Primary structure and functional expression of a developmentally regulated skeletal muscle chloride channel

Abstract

Skeletal muscle is unusual in that 70-85% of resting membrane conductance is carried by chloride ions. This conductance is essential for membrane-potential stability, as its block by 9-anthracene-carboxylic acid and other drugs causes myotonia. Fish electric organs are developmentally derived from skeletal muscle, suggesting that mammalian muscle may express a homologue of the Torpedo mamorata electroplax chloride channel. We have now cloned the complementary DNA encoding a rat skeletal muscle chloride channel by homology screening to the Cl- channel from Torpedo. It encodes a 994-amino-acid protein which is about 54% identical to the Torpedo channel and is predominantly expressed in skeletal muscle. Messenger RNA amounts in that tissue increase steeply in the first 3-4 weeks after birth, in parallel with the increase in muscle Cl- conductance. Expression from cRNA in Xenopus oocytes leads to 9-anthracene-carboxylic acid-sensitive currents with time and voltage dependence typical for macroscopic muscle Cl- conductance. This and the functional destruction of this channel in mouse myotonia suggests that we have cloned the major skeletal muscle chloride channel.

Expression of chloride channel 1 mRNA in cultured myogenic cells: a marker of myotube maturation

“…Hybridization was performed with the following probes: mouse desmin cDNA (1.5 kB EcoRI fragment [19]; rat CIC-I cDNA (1.4 kB EcoRI/HindlII fragment; nt --83 to nt +1324 [20]); 18S rRNA [ cycles 28 24 20 …”

Myotonia caused by mutations in the muscle chloride channel geneCLCN1

“…A drug that increases the open probability could then increase the Cl conductance of the skeletal muscle and abolish the hyperexcitability. The pharmacological agents that interfere most strongly with CLC-1 are 9-anthracene carboxylic acid (9AC) and the S( ) enantiomer of p-chloro-phenoxy-propionic acid (CPP), both of which inhibit the muscle Cl conductance and CLC-1with an apparent affinity in the 10-50 µM range [Palade and Barchi, 1977;De Luca et al, 1992;Steinmeyer et al, 1991b;Aromataris et al, 1999;Pusch et al, 2000]. CPP and also 9AC are most likely open channel blockers that, in addition, reduce the open probability by impeding channel opening of closed, drug-bound channels [Pusch et al, 2001;Accardi and Pusch, unpublished observations].…”

“…In this short review I will give a brief overview of Cl channel myotonia and summarize the mutations and their effects found in the CLCN1 gene coding for the skeletal muscle voltage-dependent Cl channel [Steinmeyer et al, 1991b;Koch et al, 1992] (MIM# 118425) that lead to general myotonia congenita (GMC).…”

Huntington disease skeletal muscle is hyperexcitable owing to chloride and potassium channel dysfunction

“…If they are reduced, the membrane becomes hyperexcitable, and normally subthreshold events can initiate action potentials and involuntary contractions. Most of the resting conductance in skeletal muscle is mediated by chloride through the muscle chloride channel (ClC-1), and a large decrease in this conductance results in the hyperexcitability, involuntary contractions, rigidity, and persistent contractions that characterize general myotonia at the cellular level (14)(15)(16)(17)(18)(19)(20).…”