Oxygen consumption in frog sartorius muscle I. The isometric twitch
✍ Scribed by Baskin, R. J. ;Gaffin, S.
- Publisher
- Wiley (John Wiley & Sons)
- Year
- 1965
- Tongue
- English
- Weight
- 449 KB
- Volume
- 65
- Category
- Article
- ISSN
- 0095-9898
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✦ Synopsis
Direct measurements have shown that the heat output from the frog sartorius muscle stimulated under isometric conditions is maximum when the muscle is at reference length and is decreased at stretched and shortened lengths. Experiments were conducted to determine if oxygen consumption following isometric stimulation varied with length in the same manner as did heat.
A modified version of a differential volumeter was used consisting of two small sealed chambers each containing one of a pair of frog sartorius muscles. In the presence of a COZ absorbant extra oxygen consumption is indicated by movement of the index drop toward the chamber containing the stimulated muscle.
It was found that at 12°C the oxygen consumption resulting from ten isometric twitches a t reference length is 11.93 pl/g and decreases to 5.10 pl/g a t 0.75 RL and 8.64 pl/g at 1.25 RL. The absolute value of the oxygen consumption is in agreement with Hill's heat studies using appropriate heat-oxygen conversion factors. No Feng "stretch response" of a n increase in the rate of resting oxygen consumption was observed.
Measurements of developed tension were found to parallel the oxygen consumption and heat curves, being 2.28 kg/cm2 at 1.00 RL and decreasing to 1.45 kg/cm2 at 1.25 RL and approaching zero at 0.75RL.
At the shortest lengths the oxygen consumption (5.0 pl/g) is suggested to represent the equivalent of activation heat since no elastic elements were stretched. Such a suggestion is in agreement with heat studies showing that the energy of activation is approximately half of the maximum initial energy liberated in an isometric contraction.