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

Oxygen consumption following isometric tetanic contractions of single fibres and multifibre preparations of the tibialis anterior muscle of Rana temporaria was determined by continuous polarographic measurement of the PO2 in a 280 microliter 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 oxygen-measuring system were assessed by injection of 1.6 microliter dye into the chamber and filming its subsequent distribution, and by injection of 1.6 microliter Ringer solution with a high (or low) oxygen content into the chamber and measuring the subsequent change of oxygen. It was found that a change in oxygen was measured after a true delay of 3 s and with an over-all time constant of 3.25 s following that delay. For seven single fibres the oxygen consumption following a 3 s tetanus was on average 2.46 mumol g-1; the average integrated value of the developed stress was 0.98 N mm-2 s. These two values were on average about 45% lower for the same tetani of multifibre preparations, but the average ratio of oxygen consumption to integrated stress was the same. Oxygen consumption was varied by changing tetanus duration. When the amount of oxygen consumed was plotted against stress integral a non-linear relationship was found because oxygen consumption increased less than the integrated stress value with longer tetani. Oxygen 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 oxygen consumed. The finding that oxygen 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 oxygen consumption on tetanus duration, as reported in the literature for frog muscle at 0 degree C, was not found.