Relationship between initial chemical reactions and oxidative recovery metabolism for single isometric contractions of frog sartorius at 0 degrees C.

1. Measurements of intitial chemical changes and recovery oxygen consumption (deltaO2) were made in unpoisoned aerobic frog sartorius muscles at 0 degrees C to provide independent measures of the chemical energy used for isometric tetani of various durations. 2. DeltaO2 was measured polarographically and increased in a curvilinear fashion with stimulus duration. For stimulations longer than 4 sec deltaO2 was a linear function of the tension‐time integral. 3. Measurements of the changes in the content of phosphorylcreatine, 'free' creatine and inorganic phosphate were made in muscles rapidly frozen during a tetanus. The average of these quantities, delta approximately P, was used to measure the initial 'high energy' phosphate utilization. No break‐down of 'high‐energy' phosphate compounds was detected up to 200 sec after relaxation of tension. Changes in the content of ATP were not observed except for a small decrease (‐0‐25+/‐0‐1 mumole/g) in muscles tetanized for 1 sec. 4. Delta approximately P also increase curvilinearly with tetanus duration and, for tetanic durations greater than 4 sec, was a linear function of the tension‐time integral. 5. Both deltaO2 and delta approximately P were quantitatively related by a constant scaling factor of about 4‐3 (delta approximately P/deltaO2) throughout the range of tetanic durations studied. The constancy of this ratio.provides evidence against the hypothesis that a significant 'missing reaction' provides energy during any one portion of the tetanus. Several hypothesis may account for the numerical value of the ration delta approximately P/deltaO2.

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