BK channels promote action potential repolarization in skeletal muscle but contribute little to myotonia.

Patients with myotonia congenita suffer from slowed relaxation of muscle (myotonia), due to hyperexcitability caused by loss-of-function mutations in the ClC-1 chloride channel. A recent study suggested that block of large-conductance voltage- and Ca- activated K channels (BK) may be effective as therapy. The mechanism underlying efficacy was suggested to be lessening of the depolarizing effect of build-up of K in t-tubules of muscle during repetitive firing.