1. |
- Kist, Andreas M., et al.
(author)
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SCN10A Mutation in a Patient with Erythromelalgia Enhances C-Fiber Activity Dependent Slowing
- 2016
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In: PLOS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 11:9
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Journal article (peer-reviewed)abstract
- Gain-of-function mutations in the tetrodotoxin (TTX) sensitive voltage-gated sodium channel (Nav) Nav1.7 have been identified as a key mechanism underlying chronic pain in inherited erythromelalgia. Mutations in TTX resistant channels, such as Nav1.8 or Nav1.9, were recently connected with inherited chronic pain syndromes. Here, we investigated the effects of the p.M650K mutation in Nav1.8 in a 53 year old patient with erythromelalgia by micro-neurography and patch-clamp techniques. Recordings of the patient's peripheral nerve fibers showed increased activity dependent slowing (ADS) in CMi and less spontaneous firing compared to a control group of erythromelalgia patients without Nav mutations. To evaluate the impact of the p. M650K mutation on neuronal firing and channel gating, we performed current and voltage-clamp recordings on transfected sensory neurons (DRGs) and neuroblastoma cells. The p. M650K mutation shifted steady-state fast inactivation of Nav1.8 to more hyperpolarized potentials and did not significantly alter any other tested gating behaviors. The AP half-width was significantly broader and the stimulated action potential firing rate was reduced for M650K transfected DRGs compared to WT. We discuss the potential link between enhanced steady state fast inactivation, broader action potential width and the potential physiological consequences.
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2. |
- Kleggetveit, Inge Petter, et al.
(author)
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High spontaneous activity of C-nociceptors in painful polyneuropathy
- 2012
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In: Pain. - : Ovid Technologies (Wolters Kluwer Health). - 0304-3959 .- 1872-6623. ; 153:10, s. 2040-2047
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Journal article (peer-reviewed)abstract
- Polyneuropathy can be linked to chronic pain but also to reduced pain sensitivity. We investigated peripheral C-nociceptors in painful and painless polyneuropathy patients to identify pain-specific changes. Eleven polyneuropathy patients with persistent spontaneous pain and 8 polyneuropathy patients without spontaneous pain were investigated by routine clinical methods. For a specific examination of nociceptor function, action potentials from single C-fibres including 214 C-nociceptors were recorded by microneurography. Patients with and without pain were distinguished by the occurrence of spontaneous activity and mechanical sensitization in C-nociceptors. The mean percentage of C-nociceptors being spontaneously active or mechanically sensitized was significantly higher in patients with pain (mean 40.5% and 14.6%, respectively, P = .02). The difference was mainly due to more spontaneously active mechanoinsensitive C-nociceptors (operationally defined by their mechanical insensitivity and their axonal characteristics) in the pain patients (19 of 56 vs 6 of 43; P = .02). The percentage of sensitized mechanoinsensitive C-nociceptors correlated to the percentage of spontaneously active mechanoinsensitive C-nociceptors (Kendall's tau = .55, P = .004). Moreover, spontaneous activity of mechanoinsensitive C-nociceptors correlated to less pronounced activity-dependent slowing of conduction (Kendall's tau = -.48, P = .009), suggesting that axons were included in the sensitization process. Hyperexcitability in mechanoinsensitive C-nociceptors was significantly higher in patients with polyneuropathy and pain compared to patients with polyneuropathy without pain, while the difference was much less prominent in mechanosensitive (polymodal) C-nociceptors. This hyperexcitability may be a major underlying mechanism for the pain experienced by patients with painful peripheral neuropathy.
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3. |
- Namer, Barbara, et al.
(author)
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Specific changes in conduction velocity recovery cycles of single nociceptors in a patient with erythromelalgia with the I848T gain-of-function mutation of Na(v)1.7
- 2015
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In: Pain. - : Ovid Technologies (Wolters Kluwer Health). - 0304-3959 .- 1872-6623. ; 156:9, s. 1637-1646
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Journal article (peer-reviewed)abstract
- Seven patients diagnosed with erythromelalgia (EM) were investigated by microneurography to record from unmyelinated nerve fibers in the peroneal nerve. Two patients had characterized variants of sodium channel Na(v)1.7 (I848T, I228M), whereas no mutations of coding regions of Na(v)s were found in 5 patients with EM. Irrespective of Na(v)1.7 mutations, more than 50% of the silent nociceptors in the patients with EM showed spontaneous activity. In the patient with mutation I848T, all nociceptors, but not sympathetic efferents, displayed enhanced early subnormal conduction in the velocity recovery cycles and the expected late subnormality was reversed to supranormal conduction. The larger hyperpolarizing shift of activation might explain the difference to the I228M mutation. Sympathetic fibers that lack Na(v)1.8 did not show supranormal conduction in the patient carrying the I848T mutation, confirming in human subjects that the presence of Na(v)1.8 crucially modulates conduction in cells expressing EM mutant channels. The characteristic pattern of changes in conduction velocity observed in the patient with the I848T gain-of function mutation in Na(v)1.7 could be explained by axonal depolarization and concomitant inactivation of Na(v)1.7. If this were true, activity-dependent hyperpolarization would reverse inactivation of Na(v)1.7 and account for the supranormal CV. This mechanism might explain normal pain thresholds under resting conditions.
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