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In vivo assessment of muscle membrane properties in the sodium channel myotonias
Author(s) -
Tan S. Veronica,
Z'Graggen Werner J.,
Hanna Michael G.,
Bostock Hugh
Publication year - 2018
Publication title -
muscle and nerve
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.025
H-Index - 145
eISSN - 1097-4598
pISSN - 0148-639X
DOI - 10.1002/mus.25956
Subject(s) - sodium channel , refractory period , myotonia , sodium , chemistry , medicine , endocrinology , mexiletine , membrane potential , sodium channel blocker , in vivo , myotonia congenita , biophysics , biology , biochemistry , genetics , organic chemistry , myotonic dystrophy
The gain‐of‐function mutations that underlie sodium channel myotonia (SCM) and paramyotonia congenital (PMC) produce differing clinical phenotypes. We used muscle velocity recovery cycles (MVRCs) to investigate membrane properties. Methods MVRCs and responses to trains of stimuli were compared in patients with SCM ( n = 9), PMC ( n = 8), and normal controls ( n = 26). Results The muscle relative refractory period was reduced in SCM, consistent with faster recovery of the mutant sodium channels from inactivation. Both SCM and PMC showed an increased early supernormality and increased mean supernormality following multiple conditioning stimuli, consistent with slowed sodium channel inactivation. Trains of fast impulses caused a loss of amplitude in PMC, after which only half of the muscle fibers recovered, suggesting that the remainder stayed depolarized by persistent sodium currents. Discussion The differing effects of mutations on sodium channel function can be demonstrated in human subjects in vivo using this technique. Muscle Nerve 57 : 586–594, 2018