CARBON-MONOXIDE - A ROLE IN CAROTID-BODY CHEMORECEPTION

Carbon monoxide (CO), produced endogenously by heme oxygenase, has bee n implicated as a neuronal messenger. Carotid bodies are sensory organ s that regulate ventilation by responding to alterations of blood oxyg en, CO2, and pH. Changes in blood gases are sensed by glomus cells in the carotid body that synapse on afferent terminals of the carotid sin us nerve that projects to respiratory-related neurons in the brainstem . Using immunocytochemistry, we demonstrate that heme oxygenase 2 is l ocalized to glomus cells in the cat and rat carotid bodies. Physiologi cal studies show that zinc protoporphyrin IX, a potent heme oxygenase inhibitor, markedly increases carotid body sensory activity, while cop per protoporphyrin IX, which does not inhibit the enzyme, is inactive. Exogenous CO reverses the stimulatory effects of zinc protoporphyrin IX. These results suggest that glomus cells are capable of synthesizin g CO and endogenous CO appears to be a physiologic regulator of caroti d body sensory activity.