Oxygen uptake of frog skeletal muscle fibres following tetanic contractions at 18 degrees C.

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Abstract
O2 consumption following isometric tetanic contractions of single fibers and multifiber preparations of the tibialis anterior muscle of R. temporaria was determined by continuous polarographic measurement of the PO2 in a 280 .mu.l glass chamber. Mixing of the fluid surrounding the muscle was achieved by an Archimedian screw. Force was measured via a stainless-steel wire leaving the chamber via a glass capillary. The characteristics of the O2-measuring system were assessed by injection of 1.6 .mu.l dye into the chamber and filming its subsequent distribution and by injection of 1.6 .mu.l Ringer solution with a high (or low) O2 content into the chamber and measuring the subsequent change of O2. It was found that a change in O2 was measured after a true delay of 3 s and with an over-all time constant of 3.25 s following that delay. For 7 single fibers the O2 consumption following a 3 s tetanus was on average 2.46 .mu.mol g-1; the average integrated value of the developed stress was 0.98 N mm-2 s. These 2 values were on average about 45% lower for the same tetani of multifiber preparations, but the average ratio of O2 consumption to integrated stress was the same. O2 consumption was varied by changing tetanus duration. When the amount of O2 consumed was plotted against stress integral a non-linear relationship was found because O2 consumption increased less than the integrated stress value with longer tetani. O2 consumption did not start at the onset of contraction but about 10 s later. It then followed an exponential time course with an average time constant of 120 s. Delay and time constant were independent of the amount of O2 consumed. The finding that O2 consumption follows contraction after a delay of a few seconds confirms a similar conclusion drawn indirectly from studies on recovery heat by other investigators. A dependency of the time course of O2 consumption on tetanus duration, as reported in the literature for frog muscle at 0.degree. C, was not found.