The effects of repeated active stretches on tension generation and myoplasmic calcium in frog single muscle fibres.

The effects of repeated active stretches on tension generation and myoplasmic calcium in frog... 1. A series of contractions with stretches (eccentric contractions) beyond the optimal length for tension generation (optimum) were shown to induce a shift in that optimum in single muscle fibres of frog, as has been previously reported for whole muscles. Shifts averaging 0.129 micron (sarcomere)‐1 or 6% were found, without apparent damage to the fibre. 2. The stiffness of fibres was found to fall during a stretch, even though tension was rising. In addition, the isometric stiffness fell as a result of a series of eccentric contractions. 3. Calcium‐sensitive fluorescent dyes indicated that such contractions did not reduce the amplitude of the intracellular calcium transient, but did increase its duration. A rise in resting (Ca2+) was found to accompany damage, but not necessarily the shift in optimum. 4. The twitch potentiator nitrate was shown to increase myoplasmic (Ca2+) during twitch and tetani, but not to reverse the shift in optimum length due to eccentric contractions. Both eccentric contractions and twitch potentiation reduced the maximum stimulation rate to which a fibre could respond with propagated action potentials. 5. These results exclude reduced myoplasmic (Ca2+) as the cause of the shift in optimum length in this preparation. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png The Journal of Physiology Wiley

The effects of repeated active stretches on tension generation and myoplasmic calcium in frog single muscle fibres.

The Journal of Physiology, Volume 497 (3) – Dec 15, 1996

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Publisher
Wiley
Copyright
© 2014 The Physiological Society
ISSN
0022-3751
eISSN
1469-7793
DOI
10.1113/jphysiol.1996.sp021798
Publisher site
See Article on Publisher Site

Abstract

1. A series of contractions with stretches (eccentric contractions) beyond the optimal length for tension generation (optimum) were shown to induce a shift in that optimum in single muscle fibres of frog, as has been previously reported for whole muscles. Shifts averaging 0.129 micron (sarcomere)‐1 or 6% were found, without apparent damage to the fibre. 2. The stiffness of fibres was found to fall during a stretch, even though tension was rising. In addition, the isometric stiffness fell as a result of a series of eccentric contractions. 3. Calcium‐sensitive fluorescent dyes indicated that such contractions did not reduce the amplitude of the intracellular calcium transient, but did increase its duration. A rise in resting (Ca2+) was found to accompany damage, but not necessarily the shift in optimum. 4. The twitch potentiator nitrate was shown to increase myoplasmic (Ca2+) during twitch and tetani, but not to reverse the shift in optimum length due to eccentric contractions. Both eccentric contractions and twitch potentiation reduced the maximum stimulation rate to which a fibre could respond with propagated action potentials. 5. These results exclude reduced myoplasmic (Ca2+) as the cause of the shift in optimum length in this preparation.

Journal

The Journal of PhysiologyWiley

Published: Dec 15, 1996

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