Compromised function in the Na(v)1.2 Dravet syndrome mutation R1312T.
Ion channels, specifically voltage-gated sodium channels (Na(v)s), are common culprits in inheritable seizure disorders. Some Na(v) isoforms are particularly susceptible, while others are only weakly associated with neuronal hyperexcitability. Representative of the latter group is Na(v)1.2 (gene name SCN2A): despite its abundance in the brain, Na(v)1.2-related epilepsy is rare and only few studies have been conducted as to the pathophysiological basis of Na(v)1.2 in neuronal hyperexcitability. We here present a detailed functional analysis of Na(v)1.2 mutant, R1312T, which was originally found in a child with Dravet syndrome (formerly known as severe myoclonic epilepsy of infancy or SMEI). Whole-cell voltage clamp analysis revealed clearly compromised function: the mutant channels fast- and slow-inactivated at markedly more negative potentials and recovered from fast inactivation more slowly, which resulted in a use-dependent current reduction to less than 50% of wildtype levels. We also noted a small hyperpolarizing shift in the voltage dependence of activation. Our findings expand the spectrum of abnormal Na(v) channel behavior in epilepsy and raise the question as to how loss-of-function in a sodium channel predominantly expressed in excitatory neurons can lead to hyperexcitability.
Department of Neurology, School of Medicine, University of California-Davis, CA, USA. lossinc@gmail.com
Christoph
C
Lossin
Xiuyu
X
Shi
Michael A
MA
Rogawski
Shinichi
S
Hirose
D001120:Arginine / Q000235:genetics*; D055592:Biophysical Phenomena / Q000235:genetics*; D004558:Electric Stimulation; D004831:Epilepsies, Myoclonic / Q000235:genetics*; D057809:HEK293 Cells; D006801:Humans; D015640:Ion Channel Gating / Q000235:genetics; D008564:Membrane Potentials / Q000235:genetics; D016297:Mutagenesis, Site-Directed / Q000379:methods; D009154:Mutation / Q000235:genetics*; D062551:NAV1.2 Voltage-Gated Sodium Channel / Q000235:genetics*; D018408:Patch-Clamp Techniques; D013912:Threonine / Q000235:genetics*; D013997:Time Factors; D014162:Transfection
D062551:NAV1.2 Voltage-Gated Sodium Channel; D013912:Threonine; D001120:Arginine