Optical measurement of perfused rat hindlimb muscle with relation of the oxygen metabolism.

Optical measurements of myoglobin (Mb) and cytochromes (Cyts) in the isolated rat hindlimb muscle perfused with cell-free medium were performed at 35 and 15 degrees C under various oxygen supply, in the relation to the oxygen metabolism. Molar ratio of Cyt a + a3, Cyt b, Cyt c + c1, and Mb, oxygen affinity of Mb (P50), and the thermodynamic parameter (delta H degree) of Mb oxygenation in cyanide-perfused muscle were similar to those reported. The "apparent P50" of Mb in cyanide-free muscle was almost two orders larger in magnitude than P50 in the presence of cyanide. O2 uptake by the perfused hindlimb muscle was constant above O2 supply of 0.73 mumol/(min.g muscle) (under a flow rate of 1.0 ml/(min.g muscle) at 35 degrees C). Below the value of O2 supply, the O2 uptake decreased and lactate/pyruvate ratio increased. The critical mean oxygen tension in tissue (estimated by Mb oxygenation) for O2 uptake at 35 degrees C was ca. 10 mmHg. It was found that oxidation level (%) of Cyt a + a3 was equivalent to oxygenation level (%) of Mb at 35 degrees C, while the oxidation level of Cyt a + a3 was higher than the oxygenation level of Mb at 15 degrees C. Based on the results, the uneven distribution of O2 in the muscle tissue and the intracellular O2 gradient were discussed.