Chloride channels with reduced single-channel conductance in recessive myotonia congenita.

Myoballs were cultured from muscle biopsies of patients having Becker-type recessive generalized myotonia (RGM). Single-channel recordings showed that the conductance of the "intermediate" Cl- channel, the Cl- channel having the highest membrane density and accounting for most of the Cl- conductance in myoballs, was reduced to about 50%. All other channel parameters tested, such as gating properties, ion selectivity, and regulatory pathways, were not different from controls. Two other Cl- channel types were only rarely observed and did not seem different from controls. Also, the macroscopic Cl- conductance measured with tight-seal whole-cell recording was smaller than controls, particularly in the positive membrane potential domain. These results might explain myotonia in RGM on the single-channel level.