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The role of calcium stores in fatigue of isolated single muscle fibres from the cane toad
Author(s) -
Kabbara A. A.,
Allen D. G.
Publication year - 1999
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 - 10.1111/j.1469-7793.1999.0169o.x
Subject(s) - calcium , chemistry , toad , bufo marinus , extracellular , biophysics , zoology , caffeine , muscle fatigue , anatomy , medicine , endocrinology , biochemistry , biology , electromyography , organic chemistry , neuroscience
1 Intracellular calcium ([Ca 2+ ] i ) and tension were measured from single muscle fibres dissected from the cane toad ( Bufo marinus ). The amount of Ca 2+ which could be released from the sarcoplasmic reticulum (SR) was estimated by brief (≈20 s) exposures to 4‐chloro‐ m ‐cresol (4‐CmC) or caffeine. 2 Muscle fatigue was produced by repeated tetani at 4 s or shorter intervals and continued until tension had fallen to 50 % of the control. The intracellular free calcium concentration during a tetanus (tetanic [Ca 2+ ] i ) first increased and then steadily declined to 43 ± 2 % of control by the time tension had fallen to 50 %. Over the period of fatigue the rapidly releasable Ca 2+ from the SR fell to 46 ± 6 % of control. Tension and tetanic [Ca 2+ ] i recovered to 93 ± 3 % and 100 ± 4 % of the control values after 20 min of rest. Over the same period rapidly releasable SR Ca 2+ recovered to 98 ± 12 %. 3 When a similar number of tetani (200) were repeated at longer intervals (10 s), fibres showed only a small reduction in tension (to 85 ± 1 %) and tetanic [Ca 2+ ] i did not change significantly. Under these conditions the rapidly releasable SR Ca 2+ did not change significantly. 4 The recovery of rapidly releasable SR Ca 2+ after fatigue was unaffected by removal of extracellular calcium but did not occur when oxidative phosphorylation was inhibited with cyanide. 5 These results suggest that an important cause of the decline of tetanic [Ca 2+ ] i during fatigue is an equivalent decline in the amount of rapidly releasable SR Ca 2+ . The results show that the decline of rapidly releasable SR Ca 2+ is related to a metabolic consequence of fatigue and are consistent with the hypothesis that Ca 2+ precipitates with phosphate in the SR during fatigue.