Postnatal maturation of carotid body and type I cell chemoreception in therat

The site of postnatal maturation of carotid body chemoreception is unclear. To test the hypothesis that maturation occurs synchronously in type I cell s and the whale carotid body, the development of changes in the intracellul ar Ca2+ concentration responses to hypoxia, CO2, and combined challenges wa s studied with fluorescence microscopy in type I cells and compared with th e development of carotid sinus nerve (CSN) responses recorded in vitro from term fetal to 3-wk animals. Type I cell responses to all challenges increa sed between 1 and 8 days and then remained constant, with no multiplicative O-2-CO2 interaction at any age. The CSN response to hypoxia also matured b y 8 days, but CSN responses to CO2 did not change significantly with age. M ultiplicative O-2-CO2 interaction occurred in the CSN response at 2-3 wk bu t not in younger groups. We conclude that type I cell maturation underlies maturation of the CSN response to hypoxia. However, because development of responses to CO2 and combined hypoxia-CO2 challenges differed between type I cells and the CSN, responses to these stimuli must mature at other, unide ntified sites within the developing carotid body.