A mutation in autosomal dominant myotonia congenita affects pore properties of the muscle chloride channel.
Autosomal dominant myotonia congenita is an inherited disorder of skeletal muscle caused by mutations in a voltage-gated Cl- channel gene (CLCN1, 7q35). Here, we report that a mutation predicting the substitution of Gly 230 by glutamic acid (G230E) between segments D3 and D4 dramatically alters the pore properties of a recombinant human muscle Cl- channel (hCIC-1) expressed in a mammalian cell line (tsA201). The G230E mutation causes substantial changes in anion and cation selectivity as well as a fundamental change in rectification of the current-voltage relationship. Whereas wild-type channels are characterized by pronounced inward rectification and a Cl > thiocyanate > Br > NO(3) > I > CH(3)SO(3) selectivity, G230E exhibits outward rectification at positive potentials and a thiocyanate > NO(3) > I > Br > Cl > CH(3)SO(3) selectivity. Furthermore, the cation-to-anion permeability ratio of the mutant is much greater than that of the wild-type channel. Voltage-dependent blocks by intracellular and extracellular iodide help to distinguish two distinct ion binding sites within the hClC-1 conduction pathway. Both binding sites are preserved in the mutant but have decreased affinities for iodide. These findings suggest that Gly 230 is critical for normal ion conductance in hClC-1 and that this residue resides within the channel pore.
Fahlke
C
C
Department of Medicine, Vanderbilt University School of Medicine, Nashville, TN 37232, USA.
Beck
C L
CL
George
A L
AL
D000838:Anions; D002460:Cell Line; D018118:Chloride Channels / Q000235:genetics* / Q000502:physiology; D002874:Chromosome Mapping; D002897:Chromosomes, Human, Pair 7; D005799:Genes, Dominant; D006801:Humans; D007454:Iodides / Q000494:pharmacology; D008564:Membrane Potentials / Q000187:drug effects; D018482:Muscle, Skeletal / Q000503:physiopathology*; D009224:Myotonia Congenita / Q000235:genetics / Q000503:physiopathology*; D018408:Patch-Clamp Techniques; D017354:Point Mutation; D011994:Recombinant Proteins / Q000378:metabolism; D013997:Time Factors; D014162:Transfection
D000838:Anions; D018118:Chloride Channels; D007454:Iodides; D011994:Recombinant Proteins