Effect of initial length on relations between oxygen uptake and load in dog muscle

1976 ◽  
Vol 230 (4) ◽  
pp. 1008-1012 ◽  
Author(s):  
WN Stainsby ◽  
JK Barclay
Keyword(s):  
Skeletal Muscle ◽  
Oxygen Uptake ◽  
The Other ◽  
Mammalian Skeletal Muscle ◽  
Initial Length ◽  
Muscle Preparation ◽  
Optimal Length ◽  
Muscle Energetics ◽  
Isotonic Contractions ◽  
Fenn Effect

Oxygen uptake for brief tetanic contractions was calculated from measurements of blood flow and blood arteriovenous oxygen content differences. Each muscle preparation was pretested under isometric conditions to establish optimal length, Lo. After this one group of preparations performed afterload isotonic contractions at several loads with initial length, Li, less than Lo. The other groups of preparations performed similar contractions with Li greater than Lo. When Li was less than Lo, oxygen uptake for the highest load was always greater than oxygen uptake at the lowest load whereas intermediate loads were usually higher than both extremes. However, when Li was greater than Lo, oxygen uptake at the highest load was always less than oxygen uptake at the lowest load; again the intermediate loads were usually higher than both extremes. The data confirm and extend similar effects of initial length on heat production for contractions by amphibian muscles (7). It seems likely that the differences in initial lengths may account for the fact that the Fenn effect has not previously been observed in studies of mammalian skeletal muscle energetics.

Length dependence of staircase potentiation: interactions with caffeine and dantrolene sodium

2000 ◽  
Vol 78 (4) ◽  
pp. 350-357 ◽  
Author(s):  
Dilson E Rassier ◽  
Brian R MacIntosh
Keyword(s):  
Skeletal Muscle ◽  
Gastrocnemius Muscle ◽  
Repetitive Stimulation ◽  
Mammalian Skeletal Muscle ◽  
Optimal Length ◽  
Dantrolene Sodium ◽  
Length Dependence ◽  
Before And After ◽  
Isometric Twitch

In skeletal muscle, there is a length dependence of staircase potentiation for which the mechanism is unclear. In this study we tested the hypothesis that abolition of this length dependence by caffeine is effected by a mechanism independent of enhanced Ca2+ release. To test this hypothesis we have used caffeine, which abolishes length dependence of potentiation, and dantrolene sodium, which inhibits Ca2+ release. In situ isometric twitch contractions of rat gastrocnemius muscle before and after 20 s of repetitive stimulation at 5 Hz were analyzed at optimal length (Lo), Lo - 10%, and Lo + 10%. Potentiation was observed to be length dependent, with an increase in developed tension (DT) of 78 ± 12, 51 ± 5, and 34 ± 9% (mean ± SEM), at Lo - 10%, Lo, and Lo + 10%, respectively. Caffeine diminished the length dependence of activation and suppressed the length dependence of staircase potentiation, giving increases in DT of 65±13, 53 ± 11, and 45 ± 12% for Lo - 10%, Lo, and Lo + 10%, respectively. Dantrolene administered after caffeine did not reverse this effect. Dantrolene alone depressed the potentiation response, but did not affect the length dependence of staircase potentiation, with increases in DT of 58 ± 17, 26 ± 8, and 18 ± 7%, respectively. This study confirms that there is a length dependence of staircase potentiation in mammalian skeletal muscle which is suppressed by caffeine. Since dantrolene did not alter this suppression of the length dependence of potentiation by caffeine, it is apparently not directly modulated by Ca2+ availability in the myoplasm.

Length-dependent potentiation and myosin light chain phosphorylation in rat gastrocnemius muscle

1997 ◽  
Vol 273 (1) ◽  
pp. C198-C204 ◽  
Author(s):  
D. E. Rassier ◽  
L. A. Tubman ◽  
B. R. MacIntosh
Keyword(s):  
Skeletal Muscle ◽  
Gastrocnemius Muscle ◽  
Average Rate ◽  
Muscle Length ◽  
Repetitive Stimulation ◽  
Mammalian Skeletal Muscle ◽  
Optimal Length ◽  
Regulatory Light Chains ◽  
Dependent Change

