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Force generation induced by rapid temperature jumps in intact mammalian (rat) skeletal muscle fibres
Author(s) -
Coupland M. E.,
Ranatunga K. W.
Publication year - 2003
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.1469-7793.2003.00439.x
Subject(s) - skeletal muscle , skeletal muscle fibers , biophysics , anatomy , chemistry , biology
We examined the tension (force) responses induced by rapid temperature jumps (T‐jumps) in electrically stimulated, intact fibre bundles (5–10 fibres, fibre length ∼2 mm) isolated from a foot muscle (flexor hallucis brevis) of the rat; the muscle contains ∼90 % type 2 fast fibres. In steady state experiments, the temperature dependence of the twitch tension was basically similar to that previously described from other fast muscles; the tetanic tension increased 3‐ to 4‐fold in raising the temperature from ∼2 to 35 °C and the relation between the tetanic tension and the reciprocal absolute temperature was sigmoidal with half‐maximal tension at 9.5 °C. A rapid T‐jump of 3–5 °C was induced during a contraction by applying an infrared laser pulse (λ= 1.32 μ, 0.2 ms) to the 50 μl trough containing the fibre bundle immersed in physiological saline. At ∼10 °C, a T‐jump induced a large transient tension rise when applied during the rising phase of a twitch contraction, the amplitude of which decreased when the T‐jump was delayed with respect to the stimulus; a T‐jump probably perturbs an early step in excitation‐contraction coupling. No transient increase was seen when a T‐jump was applied during twitch relaxation. When applied during the plateau of a tetanic contraction a T‐jump induced a tension rise to a higher steady tension level; the tension rise after a T‐jump was 2–3 times faster than the corresponding phase of the initial tension rise in a tetanus. The approach to a new steady tension level after a T‐jump was biphasic with a fast (phase 2b, ∼35 s −1 at 10 °C) and a slow component (phase 3, < 10 s −1 ). The rates of both components increased ( Q 10 ∼3) but their amplitudes decreased with increase of the steady temperature. These results from tetanised intact fibres are consistent with the thesis previously proposed from studies on Ca 2+ ‐activated skinned fibres, that the elementary force generation step in muscle is enhanced by increased temperature; the findings indicate that an endothermic molecular step underlies muscle force generation.