Comparison of intrapulmonary chemoreceptor response to P_CO2 in the duck and chicken

Intrapulmonary chemoreceptors (IPC) in the burrowing owl are reported to be much less sensitive to P_CO2 than IPC in the chicken. This blunted IPC sensitivity has been suggested to be a physiological adaptation to hypercapnic subterrranean environments. To investigate the natural variation IPC responses in non-burrowing species, stimulus-response characteristics of 87 IPC in 22 anesthetized Pekin ducks were recorded and compared to those from 54 previously reported chicken IPC. Average logarithmic stimulus response curves were described by slopes of -11.2 and -10.7 imp·(sec·InP_CO2)^-1 for duck and chicken, respectively. Each had slopes steeper than the -6.87 imp· (sec·InP_CO2)^-1 slope reported for the burrowing owl. As with chicken IPC, slopes and intercepts of the individual curves were highly correlated in the duck. It appears that a general mechanism of receptor transduction exists in birds, with some quantitative interspecies variation.