Hypoxia induces production of nitric oxide and reactive oxygen species in glomus cells of rat carotid body

The carotid body is an arterial chemoreceptor organ that senses arterial pO₂ and pH. Previous studies have indicated that both reactive oxygen species (ROS) and nitric oxide (NO) are important potential mediators that may be involved in the response of the carotid body to hypoxia. However, whether their production by the chemosensitive elements of the carotid body is indeed oxygen-dependent is currently unclear. Thus, we have investigated their production under normoxic (20% O₂) and hypoxic (1% O₂) conditions in slice preparations of the rat carotid body by using fluorescent indicators and confocal microscopy. NO-synthesizing enzymes were identified by immunohistochemistry and histochemistry, and the subcellular localization of the NO-sensitive indicator diaminofluorescein was determined by a photoconversion technique and electron microscopy. Glomus cells of the carotid body responded to hypoxia by increases in both ROS and NO production. The hypoxia-induced increase in NO generation required (to a large extent, but not completely) extracellular calcium. Glomus cells were immunoreactive to endothelial NO synthase but not to the neuronal or inducible isoforms. Ultrastructurally, the NO-sensitive indicator was observed in mitochondrial membranes after exposure to hypoxia. The data show that glomus cells respond to exposure to hypoxia by the enhanced production of both ROS and NO. NO production by glomus cells is probably mediated by endothelial NO synthase, which is activated by calcium influx. The presence of NO indicator in mitochondria suggests the hypoxic regulation of mitochondrial function via NO in glomus cells.