Chemical energetics in repeated contractions of frog sartorius muscles at 0 degrees C.

1. Recovery oxygen consumption (DeltaO(2)) was measured in aerobic, unpoisoned frog sartorius muscles at 0 degrees C following a series of repeated tetani.2. For a series of tetani having nearly identical tension-time integrals, DeltaO(2) was dependent on the interval between tetani and reached a maximal value for intervals equal to or greater than 200 sec.3. For a series of tetani at short (5 sec) intervals, DeltaO(2) was not distinguishable from DeltaO(2) following a single long tetanus having a tension-time integral similar to that of the sum of the series.4. A model is proposed to account for these observations in terms of the initial chemical reactions (Delta approximately P) including a saturable non-steady state reaction which utilizes about 1 mumole Delta approximately P/g and which is superimposed on an energy utilization proportional to the tension-time integral. Measurements of DeltaO(2) and Delta approximately P as functions of tetanic duration and interval between tetani are consistent with such a model.5. These experiments show that, in addition to parameters usually considered, the previous contractile history of a muscle plays a significant role in determining the chemical energy cost of an isometric contraction.