title: Characterization of two new dominant ClC-1 channel mutations associated with myotonia.
abstract: Voltage-gated ClC-1 chloride channels encoded by the CLCN1 gene have a major role in setting the membrane potential in skeletal muscle. More than 60 CLCN1 mutations have been associated with myotonia congenita. These mutations are traditionally classified as recessive (Becker's disease) or dominant (Thomsen's disease). In this study, we have electrophysiologically characterized two new dominant ClC-1 mutations, thereby elucidating the observed phenotype in patients. The two ClC-1 mutants M128V and E193K were identified, and the DNA was isolated from patients and subsequently expressed in Xenopus laevis oocytes for electrophysiological characterization. Both ClC-1 mutants, M128V and E193K, showed a large rightward shift in the current-voltage relationship. In addition, the activation kinetics were slowed in the ClC-1 M128V mutant, as compared to the wild-type ClC-1. Interestingly, ClC-1 E193K revealed a change in reversal potential compared to wild-type channels. This finding supports the notion that the E193 amino acid is an important determinant in the selectivity filter of the human ClC-1 channel. The electrophysiological behavior of both mutants demonstrates a severe reduction in ClC-1 channel conductance under physiologically relevant membrane potentials. These studies thereby explain the molecular background for the observed myotonia in patients.
authors.affiliation: Department of Medical Physiology, The Panum Institute, University of Copenhagen, Blegdamsvej 3, DK-2200 Copenhagen N, Denmark. mgrunnet@mfi.ku.dk
authors.forename: Morten
authors.initials: M
authors.lastname: Grunnet
authors.forename: Thomas
authors.initials: T
authors.lastname: Jespersen
authors.forename: Eskild
authors.initials: E
authors.lastname: Colding-Jørgensen
authors.forename: Marianne
authors.initials: M
authors.lastname: Schwartz
authors.forename: Dan A
authors.initials: DA
authors.lastname: Klaerke
authors.forename: John
authors.initials: J
authors.lastname: Vissing
authors.forename: Søren-Peter
authors.initials: SP
authors.lastname: Olesen
authors.forename: Morten
authors.initials: M
authors.lastname: Dunø
mesh_terms: D000328:Adult; D000595:Amino Acid Sequence; D000818:Animals; D002648:Child; D018118:Chloride Channels / Q000235:genetics*; D004594:Electrophysiology; D005260:Female; D005799:Genes, Dominant / Q000235:genetics; D005822:Genetic Vectors; D006801:Humans; D015640:Ion Channel Gating / Q000235:genetics / Q000502:physiology; D008297:Male; D008969:Molecular Sequence Data; D009154:Mutation / Q000235:genetics* / Q000502:physiology; D009222:Myotonia / Q000235:genetics* / Q000503:physiopathology; D009865:Oocytes / Q000378:metabolism; D018408:Patch-Clamp Techniques; D010375:Pedigree; D014158:Transcription, Genetic; D014982:Xenopus laevis
chemical_list: C086321:CLC-1 channel; D018118:Chloride Channels