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 paO2 is reduced below 250–150 mm Hg1. Chemical agents which either inhibit electron transport or uncouple oxidative phosphorylation in other tissues also increase chemoreceptor discharge2,3; however, the fall in pO2 required to stimulate the receptors physiologically is much smaller than that required to influence mitochondrial respiration in other tissues4,5. 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.