Changes in muscle length affect the degree of staircase potentiation in skeletal muscle, but the mechanism by which this occurs is unknown. In this study, we tested the hypothesis that length-dependent change in staircase is modulated by phosphorylation of the myosin regulatory light chains (RLC), since this is believed to be the main mechanism of potentiation. In situ isometric contractile responses of rat gastrocnemius muscle during 10 s of repetitive stimulation at 10 Hz were analyzed at optimal length (Lo), Lo - 10%, and Lo + 10%. The degree of enhancement of developed tension during 10 s of repetitive stimulation was observed to be length dependent, with increases of 118.5 +/- 7.8, 63.1 +/- 3.9, and 45.6 +/- 4.1% (means +/- SE) at Lo - 10%, Lo, and Lo + 10%, respectively. Staircase was accompanied by increases in the average rate of force development of 105.6 +/- 7.7, 55.6 +/- 4.1, and 37.2 +/- 4.4% for Lo - 10%, Lo, and Lo + 10%, respectively. RLC phosphorylation after 10 s of 10-Hz stimulation was higher than under resting conditions but not different among Lo - 10% (40 +/- 3.5%), Lo (35 +/- 3.5%), and Lo + 10% (41 +/- 3.5%). This study shows that there is a length dependence of staircase potentiation in mammalian skeletal muscle that may not be directly modulated by RLC phosphorylation. Interaction of RLC phosphorylation with length-dependent changes in Ca2+ release and intermyofilament spacing may explain these observations.

Release of Intracellular Enzymes from An Isolated Mammalian Skeletal Muscle Preparation

1983 ◽  
Vol 65 (2) ◽  
pp. 193-201 ◽  
Author(s):  
D. A. Jones ◽  
M. J. Jackson ◽  
R. H. T. Edwards
Keyword(s):  
Skeletal Muscle ◽  
Contractile Activity ◽  
Atp Depletion ◽  
Mammalian Skeletal Muscle ◽  
Enzyme Release ◽  
Muscle Preparation ◽  
Muscle Enzymes ◽  
Hypoxic Conditions ◽  
Detergent Treatment

1. An isolated skeletal muscle preparation is described which has been used to study the efflux of enzymes in response to contractile activity, metabolic poisons and detergent treatment. 2. In both fast and slow muscles contractile activity caused a release of lactate dehydrogenase and creatine kinase that reached a peak 1–2 h after the end of stimulation. There was very little release during the 30 min stimulation period whether the muscles were under aerobic or hypoxic conditions. 3. Incubation of the muscles with cyanide and iodoacetate caused a similar delayed release of enzyme. 4. Disruption of cell membranes with detergent treatment caused an entirely different and very rapid pattern of enzyme release. 5. Enzyme release from the fatigued isolated muscle preparations appears to be initiated as a consequence of phosphorylcreatine or ATP depletion. The relevance of this to release of muscle enzymes after activity in vivo is discussed.

scholarly journals The Dynamic Properties of Mammalian Skeletal Muscle

1968 ◽  
Vol 51 (3) ◽  
pp. 369-384 ◽  
Author(s):  
Alan S. Bahler ◽  
John T. Fales ◽  
Kenneth L. Zierler
Keyword(s):  
Skeletal Muscle ◽  
Phase Space ◽  
Dynamic Properties ◽  
Mammalian Skeletal Muscle ◽  
Initial Length ◽  
Ordinary Sense ◽  
Shortening Velocity ◽  
Velocity Of Shortening ◽  
Force Velocity ◽  
Elastic Elements

The dynamic characteristics of the rat gracilis anticus muscle at 17.5°C have been determined by isotonic and isometric loading. For a fixed initial length these characteristics were represented either as a family of length-velocity phase trajectories at various isotonic afterloads or as a series of force-velocity curves at different lengths. An alternate method of viewing these data, the length-external load-velocity phase space, was also generated. When the muscle was allowed to shorten from different initial lengths, the velocity of shortening achieved at a given length was lower for longer initial lengths. The amount of departure was also dependent upon the isotonic load, the greater the load the greater the departure. The departures were not caused by changes in the elastic elements of the muscle or fatigue in the ordinary sense. When the behavior of the muscle was investigated at different frequencies of stimulation, the shortening velocity was a function of the number of stimulating pulses received by the muscle at a given frequency. The shortening velocity of the rat gracilis anticus muscle is, therefore, not only a function of load and length, but also of an additional variable related to the time elapsed from onset of stimulation.

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