
Department of Neuroscience and Pharmacology, University of Copenhagen, Copenhagen, Denmark.
Mihai
M
Moldovan
Department of Anesthesia, Nordsjællands Hospital and University of Copenhagen, Copenhagen, Denmark.
Kai Henrik Wiborg
KH
Lange
Department of Neuroscience and Pharmacology, University of Copenhagen, Copenhagen, Denmark.
Niels Jacob
NJ
Aachmann-Andersen
Department of Clinical Neurophysiology, The Neuroscience Center, Copenhagen University Hospital (Rigshospitalet), Copenhagen, Denmark.
Troels Wesenberg
TW
Kjær
Department of Neuroscience and Pharmacology, University of Copenhagen, Copenhagen, Denmark Department of Neuroanesthesia, The Neuroscience Center, Copenhagen University Hospital (Rigshospitalet), Copenhagen, Denmark.
Niels Vidiendal
NV
Olsen
Department of Neuroscience and Pharmacology, University of Copenhagen, Copenhagen, Denmark Department of Clinical Neurophysiology, The Neuroscience Center, Copenhagen University Hospital (Rigshospitalet), Copenhagen, Denmark christian.krarup@regionh.dk.
Christian
C
Krarup
D000328:Adult; D000772:Anesthesia, Local; D000779:Anesthetics, Local / Q000494:pharmacology*; D001369:Axons / Q000187:drug effects* / Q000502:physiology; D002462:Cell Membrane / Q000187:drug effects*; D005260:Female; D006801:Humans; D008012:Lidocaine / Q000494:pharmacology*; D008297:Male; D008959:Models, Neurological; D009046:Motor Neurons / Q000187:drug effects / Q000502:physiology; D018482:Muscle, Skeletal / Q000294:innervation; D009431:Neural Conduction; D061567:Voltage-Gated Sodium Channel Blockers / Q000494:pharmacology*
D000779:Anesthetics, Local; D061567:Voltage-Gated Sodium Channel Blockers; D008012:Lidocaine