Developmental aspects of oxygen sensing by the carotid body.

The carotid body chemoreceptors, the major hypoxia sensory organs for the respiratory system, undergo a significant increase in their hypoxia responsiveness in the postnatal period. This is manifest by a higher level of afferent nerve activity for a given level of arterial oxygen tension. The mechanism for the enhanced sensitivity is unresolved, but most work has focused on the glomus cell, a secretory cell apposed to the afferent nerve ending and believed to be the site of hypoxia transduction. The glomus cell secretory response to hypoxia increases postnatally, and this is correlated with an enhanced calcium rise in response to hypoxia and an increase in oxygen-sensitive potassium currents. These changes are sensitive to the level of hypoxia in the postnatal period, and significant impairment of organ function is observed with postnatal hypoxia as well as postnatal hyperoxia. Although many questions remain, especially with regard to the coupling of glomus cells to nerve endings, the use of cellular and molecular techniques should offer resolution in the near future.