The dependence on extent of shortening of the extra energy liberated by rapidly shortening frog skeletal muscle.

111

ATP consumption and force development were determined in single skinned muscle fibres of the rat at 12 °C. Myofibrillar ATPase consumption was measured photometrically from NADH oxidation which was coupled to ATP hydrolysis. Myosin heavy chain (MHC) and light chain (MLC) isoforms were identified by gel electrophoresis. Slow fibres (n= 14) containing MHCI and fast fibres (n= 18) containing MHCIIB were compared. Maximum shortening velocity was 1.02 ± 0.63 and 3.05 ± 0.23 lengths s−1, maximum power was 1.47 ± 0.22 and 9.59 ± 0.84 W l−1, and isometric ATPase activity was 0.034 ± 0.003 and 0.25 ± 0.01 mM s−1 in slow and in fast fibres, respectively. In fast as well as in slow fibres ATP consumption during shortening increased above isometric ATP consumption. The increase was much greater in fast fibres than in slow fibres, but became similar when expressed relative to the isometric ATPase rate. Efficiency was calculated from mechanical power and free energy change associated with ATP hydrolysis. Maximum efficiency was larger in slow than in fast fibres (0.38 ± 0.04 versus 0.28 ± 0.03) and was reached at a lower shortening velocity. Within the group of fast fibres efficiency was lower in fibres which contained more MLC3f. We conclude that both MHC and essential MLC isoforms contribute to determine efficiency of chemo‐mechanical transduction.

mentioning

confidence: 92%

Chemo‐mechanical energy transduction in relation to myosin isoform composition in skeletal muscle fibres of the rat

Reggiani

Potma²,

Bottinelli

et al. 1997

111

“…There have been many studies of the energetics of work performance by amphibian muscle but relatively few on mammalian muscle. When amphibian muscle shortens, there is a marked increase in total energy output, due to both performance of work and an increased rate of heat production (see, for example, Hill, 1938;Irving & Woledge, 1981). However, the effect of shorterning on energy liberation from mammalian muscle is less clear.…”

Section: Introductionmentioning

confidence: 98%

Energetics of fast‐ and slow‐twitch muscles of the mouse.

Barclay

Constable

Gibbs

1993

184

194

SUMMARY1. The energetic cost of work performance by mouse fast-and slow-twitch muscle was assessed by measuring the rates of thermal and mechanical energy liberation of the muscles at 21 'C. Thermal energy (heat) liberation was measured using a fastresponding thermopile.2. Bundles of muscle fibres from the slow-twitch soleus and fast-twitch extensor digitorum longus (EDL) muscles were used. Work output was controlled by performing isovelocity shortenings during the plateau of an isometric tetanus. A range of shortening velocities, spanning the possible range, was used for each muscle.3. During tetanic contractions, the rate of heat production from EDL muscle was 134-2 + 11-4 mW/g. The rate of heat production by soleus muscle was only one-fifth as great (26-8 + 2-7 mW/g).4. The maximum shortening velocity (Vmax) of EDL muscles was 2*5-fold greater than that for soleus muscles and it's force-velocity relationship was less curved. Peak power output from EDL muscles was 3-fold greater than that from soleus muscle.5. During shortening, the rate of heat output from soleus muscles increased considerably above the isometric heat rate. In contrast to soleus muscle, the rate of heat production by EDL muscle increased by only a small fraction of the isometric heat rate. The magnitude of the increases in rate was proportional to shortening velocity.6. The total rate of energy liberation (heat rate + power) by EDL muscle, shortening at 0 95 Vmax was 1-62 + 0 37 times greater than the isometric heat rate. In contrast, the rate of energy liberation from soleus muscle shortening at 0 95 Vmax was 5-21 + 0-58 times greater than its isometric heat rate. The peak mechanical efficiency (power/total energy rate) of the both muscles was approximately 30%.

“…It has been known since the work of Aubert (1956, p. 252) that shortening heat production in frog sartorius muscles is reduced at muscle lengths greater than rest length, and it has subsequently been confirmed that shortening heat and isometric tension show a similar decline with increasing length, from a sarcomere length of 2-2 um to about 2-9 #sm (Lebacq, 1972;Irving & Woledge, 1981). However, even when stretched to only 2-9 ,sm, sartorius muscles produce high resting tension and there is a large heat absorption when a resting muscle is released (Hill, 1952).…”

Section: Introductionmentioning

confidence: 99%

The variation in shortening heat with sarcomere length in frog muscle.

Homsher¹,

Irving²,

Lebacq³

1983

Self Cite

SUMMARY1. Pairs of frog semitendinosus muscles were stimulated tetanically for 2 s at 0 0C and, after 0 75 s of isometric contraction, were released at constant velocity for 0-16 s. The distance shortened was 0 3 jsm per sarcomere. The extra heat (shortening heat) associated with the release was determined by comparison with isometric control tetani.2. The mean sarcomere length at the start of stimulation was varied between 2-25 and 3-75 jsm. At the greater initial lengths there was considerable resting tension and heat was absorbed during releases of unstimulated muscles. This thermoelastic effect was also present during stimulation, so shortening heat values were calculated from the difference between the heat production ofthe stimulated and unstimulated muscle for releases over the same length range and at the same velocity.3. Laser diffraction was used to measure mean sarcomere length in the part of the muscle from which heat was recorded. At the greater initial lengths these central sarcomeres slowly elongated by a small amount during nominally isometric tetani. When a release was given during a tetanus the central sarcomere shortening was slightly less than that in a release of the unstimulated muscle with the same change of muscle length. In the period of a tetanus after the release had ended the rate of central sarcomere elongation was greater than that in an isometric tetanus.4. Shortening heat production had a large early component, during and just after the release, then continued to increase slowly up to the end of the tetanus. It is likely that sarcomere length redistribution along the muscle is responsible for the apparent slow phase, but has little effect on the early component.5. Shortening heat (determined as the early component) decreased linearly with increasing muscle length in the range studied. The intercept on the length axis was 3'78 + 0-08 ,sm per sarcomere (mean + s.E. of mean, n = 7, based on sarcomere length before stimulation). The corresponding intercept for the isometric tension before the release was 3-78+0'03 sum per sarcomere. The isometric heat rate at this time also decreased with increasing muscle length, but at 3 75 j#m per sarcomere was still 50-0 + 2-0 % of its maximum value.6. The results suggest that shortening heat, like isometric tension, is produced by the interaction of thick and thin filaments in contracting muscle.