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Query: UMLS:C0020440 (hypercapnia)
 7,939 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Breathing was monitored during normocarbia, hypercarbia (6% CO2 in air), and the period immediately after the return to normocarbic conditions in intact, olfactory-denervated, and vagotomized bullfrogs. In intact frogs, ventilation increased during hypercarbia, but the breathing pattern remained episodic. Immediately upon return to air, there was a further paradoxical increase in breathing frequency, and breathing became continuous in most frogs. Results obtained from animals after olfactory receptor denervation indicate that tonic stimulation of olfactory receptors by airway CO2 inhibited breathing during hypercarbia. Measurements of the kinetics of changes in airway and arterial blood CO2 levels support the suggestion that the sudden release of this inhibition on the return to normocarbic conditions was responsible for the posthypercarbic hyperpnea. Vagotomy increased ventilation during normocarbia. Hypercarbia now caused a change in breathing pattern but had no net effect on total ventilation, suggesting that pulmonary vagal feedback inhibited ventilation during normocarbia but stimulated ventilation during hypercarbia. Although olfactory and pulmonary receptor feed-back shape the breathing pattern, they were not responsible for initiating or terminating the episodes of breathing.
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PMID:CO2-sensitive olfactory and pulmonary receptor modulation of episodic breathing in bullfrogs. 876 95

Animals have evolved homeostatic responses to changes in oxygen availability that act on different timescales. Although the hypoxia-inducible factor (HIF) transcriptional pathway that controls long-term responses to low oxygen (hypoxia) has been established, the pathway that mediates acute responses to hypoxia in mammals is not well understood. Here we show that the olfactory receptor gene Olfr78 is highly and selectively expressed in oxygen-sensitive glomus cells of the carotid body, a chemosensory organ at the carotid artery bifurcation that monitors blood oxygen and stimulates breathing within seconds when oxygen declines. Olfr78 mutants fail to increase ventilation in hypoxia but respond normally to hypercapnia. Glomus cells are present in normal numbers and appear structurally intact, but hypoxia-induced carotid body activity is diminished. Lactate, a metabolite that rapidly accumulates in hypoxia and induces hyperventilation, activates Olfr78 in heterologous expression experiments, induces calcium transients in glomus cells, and stimulates carotid sinus nerve activity through Olfr78. We propose that, in addition to its role in olfaction, Olfr78 acts as a hypoxia sensor in the breathing circuit by sensing lactate produced when oxygen levels decline.
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PMID:Oxygen regulation of breathing through an olfactory receptor activated by lactate. 2656 Mar 2