Stimulus Interaction in the Responses of Carotid Body Chemoreceptor Single Afferent Fibers

The characteristics of steady-state responses of single afferent fibers of carotid chemoreceptors to independent changes in arterial Po2, and Pco2 were investigated in cats. The arterial blood pressure was maintained within the normal limits (115-130 torr). Single chemoreceptor afferent fibers responded to changes both in arterial Po2 and Pco2. The relationship between the activity of chemoreceptors and changes in arterial Pco2 was linear at a constant arterial Po2. The two stimuli showed multiplicative interaction. The activity approached zero (threshold) as arterial Pco2 was decreased at a constant arterial Po2; a decrease in arterial Po2 decreased the arterial Pco2 threshold. These response characteristics of a single fiber suggest that the sensory receptor may be activated through a single mechanism by the two stimuli. The data fit into an idea that the mechanism may involve a conformational change in the membrane-bound polymeric chromophore group which reacts with O2 reversibly and shows a Bohr-shift.