Targeted mutation of mouse skeletal muscle sodium channel produces myotonia and potassium-sensitive weakness
Lawrence J. Hayward, Joanna S. Kim, Ming-Yang Lee, Hongru Zhou, Ji W. Kim, Kumudini Misra, Mohammad Salajegheh, Fen-fen Wu, Chie Matsuda, Valerie Reid, Didier Cros, Eric P. Hoffman, Jean-Marc Renaud, Stephen C. Cannon, Robert H. Brown Jr.
Lawrence J. Hayward, Joanna S. Kim, Ming-Yang Lee, Hongru Zhou, Ji W. Kim, Kumudini Misra, Mohammad Salajegheh, Fen-fen Wu, Chie Matsuda, Valerie Reid, Didier Cros, Eric P. Hoffman, Jean-Marc Renaud, Stephen C. Cannon, Robert H. Brown Jr.
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Research Article Muscle biology

Targeted mutation of mouse skeletal muscle sodium channel produces myotonia and potassium-sensitive weakness

Abstract

Hyperkalemic periodic paralysis (HyperKPP) produces myotonia and attacks of muscle weakness triggered by rest after exercise or by K+ ingestion. We introduced a missense substitution corresponding to a human familial HyperKPP mutation (Met1592Val) into the mouse gene encoding the skeletal muscle voltage-gated Na+ channel NaV1.4. Mice heterozygous for this mutation exhibited prominent myotonia at rest and muscle fiber-type switching to a more oxidative phenotype compared with controls. Isolated mutant extensor digitorum longus muscles were abnormally sensitive to the Na+/K+ pump inhibitor ouabain and exhibited age-dependent changes, including delayed relaxation and altered generation of tetanic force. Moreover, rapid and sustained weakness of isolated mutant muscles was induced when the extracellular K+ concentration was increased from 4 mM to 10 mM, a level observed in the muscle interstitium of humans during exercise. Mutant muscle recovered from stimulation-induced fatigue more slowly than did control muscle, and the extent of recovery was decreased in the presence of high extracellular K+ levels. These findings demonstrate that expression of the Met1592Val Na+ channel in mouse muscle is sufficient to produce important features of HyperKPP, including myotonia, K+-sensitive paralysis, and susceptibility to delayed weakness during recovery from fatigue.

Authors

Lawrence J. Hayward, Joanna S. Kim, Ming-Yang Lee, Hongru Zhou, Ji W. Kim, Kumudini Misra, Mohammad Salajegheh, Fen-fen Wu, Chie Matsuda, Valerie Reid, Didier Cros, Eric P. Hoffman, Jean-Marc Renaud, Stephen C. Cannon, Robert H. Brown Jr.

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Figure 8

Mutant (+/m) EDL fatigued more slowly than control (+/+) muscle and was more vulnerable to impaired recovery in elevated [K+]o.

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Mutant (+/m) EDL fatigued more slowly than control (+/+) muscle and was ...
(A–C) Fatigue was induced by continuous 100-Hz stimulation to isolated EDL muscles using 1-ms pulses in bath that contained 4 mM [K+] and 2 mM [Ca2+]. (A) In the left panel, tetanic force was normalized to the peak value, and the responses (mean ± SD, dashed lines) are shown for EDL from (+/m) mice (n = 8, 10.8 ± 2.2 months old) or (+/+) mice (n = 5, 11.4 ± 1.8 months old). The time required for decline to 50% of the peak force (fatigue T1/2R) was increased by 2.3-fold for the older mutant mice versus controls and by 1.8-fold for younger mutant mice (n = 6, 4.0 ± 0.7 months old) versus controls (n = 10, 4.2 ± 0.8 months old). (B) Recovery from fatigue for EDL muscles from 8.5 ± 0.4–month-old mutant (n = 6) and sibling controls (n = 5) in normal [K+]. Tetanic stimuli (0.5-ms, 70-mA current pulses for 300 ms at 125 Hz) were applied before and after 100-Hz stimulation (small blue box), and the normalized responses (mean ± SEM) are shown. The time required to regain 50% of the full extent of recovery (recovery T1/2R) was increased by 2.8-fold for mutant compared with control. (C) Stimulation of EDL muscles to fatigue as in B was followed by exposure to a bath containing 10 mM [K+] and 0.5 mM [Ca2+], which impaired the extent of recovery for mutant more than control muscles. Weakness was reversible in recovery buffer, and mutant muscles regained force 1.9-fold faster than did control muscle. Gray bars in the left panels indicate significant differences by ANOVA (P < 0.05) between mutant (red circles) and control (open squares) responses. The bar graphs in the right panels show mean ± SEM. *P < 0.005, 2-tailed Student’s t test.