Oxygen consumption of skeletal muscle

Mammalian cells require a continuous supply of O 2 to carry out their functions. The O 2 pathway has an overall direction taking O 2 from the air to the mitochondria, which is a result of the mitochondrial O 2 consumption (VO 2 ). The purpose of the present study was to measure VO 2 of the rat spinotrapezius muscle in situ. The methods used provide a direct way to measure PO 2 in the interstitium and use it as an indicator of local metabolic changes. The albumin‐bound Pd‐porphyrin O 2 probe (10 mg/ml) was topically applied to both surfaces of the muscle (30 min) and allowed to diffuse into the interstitial space. A region of tissue 276 μm in diameter was excited by a flash lamp (1 Hz), and the rate of decay of the subsequent phosphorescence was used to calculate PO 2 . PO 2 was measured once per second in resting muscle before, during, and after a period of tissue compression achieved by rapid inflation of a Saran film air bag (0–120 mmHg in < 1 s), attached to a X20 objective lens. The initial PO 2 was 55.6 ± 3.6 mmHg. The critical PO 2 , at which the rate of fall of PO 2 began to deviate from linearity, was 7.5 ± 0.6 mmHg. The minimum PO 2 during flow arrest was 1.4 ± 0.1 mmHg. The rate of initial fall of PO 2 , which started immediately after the airbag inflation, was used to calculate the following VO 2 in resting muscle: 6.1 ± 0.4 ml O 2 · kg −1 · min −1 (N = 21). This method for measuring VO 2 in situ can be applied in a variety of tissues. Supported by NIH grant HL18292 .