Recovery of carotid body O2 sensitivity following chronic postnatal hyperoxia in rats

Chronic postnatal hyperoxia blunts the hypoxic ventilatory response (HVR) in rats, an effect that persists for months after return to normoxia. To determine whether decreased carotid body O2 sensitivity contributes to this lasting impairment, single-unit chemoafferent nerve and glomus cell calcium responses to hypoxia were recorded from rats reared in 60% O2 through 7 d of age (P7) and then returned to normoxia. Single-unit nerve responses were attenuated by P4 and remained low through P7. After return to normoxia, hypoxic responses were partially recovered within 3 d and fully recovered within 7–8 d (i.e., at P14–15). Glomus cell calcium responses recovered with a similar time course. Hyperoxia altered carotid body mRNA expression for O2-sensitive K+ channels TASK-1, TASK-3, and BKCa, but only TASK-1 mRNA paralleled changes in chemosensitivity (i.e., downregulation by P7, partial recovery by P14). Collectively, these data do not support a role for reduced O2 sensitivity of individual chemoreceptor cells in long-lasting reduction of the HVR after developmental hyperoxia.