THE MEANING OF H2O2 GENERATION IN CAROTID-BODY CELLS FOR PO2 CHEMORECEPTION

The rat carotid body is able to generate H2O2 in type-I cells with the aid of an electron-transferring chain with cytochrome b as the major component as it can be detected by spectrophotometry as well is confocal laser-microscopy. This cytochrome b is reducible by hypoxia, but not by cyanide, indicating that it does not participate in the energy production by the respiratory chain. The carotid body possesses a glutathione peroxidase (GPO) which scavenges H2O2 and other organic hydroperoxides. The nervous chemoreceptor discharge can be inhibited by external application of hydroperoxides with a similar half maximal value (60-80 muM) as used to stimulate GPO. A hypothetical signal chain is described which suggests the involvement of cytochrome b as an O2 sensor in PO2 chemoreception of the carotid body and the degradation of H2O2 by glutathione to control the K+-conductivity of carotid body cells.