Sodium channel NaV1.9 mutations associated with insensitivity to pain dampen neuronal excitability
Jianying Huang, Carlos G. Vanoye, Alison Cutts, Y. Paul Goldberg, Sulayman D. Dib-Hajj, Charles J. Cohen, Stephen G. Waxman, Alfred L. George Jr.
Jianying Huang, Carlos G. Vanoye, Alison Cutts, Y. Paul Goldberg, Sulayman D. Dib-Hajj, Charles J. Cohen, Stephen G. Waxman, Alfred L. George Jr.
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Research Article Neuroscience

Sodium channel NaV1.9 mutations associated with insensitivity to pain dampen neuronal excitability

Abstract

Voltage-gated sodium channel (NaV) mutations cause genetic pain disorders that range from severe paroxysmal pain to a congenital inability to sense pain. Previous studies on NaV1.7 and NaV1.8 established clear relationships between perturbations in channel function and divergent clinical phenotypes. By contrast, studies of NaV1.9 mutations have not revealed a clear relationship of channel dysfunction with the associated and contrasting clinical phenotypes. Here, we have elucidated the functional consequences of a NaV1.9 mutation (L1302F) that is associated with insensitivity to pain. We investigated the effects of L1302F and a previously reported mutation (L811P) on neuronal excitability. In transfected heterologous cells, the L1302F mutation caused a large hyperpolarizing shift in the voltage-dependence of activation, leading to substantially enhanced overlap between activation and steady-state inactivation relationships. In transfected small rat dorsal root ganglion neurons, expression of L1302F and L811P evoked large depolarizations of the resting membrane potential and impaired action potential generation. Therefore, our findings implicate a cellular loss of function as the basis for impaired pain sensation. We further demonstrated that a U-shaped relationship between the resting potential and the neuronal action potential threshold explains why NaV1.9 mutations that evoke small degrees of membrane depolarization cause hyperexcitability and familial episodic pain disorder or painful neuropathy, while mutations evoking larger membrane depolarizations cause hypoexcitability and insensitivity to pain.

Authors

Jianying Huang, Carlos G. Vanoye, Alison Cutts, Y. Paul Goldberg, Sulayman D. Dib-Hajj, Charles J. Cohen, Stephen G. Waxman, Alfred L. George Jr.

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Figure 4

Effects of mutant channels on the RMP in small DRG neurons.

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Effects of mutant channels on the RMP in small DRG neurons. (A) Scatter-...
(A) Scatter-plot of the RMP recording from neurons expressing either WT or L1302F NaV1.9 channels. ***P < 0.001, by t test. Solid orange circles indicate cells that did not fire all-or-none action potentials in response to external stimuli at their native resting potentials (–24.2 mV, –26.6 mV, –31.9 mV, and –32.7 mV, respectively) but regained excitability when held at –60 mV. (B) Representative action potential in a small DRG neuron overexpressing WT channels evoked when the current injection reached 280 pA. The native resting potential for this neuron was –57.2 mV. (C) Small DRG neuron with a RMP of –26.6 mV (indicated by an arrow in panel A) did not fire action potentials in response to 200-ms current injections from 0 to 500 pA in 100-pA increments. (D) When held at –60 mV, the same neuron as that depicted in C produced subthreshold depolarizations in responses to 30-pA and 35-pA current injections and generated action potentials with a threshold current of 40 pA. (E) Scatter-plot of the RMP in neurons overexpressing either WT or L811P NaV1.9 channels. ***P < 0.001, by t test. Four cells indicated by solid purple diamonds did not fire action potentials in response to external stimuli at their native resting potentials (–20.5 mV, –22.7 mV, –27.2 mV, and –32.9 mV, respectively), but fired spontaneously when held at –60 mV (illustrated in panel F). The cell indicated by the arrow had a RMP of –32.9 mV. (F) Representative spontaneous firing from a holding potential of –60 mV recorded from the cell marked by an arrow in E.