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Articles by S. G. Waxman
Total Records ( 2 ) for S. G. Waxman
  C Han , S. D Dib Hajj , Z Lin , Y Li , E. M Eastman , L Tyrrell , X Cao , Y Yang and S. G. Waxman

Inherited erythromelalgia (IEM), an autosomal dominant disorder characterized by severe burning pain in response to mild warmth, has been shown to be caused by gain-of-function mutations of sodium channel Nav1.7 which is preferentially expressed within dorsal root ganglion (DRG) and sympathetic ganglion neurons. Almost all physiologically characterized cases of IEM have been associated with onset in early childhood. Here, we report the voltage-clamp and current-clamp analysis of a new Nav1.7 mutation, Q10R, in a patient with clinical onset of erythromelalgia in the second decade. We show that the mutation in this patient hyperpolarizes activation by only –5.3 mV, a smaller shift than seen with early-onset erythromelalgia mutations, but similar to that of I136V, another mutation that is linked to delayed-onset IEM. Using current-clamp, we show that the expression of Q10R induces hyperexcitability in DRG neurons, but produces an increase in excitability that is smaller than the change produced by I848T, an early-onset erythromelalgia mutation. Our analysis suggests a genotype–phenotype relationship at three levels (clinical, cellular and molecular/ion channel), with mutations that produce smaller effects on sodium channel activation being associated with a smaller degree of DRG neuron excitability and later onset of clinical signs.

  J. A Black , J Newcombe and S. G. Waxman

Astrocytes are prominent participants in the response of the central nervous system to injury, including neuroinflammatory insults. Rodent astrocytes in vitro have been shown to express voltage-gated sodium channels in a dynamic manner, with a switch in expression of tetrodotoxin-sensitive to tetrodotoxin-resistant channels in reactive astrocytes. However, the expression of sodium channels in human astrocytes has not been studied, and it is not known whether there are changes in the expression of sodium channels in reactive astrocytes of the human central nervous system. Here, we demonstrate a focal and robust upregulation of sodium channel Nav1.5 in reactive astrocytes at the borders of, and within, active and chronic multiple sclerosis lesions. Nav1.5 was only detectable at very low levels in astrocytes within multiple sclerosis macroscopically normal-appearing white matter or in normal control brain. Nav1.1, Nav1.2, Nav1.3 and Nav1.6 showed little or no expression in astrocytes within normal control tissue and limited upregulation in active multiple sclerosis lesions. Nav1.5 was also expressed at high levels in astrocytes in tissue surrounding new and old cerebrovascular accidents and brain tumours. These results demonstrate the expression of Nav1.5 in human astrocytes and show that Nav1.5 expression is dynamic in these cells. Our observations suggest that the upregulated expression of Nav1.5 in astrocytes may provide a compensatory mechanism, which supports sodium/potassium pump-dependent ionic homoeostasis in areas of central nervous system injury.

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