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J Neurosci. 2014 Sep 10;34(37):12328-40. doi: 10.1523/JNEUROSCI.2773-14.2014.

Depolarized inactivation overcomes impaired activation to produce DRG neuron hyperexcitability in a Nav1.7 mutation in a patient with distal limb pain.

Author information

1
Department of Neurology and Center for Neuroscience and Regeneration Research, Yale University School of Medicine, New Haven, Connecticut 06510, Rehabilitation Research Center, Veterans Affairs Connecticut Healthcare System, West Haven, Connecticut 06516.
2
Department of Neurology, University Medical Center, Utrecht, The Netherlands, and.
3
Department of Gastroenterology and Hepatology, Radboud University Nijmegen Medical Center, Nijmegen, The Netherlands.
4
Department of Neurology and Center for Neuroscience and Regeneration Research, Yale University School of Medicine, New Haven, Connecticut 06510, Rehabilitation Research Center, Veterans Affairs Connecticut Healthcare System, West Haven, Connecticut 06516, Stephen.Waxman@yale.edu.

Abstract

Sodium channel Nav1.7, encoded by SCN9A, is expressed in DRG neurons and regulates their excitability. Genetic and functional studies have established a critical contribution of Nav1.7 to human pain disorders. We have now characterized a novel Nav1.7 mutation (R1279P) from a female human subject with distal limb pain, in which depolarized fast inactivation overrides impaired activation to produce hyperexcitability and spontaneous firing in DRG neurons. Whole-cell voltage-clamp recordings in human embryonic kidney (HEK) 293 cells demonstrated that R1279P significantly depolarizes steady-state fast-, slow-, and closed-state inactivation. It accelerates deactivation, decelerates inactivation, and facilitates repriming. The mutation increases ramp currents in response to slow depolarizations. Our voltage-clamp analysis showed that R1279P depolarizes channel activation, a change that was supported by our multistate structural modeling. Because this mutation confers both gain-of-function and loss-of-function attributes on the Nav1.7 channel, we tested the impact of R1279P expression on DRG neuron excitability. Current-clamp studies reveal that R1279P depolarizes resting membrane potential, decreases current threshold, and increases firing frequency of evoked action potentials within small DRG neurons. The populations of spontaneously firing and repetitively firing neurons were increased by expressing R1279P. These observations indicate that the dominant proexcitatory gating changes associated with this mutation, including depolarized steady-state fast-, slow-, and closed-state inactivation, faster repriming, and larger ramp currents, override the depolarizing shift of activation, to produce hyperexcitability and spontaneous firing of nociceptive neurons that underlie pain.

KEYWORDS:

DRG neurons; Nav1.7; mutation; pain; sodium channel

PMID:
25209274
PMCID:
PMC6615500
DOI:
10.1523/JNEUROSCI.2773-14.2014
[Indexed for MEDLINE]
Free PMC Article

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