Generalized epilepsy with febrile seizures plus type 2 mutation W1204R alters voltage-dependent gating of Nav1.1 sodium channels

Spampanato, J., Escayg, A., Meisler, M. H. and Goldin, A. L. (2003) Generalized epilepsy with febrile seizures plus type 2 mutation W1204R alters voltage-dependent gating of Nav1.1 sodium channels. Neuroscience, 116 1: 37-48. doi:10.1016/S0306-4522(02)00698-X


Author Spampanato, J.
Escayg, A.
Meisler, M. H.
Goldin, A. L.
Title Generalized epilepsy with febrile seizures plus type 2 mutation W1204R alters voltage-dependent gating of Nav1.1 sodium channels
Journal name Neuroscience   Check publisher's open access policy
ISSN 0306-4522
Publication date 2003-01
Sub-type Article (original research)
DOI 10.1016/S0306-4522(02)00698-X
Volume 116
Issue 1
Start page 37
End page 48
Total pages 12
Place of publication Oxford, U.K.
Publisher Pergamon
Language eng
Subject 11 Medical and Health Sciences
1109 Neurosciences
Abstract Nine mutations that cause generalized epilepsy with febrile seizures plus have been identified in the SCN1A gene encoding the α subunit of the Nav1.1 voltage-gated sodium channel. The functional properties of two of these mutations (T875M and R1648H) have previously been described. T875M was shown to enhance slow inactivation, while R1648H dramatically accelerated recovery from inactivation. In this report, we have cloned, expressed and characterized the functional effects of a third generalized epilepsy with febrile seizures plus mutation, W1204R (Am J Hum Genet 68 (2001) 866). The mutation was cloned into the orthologous rat channel, rNav1.1, and at the same time a single base pair insertion at base 120 in the original rNav1.1 clone was corrected. The level of expression of the corrected wild-type rNav1.1 was approximately 1000-fold higher than that of the original clone and comparable to that achieved with other neuronal sodium channels expressed in Xenopus oocytes. The properties of the W1204R mutant in the corrected rNav1.1 were determined in the absence and presence of the β1 subunit in Xenopus oocytes. The W1204R mutation resulted in approximately 11 mV hyperpolarized shifts in the voltage-dependence of activation and steady-state inactivation when expressed as an α subunit alone. When the channels were coexpressed with the β1 subunit, the hyperpolarized shifts were still present but smaller, approximately 5 mV in magnitude. All other properties that we examined were comparable for the mutant and wild-type channels. The negative shift in activation would increase channel excitability, whereas the negative shift in inactivation would decrease excitability. The negative shifts in both properties also shifted the window current, which is the voltage region in which sodium channels can continue to open because some percentage of channels are activated and not all of the channels are inactivated. The shift in window current for the W1204R mutation could result in hyperexcitability because the neuron’s potential is more likely to reach the more negative range. These results demonstrate that a third SCN1A mutation that causes generalized epilepsy with febrile seizures plus 2 alters the properties of the sodium channel in a different manner than the previous two mutations that were studied. The diversity in functional effects for these three mutations indicates that a similar clinical phenotype can result from very different underlying sodium channel abnormalities.
Keyword Electrophysiology
GEFS+
SCN1A
Epilepsy
Q-Index Code C1
Q-Index Status Provisional Code
Institutional Status Unknown

Document type: Journal Article
Sub-type: Article (original research)
Collections: Excellence in Research Australia (ERA) - Collection
Queensland Brain Institute Publications
 
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Created: Fri, 18 Dec 2009, 09:15:17 EST by Ms May Balasaize on behalf of Queensland Brain Institute