Oxygen glomus cell

Lopez-Barneo J. 2003. Oxygen and glucose sensing by carotid body glomus cells. Curr Opin Neurobiol 13 493-499. 

A decrease below the threshold Pq, normally close to 50 Torr, in glomus cells of the carotid body or in the neonatal ductus arteriosus results in an inhibition of the tonic K current. Such oxygen-regulated inhibition of K+ channels, which may be mediated by mitochondria-derived hydrogen peroxide (Archer et al., 2004), results in an increase in cellular excitability, increased Ca + influx, and a resultant increase in the level of Ca + in the cytosol (reviewed by Lopez-Barneo et al., 1999). 

A schematic representation of how a decrease in oxygen tension (hypoxia) may affect carotid body glomus cell function. In the mitochondrial model, hypoxia affects either reactive oxygen species (ROS) production or ATP production of mitochondria. Both of these may affect the outward flux of potassium via the potassium channel with the downstream effects shown in the diagram. In the membrane model, the ROS production by membrane-bound molecules (cytochromes) is oxygen sensitive, and thereby affected by hypoxia. Thus, these membrane-bound molecules function as proximal oxygen sensors and cause effects on potassium channels with the downstream effects described in the figure and in the text... 

Hypoxia-induced neurosecretion firom glomus cells is mediated by a rise in intracellular calcium, which resembles the CSN activity response to hypoxia in its hyperbolic shape (37,44,68), PO2 range, and relationship to neurosecretion (69,70). Because neurosecretion and (presumably) afferent nerve activity depend on the type I cell [Ca ]i response to hypoxia, age-related changes in this crucial transduction step could account for maturation of O2 sensitivity. The original hypothesis of the first studies in this area was simply that a major site of chemoreceptor resetting and development of oxygen sensitivity, within the carotid body, lies in the type I cell. 

Montoro RJ, Urena J, Femandez-Chacon R, Alvarez dX, Lopez-Bameo J. Oxygen sensing by ion channels and chemotransduction in single glomus cells. J Gen Physiol 1996 107(1) 133-143. 

IV. Glomus Cells Are Combined Glucose and Oxygen Sensors... 

The above seminal studies gave a preponderant role to glomus cells as intermediary elements between what is sensed (chemicals in the blood) and how neural information is generated. But, the need to count on glomus cells for the transduction of chemical stimuli into nerve impulses has been subjected to much debate and it is stiU an open problem. In a book devoted to oxygen sensing, this subject deserves a closer examination. 

In conclusion, the distribution of NOS immunoreactivity and the pharmacological and physiological evidence analyzed and discussed here support the proposal that CB endogenous NO exerts a tonic inhibitory effect on CB chemoreception. Clearly, NO in low concentration is a broad inhibitory modulator of the chemoreception process in the CB. NO may modulate chemoreception by regulating the CB vascular tone, the oxygen delivery to the chemoreceptor cells, and the excitability of glomus cells and petrosal sensory neurons. 

HO is also present in the carotid body in the oxygen-sensing glomus cells and inhibition of HO with metalloporphyrins markedly alters the afferent activity of the carotid body (95). 

Eyzaguirre C. Electrical coupling between glomus cells and nerve terminals. In Lahiri S, Prabhakar NR, Foster RE, eds. Oxygen Sensing Molecule to Man. London Plenum, 2000 349-357. 

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