Multimeric structure of CIC-1 chloride channel revealed by mutations in dominant myotonia congenita (Thomsen)

Abstract

Voltage-gated CIC chloride channels play important roles in cell volume regulation, control of muscle excitability, and probably transepithelial transport. CIC channels can be functionally expressed without other subunits, but it is unknown whether they function as monomers. We now exploit the properties of human mutations in the muscle chloride channel, CIC-1, to explore its multimeric structure. This is based on analysis of the dominant negative effects of CIC-1 mutations causing myotonia congenita (MC, Thomsen's disease), including a newly identified mutation (P480L) in Thomsen's own family. In a co-expression assay, Thomsen's mutation dramatically inhibits normal CIC-1 function. A mutation found in Canadian MC families (G230E) has a less pronounced dominant negative effect, which can be explained by functional WT/G230E heterooligomeric channels with altered kinetics and selectivity. Analysis of both mutants shows independently that CIC-1 functions as a homooligomer with most likely four subunits.