Andersen's syndrome mutants produce a knockdown of inwardly rectifying K+ channel in mouse skeletal muscle in vivo

Andersen's syndrome (AS) is a rare autosomal disorder that has been defined by the triad of periodic paralysis, cardiac arrhythmia, and developmental anomalies. AS has been directly linked to over 40 different autosomal dominant negative loss-of-function mutations in the KCNJ2 gene, encoding for the tetrameric strong inward rectifying K+ channel K(IR)2.1. While K(IR)2.1 channels have been suggested to contribute to setting the resting membrane potential (RMP) and to control the duration of the action potential (AP) in skeletal and cardiac muscle, the mechanism by which AS mutations produce such complex pathophysiological symptoms is poorly understood. Thus, we use an adenoviral transduction strategy to study in vivo subcellular distribution of wild-type (WT) and AS-associated mutant K(IR)2.1 channels in mouse skeletal muscle. We determined that WT and D71V AS mutant K(IR)2.1 channels are localized to the sarcolemma and the transverse tubules (T-tubules) of skeletal muscle fibers, while the a dagger 314-315 AS K(IR)2.1 mutation prevents proper trafficking of the homo- or hetero-meric channel complexes. Whole-cell voltage-clamp recordings in individual skeletal muscle fibers confirmed the reduction of inwardly rectifying K+ current (I-K1) after transduction with a dagger 314-315 K(IR)2.1 as compared to WT channels. Analysis of skeletal muscle function revealed reduced force generation during isometric contraction as well as reduced resistance to muscle fatigue in extensor digitorum longus muscles transduced with AS mutant K(IR)2.1. Together, these results suggest that K(IR)2.1 channels may be involved in the excitation-contraction coupling process required for proper skeletal muscle function. Our findings provide clues to mechanisms associated with periodic paralysis in AS.