Potassium and caffeine contractures of mouse muscles before and after fatiguing stimulation

Authors

  • Dr. Murali Pagala PhD,

    Corresponding author
    1. Neuromuscular Disease Division, Department of Medicine, Maimonides Medical Center, and SUNY Health Sciences Center, Brooklyn, New York
    • Neuromuscular Disease Division, Maimonides Medical Center, 4802 Tenth Avenue, Brooklyn, NY 11219
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  • Kadirimangalam Ravindran PhD,

    1. Neuromuscular Disease Division, Department of Medicine, Maimonides Medical Center, and SUNY Health Sciences Center, Brooklyn, New York
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  • Bellamakonda Amaladevi PhD,

    1. Neuromuscular Disease Division, Department of Medicine, Maimonides Medical Center, and SUNY Health Sciences Center, Brooklyn, New York
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  • Tatsuji Namba MD, PhD,

    1. Neuromuscular Disease Division, Department of Medicine, Maimonides Medical Center, and SUNY Health Sciences Center, Brooklyn, New York
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  • David Grob MD

    1. Neuromuscular Disease Division, Department of Medicine, Maimonides Medical Center, and SUNY Health Sciences Center, Brooklyn, New York
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Abstract

To assess the impairment of muscle membrane excitation, excitation–contraction (E–C) coupling, and contractility during muscle fatigue, we monitored the contracture responses of resting and fatigued muscles on exposure to high potassium and caffeine. On exposure to 140 mmol/L potassium, mouse extensor digitorum longus (EDL) developed a contracture which was 15.7% of tetanic tension before fatigue and 31.7% after fatigue, while soleus developed 59.4% contracture before and 68.8% after fatigue. Potassium causes contractures by depolarizing the muscle fiber membrane. Hence, membrane excitation is reduced in fatigued EDL and soleus. On exposure to 32 mmol/L caffeine, the contracture was 7.1% in resting EDL, 8.5% in fatigued EDL, 50.1% in resting soleus, and 43.7% in fatigued soleus. On exposure to 1 mmol/L caffeine followed by rapid cooling, the contracture was 3.0% in resting EDL, 3.2% in fatigued EDL, 21.5% in resting soleus, and 10.3% in fatigued soleus. Caffeine causes contracture by releasing Ca+ + from the sarcoplasmic reticulum. Our results indicate reduced E–C coupling attributable to reduced membrane excitation in fatigued EDL, and reduced contractility in fatigued soleus. © 1994 John Wiley & Sons, Inc.

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