The myotonia congenita mutation A331T confers a novel hyperpolarization-activated gate to the muscle chloride channel ClC-1.
Mutations in the muscle chloride channel gene CLCN1 cause myotonia congenita, an inherited disorder of skeletal muscle excitability leading to a delayed relaxation after muscle contraction. Here, we examine the functional consequences of a novel disease-causing mutation that predicts the substitution of alanine by threonine at position 331 (A331T) by whole-cell patch-clamp recording of recombinant mutant channels. A331T hClC-1 channels exhibit a novel slow gate that activates during membrane hyperpolarization and closes at positive potentials. This novel gate acts in series with fast opening and closing transitions that are common to wild-type (WT) and mutant channels. Under conditions at which this novel gate is not activated, i.e., a holding potential of 0 mV, the typical depolarization-induced activation gating of WT hClC-1 was only slightly affected by the mutation. In contrast, A331T hClC-1 channels with an open slow gate display an altered voltage dependence of open probability. These novel gating features of mutant channels produce a decreased open probability at -85 mV, the normal muscle resting potential, leading to a reduced resting chloride conductance of affected muscle fibers. The A331T mutation causes an unprecedented alteration of ClC-1 gating and reveals novel processes defining transitions between open and closed states in ClC chloride channels.
Institute of Physiology, Rheinisch-Westfälische Technische Hochschule Aachen, 52057 Aachen, Germany.
Maike
M
Warnstedt
Chen
C
Sun
Barbara
B
Poser
Maria Jose
MJ
Escriva
Lisbeth
L
Tranebjaerg
Torberg
T
Torbergsen
Marijke
M
van Ghelue
Christoph
C
Fahlke
D000328:Adult; D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D002460:Cell Line; D018118:Chloride Channels / Q000235:genetics* / Q000378:metabolism*; D017124:Conserved Sequence; D019281:Dimerization; D015870:Gene Expression; D006579:Heterozygote; D006801:Humans; D015640:Ion Channel Gating / Q000502:physiology; D007668:Kidney / Q000166:cytology / Q000378:metabolism; D008297:Male; D008564:Membrane Potentials; D008969:Molecular Sequence Data; D009154:Mutation; D009224:Myotonia Congenita / Q000235:genetics* / Q000503:physiopathology*; D018408:Patch-Clamp Techniques; D014162:Transfection
C086321:CLC-1 channel; D018118:Chloride Channels