The metabolism of phosphocreatine during an isometric tetanus in the frog sartorius muscle

Abstract

1. 1. A study was made of the phosphocreatine breakdown in anaerobic iodoacetate-poisoned muscle associated with one or several isometric tetani at o°. 2. 2. The rate of phosphocreatine breakdown in the course of tetanization, apart from the earliest moments, was 0.28 μmole/g/sec. This was constant for up to 60 sec until the near-exhaustion of all phosphocreatine, although the tension decreased by 0.89% per sec, and was not affected by dividing the period of stimulation into several separate tetani. 3. 3. This rate of phosphocreatine breakdown is consistent with known values of the maintenance heat if the apparent enthalpy change for phosphocreatine hydrolysis and associated ionization changes amounts to —10 000 cal/mole. 4. 4. An extra-metabolism was found which was proportional to the number of tetani and not to their durations, and which averaged 0.33 μmole/g/tetanus. 5. 5. A small part of this extra-metabolism is due to elastic work and internal shortening during tension generation, and a larger part may represent the residual activation heat during relaxation. The remainder appears insufficient to account for the “labile part” of the maintenance heat, at the present state of knowledge. However, several aspects of this problem require further examination.