title: Increased venous PCO2 enhances dynamic responses of avian intrapulmonary chemoreceptors.
abstract: We quantified the neural discharge of intrapulmonary chemoreceptors (IPC) innervating the left lungs of anesthetized Pekin ducks. Right and left lungs were separately unidirectionally ventilated. Alternating steps in CO2 concentration (0-6%, 11-s period) were delivered to the left lung under control conditions [mixed venous PCO2, (PVCO2) 43 +/- 4 Torr] and under venous CO2 load conditions (PVCO2 79 +/- 6 Torr). During venous CO2 loading the right lung was ventilated with 10-20% CO2, while the left lung was ventilated with a sufficient flow of gas containing 0% CO2 to maintain normal expired PCO2 (indicated by constant IPC discharge rate). Venous loading increased the peak-to-peak amplitude of the oscillation in IPC discharge by 4.3 +/- 1.8 s-1 (n = 11, P < 0.05), left lung ventilation was increased 2.6-fold, and the IPC step response became more prompt. The mean IPC discharge rate during the CO2 stepping cycle was not significantly affected (11.8 +/- 1.4 during control vs. 10.3 +/- 1.3 s-1 during venous loading). Increased IPC discharge oscillations were due to enhancement of the dynamic overshoot in receptor discharge after the 6-0% downstep in inspired CO2 and to a depression of discharge during 6% inspired CO2. We propose that the phasic enhancement of IPC discharge oscillations during venous CO2 loading may cause feedback inhibition of ventilatory drive.
authors.affiliation: Department of Medicine, University of California, San Diego, La Jolla 92093-0623.
authors.forename: S C
authors.initials: SC
authors.lastname: Hempleman
authors.forename: D E
authors.initials: DE
authors.lastname: Bebout
mesh_terms: D000280:Administration, Inhalation; D000818:Animals; D002245:Carbon Dioxide / Q000008:administration & dosage / Q000097:blood*; D002628:Chemoreceptor Cells / Q000502:physiology*; D004372:Ducks / Q000502:physiology*; D008168:Lung / Q000502:physiology*; D010313:Partial Pressure; D012016:Reference Values; D014680:Veins
chemical_list: D002245:Carbon Dioxide