OXYGEN SENSING BY GLOMUS [TYPE 1] CELL

Current Theories Regarding The Mechanism Of Oxygen Sensing By The Glomus [ Type 1] Cell In The Cartoid Body

Current Theories Regarding The Mechanism Of Oxygen Sensing By The Glomus [ Type 1] Cell In The Cartoid Body

Carotid bodies are sensory organs that detect changes in arterial blood oxygen, and the ensuing reflexes are critical for maintaining homeostasis during hypoxemia. During the past decade, tremendous progress has been made toward understanding the cellular mechanisms underlying oxygen sensing at the carotid body.

Molecular oxygen is an essential substrate for many biochemical reactions, including those involved in energy production. Oxygen binds to heme with high affinity, and several biologically important enzymes, especially those associated with mitochondrial respiration (such as cytochromes), contain heme. According to this idea, the oxygen-sensing process involves mitochondria in glomus cells and a cytochrome with an unusually low affinity for oxygen serves as the oxygen sensor. In support of the mitochondrial hypothesis, Biscoe et al. reported that hypoxia causes mitochondrial depolarization in glomus cells. (Zhong 1997 599-612) More importantly, hypoxia-induced mitochondrial depolarization in glomus cells occurred at much higher PO 2 values compared with depolarization of mitochondria in neurons of the dorsal root ganglion. These observations indicate that mitochondria in glomus cells are sensitive to modest changes in oxygen compared with other neuronal cells. It has been repeatedly demonstrated that substances such as cyanide, which inhibit mitochondrial respiration, mimic the effects of hypoxia on sensory discharge. Specific inhibitors of mitochondrial respiration (e.g., antimycin A) also augment the basal sensory activity and prevent the sensory response to hypoxia but not to CO2. More recent studies have shown that high concentrations of CO augment sensory discharge in a reversible manner similar to hypoxia. The stimulatory effect of CO seems to coincide with inhibition of cytochrome(s) presumably of mitochondrial origin, as ...