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Functional characterization and cold sensitivity of T1313A, a new mutation of the skeletal muscle sodium channel causing paramyotonia congenita in humans
Author(s) -
Bouhours Magali,
Sternberg Damien,
Davoine ClaireSophie,
Xavier Ferrer,
Willer Jean Claude,
Fontaine Bertrand,
Tabti Nacira
Publication year - 2004
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.2003.053082
Subject(s) - sodium channel , gating , skeletal muscle , missense mutation , mutation , mutant , chemistry , biophysics , cold sensitivity , protein subunit , mexiletine , patch clamp , microbiology and biotechnology , biochemistry , biology , medicine , endocrinology , sodium , gene , receptor , organic chemistry
Paramyotonia congenita (PC) is a dominantly inherited skeletal muscle disorder caused by missense mutations in the SCN4A gene encoding the pore‐forming α subunit (hSkM1) of the skeletal muscle Na + channel. Muscle stiffness is the predominant clinical symptom. It is usually induced by exposure to cold and is aggravated by exercise. The most prevalent PC mutations occur at T1313 on DIII–DIV linker, and at R1448 on DIV–S4 of the α subunit. Only one substitution has been described at T1313 (T1313M), whereas four distinct amino‐acid substitutions were found at R1448 (R1448C/H/P/S). We report herein a novel mutation at position 1313 (T1313A) associated with a typical phenotype of PC. We stably expressed T1313A or wild‐type (hSkM1) channels in HEK293 cells, and performed a detailed study on mutant channel gating defects using the whole‐cell configuration of the patch‐clamp technique. T1313A mutation impaired Na + channel fast inactivation: it slowed and reduced the voltage sensitivity of the kinetics, accelerated the recovery, and decreased the voltage‐dependence of the steady state. Slow inactivation was slightly enhanced by the T1313A mutation: the voltage dependence was shifted toward hyperpolarization and its steepness was reduced compared to wild‐type. Deactivation from the open state assessed by the tail current decay was only slowed at positive potentials. This may be an indirect consequence of disrupted fast inactivation. Deactivation from the inactivation state was hastened. The T1313A mutation did not modify the temperature sensitivity of the Na + channel per se . However, gating kinetics of the mutant channels were further slowed with cooling, and reached levels that may represent the threshold for myotonia. In conclusion, our results confirm the role of T1313 residue in Na + channel fast inactivation, and unveil subtle changes in other gating processes that may influence the clinical phenotype.