O2 microelectrode studies were conducted in the cat carotid body (CB) to investigate the hypothesis that there is a second, low affinity metabolic pathway for O2 in addition to classical oxidative metabolism. Tissue PO2 (PtiO2) and O2 disappearance rates (dPO2/dt) after brief blood flow occlusion were measured with recessed cathode microelectrodes (tip diameter less than 5 microns) at 150 sites in 15 normal cats (controls) and at 154 sites in 5 cats in which one CB had been denervated 2 or 3 days before the experiments. Mean PtiO2 was slightly higher in denervated CBs: 79.6 +/- 1.6 (SE) Torr compared with 76.4 +/- 2.0 Torr for controls (P = not significant). Mean dPO2/dt was 8.4% faster: -8.42 +/- 0.28 Torr/s compared with -7.77 +/- 0.43 Torr/s for controls (P less than 0.05). The O2 consumption rate (VO2), calculated from dPO2/dt correcting for cat oxyhemoglobin, was 7.5% higher: 1.62 and 1.51 ml.100 g-1.min-1, respectively, for denervated and control CBs (P less than 0.05). The apparent Michaelis-Menten constant, Kmapp (defined as the PtiO2 where dPO2/dt decreased by 50% from the initial rate during the first 3 s after occlusion) was determined for each O2 disappearance curve. After denervation, Kmapp decreased significantly by -47%: 12.0 +/- 1.3 Torr compared with 22.6 +/- 2.5 Torr for controls (P less than 0.01). The data provide evidence for a second metabolic pathway for O2 in the CB that loses its influence on VO2 after denervation.
- Copyright © 1989 the American Physiological Society