Oxygen dependence of respiratory rate (VO2) in rat spinotrapezius muscle in situ measured with phosphorescence quenching microscopy (PQM)

Abstract

ObjectiveThe sensitivity of isolated cells to PO2 is described by Hill's equation with a low Km (< 5 torr). Cells in intact tissues are more sensitive to O2 deficiency. To study the oxygen dependence of VO2 in muscle fibers we developed a method to register and interpret O2 disappearance curves (ODC).MethodWe employed PQM using a probe distributed in the interstitium. Rapid pressure onset to the tissue extruded most of the RBCs from the muscle vessels making the ODC independent of hemoglobin. The contribution to the O2 consumption by PQM was evaluated and accounted for. The corrected ODC was converted into the PO2 dependence of VO2. Fitting equations obtained from a model of heterogeneous PO2 distribution was applied to recover the parameters of respiration in muscle fibers.ResultsIn 6 muscles the rate of O2 consumption at rest was Vmax = 139 ± 6 nl O2/cm3•s, Km = 12 ± 2 torr and the correlation between them was 0.94. The PO2 drop across a fiber was Ä = 4.1 to 4.9 torr. Critical PO2 was estimated as 22 torr at VO2 = 90 nl O2/cm3•s.ConclusionThe oxygen dependence of respiration can be measured in thin muscles under different experimental conditions. In resting muscle Km and critical PO2 are substantially lower than interstitial PO2 = 51 ± 3 torr, a result discordant with the hypothesis of metabolic regulation of oxygen supply to tissue. The PO2 gradient across a muscle fiber was found to be small.Support: NIH grant R01HL18292