A gain-of-function mutation in the sodium channel gene Scn2a results in seizures and behavioral abnormalities
Section snippets
Transgene constructs
Plasmid pNSE-Ex4 containing the 4 kb promoter fragment from the rat NSE gene that includes 2.8 kb of flanking sequence, exon 1, intron 1 and 6 bp of exon 215 was provided by J. G. Sutcliffe (Scripps Institute, La Jolla, CA). Plasmid pBS-polyA, containing a 196 bp BamHI fragment from pCMVβ with a SV40 polyadenylation cassette, was provided by J. S. Chamberlain (University of Michigan). The 6.5 kb rat Scn2a cDNA constructs contain the FLAG epitope (DYKDDDDK) immediately downstream of the
Characterization of the GAL879-881QQQ channel in Xenopus oocytes
The mutant channel was characterized in Xenopus oocytes using a cut-open oocyte voltage clamp. The mutant channel inactivated more slowly than the WT channel (Fig. 1A). However, the slower inactivation did not result from a change in the magnitude of the time constants for either the fast or slow component of inactivation, which were similar for the mutant and WT channels during depolarizations ranging from −20 mV to +50 mV. The slower inactivation resulted from a significant decrease in the
Discussion
Sodium currents generated by expression of the GAL879-881QQQ mutant channel in Xenopus oocytes exhibited a slower rate of inactivation than the WT channel, increased percentage of current that inactivated with a slow time constant, and increased persistent current. Very similar sodium currents were detected in hippocampal neurons from Q54 transgenic mice expressing the mutant channel. The increase in persistent current was statistically significant in the neuronal context, in the presence of
Acknowledgements
We thank Julie Jones and Laurie Weiss for advice and assistance, Leslie Sprunger for helpful discussions, and Sally Camper and Roger Albin for review of the manuscript. Supported by NIH grants NS34509 (MHM) and NS26729 (ALG), the Organogenesis Postdoctoral Training Program T32 HD07505 and National Research Service Award NS10692 (JAK), NINDS awards KO8 NS01748 and KO2 NS02081 (JK), and National Multiple Sclerosis Grant RG1912 and grants from the Medical Research Service and Rehabilitation
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