Simultaneous Measurement of Cytochrome a₃ Reduction and Chemoreceptor Afferent Activity in the Carotid Body

Abstract

THE discharge frequency of carotid body chemoreceptors increases progressively as p_aO₂ is reduced below 250–150 mm Hg¹. Chemical agents which either inhibit electron transport or uncouple oxidative phosphorylation in other tissues also increase chemoreceptor discharge^2,3; however, the fall in pO₂ required to stimulate the receptors physiologically is much smaller than that required to influence mitochondrial respiration in other tissues^4,5. It appears then that mitochondria of the carotid chemoreceptors must have unusual properties if they play a part in the oxygen related generation of chemoreceptor impulses. To evaluate the relationship between chemoreceptor discharge and respiratory chain activity we simultaneously measured the frequency of the potentials and the cytochrome a₃ reduction level in the carotid body. The organ was perfused with physiological saline in vitro because it must be both adequately oxygenated and free of haemoglobin to permit spectrophotometric measurement of cytochrome a₃ reduction.