Study of CO2 sensitive vagal afferents in the cat lung

Single unit activity was recorded in the cat vagus in order to detect possible receptors firing in response to changing lung CO2 concentration. The cats were ventilated at a high rate (60-120 breaths per min) and inspired CO2 concentration was altered between 0 and 8% in a step-like fashion, each phase consisting of about 10 breaths. Thus the effects of changing intrapulmonary CO2 concentration could be differentiated from the effects of stretch of lung tissue. Activity was recorded in 7 cats from 120 units firing in phase with ventilation. Many receptors showed some CO2 sensitivity, but no fiber was found discharging in response to CO2 exclusively. The results provide no evidence for the occurence of specific CO2 receptors in the feline lung with vagal afferents functionally similar to those reported for the avian lung.