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Nav1.4 slow-inactivation: Is it a player in the warm-up phenomenon of myotonic disorders?

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Correspondence to: C. Lossin; e-mail: lossinc@gmail.com

Abstract

Myotonia is a heritable disorder in which patients are unable to willfully relax their muscles. The physiological basis for myotonia lies in well-established deficiencies of skeletal muscle chloride and sodium conductances. What is unclear is how normal muscle function can temporarily return with repeated movement, the so-called “warm-up” phenomenon. Electrophysiological analyses of the skeletal muscle voltage-gated sodium channel Nav1.4 (gene name SCN4A), a key player in myotonia, have revealed several parallels between the Nav1.4 biophysical signature, specifically slow-inactivation, and myotonic warm-up, which suggest that Nav1.4 is critical not only in producing the myotonic reaction, but also in mediating the warm-up. Muscle Nerve, 2013

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