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

Abstract

To assess the impairment of muscle membrane excitation, excitationcontraction (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. 0 1994 John Wiley & Sons, Inc.

Effect of physiological levels of caffeine on Ca2+ handling and fatigue development in Xenopus isolated single myofibers

“…Rather, the plasma caffeine concentration of caffeine in humans is usually between 20 and 50 micromolar with an upper limit of 70 micromolar (17). Furthermore, it has been demonstrated in whole muscle that decreasing the concentration of caffeine results in a drastic reduction in the ability of caffeine to rescue contractile function in fatigued muscle (35). Thus, although the results from studies using supraphysiological concentrations of caffeine do offer some insights about the potential effects that caffeine can have on muscles and, in particular, shed light on the mechanisms of muscle fatigue, these studies do not adequately describe the effects of caffeine in an exercising human.…”

Physiological fatigue of smooth muscle contractions in rat urinary bladder

“…5). High potassium levels depolarize the smooth muscle membrane, and increase the influx of extracellular Ca 2+ through the voltage‐gated Ca‐channels, leading to generation of contractile tension [1,24]. Hence greater generation of tension on exposure of the fatigued bladder strips to high potassium indicates that during fatigue there is a reduction in depolarization of the smooth muscle membranes, and when the depolarizing agent is supplied externally, the bladder muscles generate greater contractile tension.…”

Events of the excitation–contraction–relaxation (E–C–R) cycle in fast‐ and slow‐twitch mammalian muscle fibres relevant to muscle fatigue

“…However, this may not be the case with mammalian fibres which require a larger depolarization than the anuran fibres to respond with maximum contracture (Dulhunty & Gage 1985). Indeed, recent experiments with both fast‐twitch (Pagala et al 1994, Cairns & Dulhunty 1995) and slow‐twitch fibres (Cairns & Dulhunty 1995) confirmed that high‐frequency stimulation‐related depression of the sarcolemmal action potential contributed markedly to incomplete activation and force loss, particularly in fast‐twitch fibres which require the largest depolarization for contractile activation (Dulhunty & Gage 1985).…”