title: Dynamic-clamp analysis of wild-type human Nav1.7 and erythromelalgia mutant channel L858H.
abstract: The link between sodium channel Nav1.7 and pain has been strengthened by identification of gain-of-function mutations in patients with inherited erythromelalgia (IEM), a genetic model of neuropathic pain in humans. A firm mechanistic link to nociceptor dysfunction has been precluded because assessments of the effect of the mutations on nociceptor function have thus far depended on electrophysiological recordings from dorsal root ganglia (DRG) neurons transfected with wild-type (WT) or mutant Nav1.7 channels, which do not permit accurate calibration of the level of Nav1.7 channel expression. Here, we report an analysis of the function of WT Nav1.7 and IEM L858H mutation within small DRG neurons using dynamic-clamp. We describe the functional relationship between current threshold for action potential generation and the level of WT Nav1.7 conductance in primary nociceptive neurons and demonstrate the basis for hyperexcitability at physiologically relevant levels of L858H channel conductance. We demonstrate that the L858H mutation, when modeled using dynamic-clamp at physiological levels within DRG neurons, produces a dramatically enhanced persistent current, resulting in 27-fold amplification of net sodium influx during subthreshold depolarizations and even greater amplification during interspike intervals, which provide a mechanistic basis for reduced current threshold and enhanced action potential firing probability. These results show, for the first time, a linear correlation between the level of Nav1.7 conductance and current threshold in DRG neurons. Our observations demonstrate changes in sodium influx that provide a mechanistic link between the altered biophysical properties of a mutant Nav1.7 channel and nociceptor hyperexcitability underlying the pain phenotype in IEM.
authors.affiliation: Department of Neurology and Center for Neuroscience and Regeneration Research, Yale University School of Medicine, New Haven, Connecticut; and.
authors.forename: Dmytro V
authors.initials: DV
authors.lastname: Vasylyev
authors.forename: Chongyang
authors.initials: C
authors.lastname: Han
authors.forename: Peng
authors.initials: P
authors.lastname: Zhao
authors.forename: Sulayman
authors.initials: S
authors.lastname: Dib-Hajj
authors.forename: Stephen G
authors.initials: SG
authors.lastname: Waxman
mesh_terms: D000818:Animals; D001703:Biophysics; D002478:Cells, Cultured; D004558:Electric Stimulation; D004916:Erythromelalgia / Q000235:genetics*; D005727:Ganglia, Spinal / Q000166:cytology; D057809:HEK293 Cells; D006801:Humans; D008564:Membrane Potentials / Q000187:drug effects / Q000235:genetics*; D051379:Mice; D018345:Mice, Knockout; D008954:Models, Biological; D009154:Mutation / Q000235:genetics*; D062556:NAV1.7 Voltage-Gated Sodium Channel / Q000235:genetics*; D009431:Neural Conduction; D009474:Neurons / Q000187:drug effects / Q000502:physiology*; D018408:Patch-Clamp Techniques; D026941:Sodium Channel Blockers / Q000494:pharmacology; D013779:Tetrodotoxin / Q000494:pharmacology; D014162:Transfection
chemical_list: D062556:NAV1.7 Voltage-Gated Sodium Channel; C486866:SCN9A protein, human; D026941:Sodium Channel Blockers; D013779:Tetrodotoxin
keywords: Hodgkin-Huxley equations; channelopathy; dynamic-clamp; pain; sodium channel