Purinergic mechanisms in breathing control

[Objectives]: Carotid body (CB) chemoreceptor cells are PO2, PCO2/pH sensors-efectors which upon a decrease in PO2 or a PCO2/[H+] increase, release neurotransmitters that regulate the firing rate in the sensory fibres of the carotid sinus nerve (CSN). CSN terminate in the brainstem, where the information it coveys is integrated to generate compensatory ventilatory responses aimed to normalize blood gases. The chemoreceptor cells possess a wide array of neurotransmitters, whose relative significance in the genesis of conducted activity in the CSN is unknown. Present study, carried out in young adult rats, aimed to define the significance of adenosine and ATP to generate conducted action potentials in the CSN at different intensities of hypoxia. [Materials]: To ascertain their significance we have measured: a) adenosine and ATP receptors in the somas of the CSN sensory neurons; b) metabolic profile of adenosine and ATP in chemoreceptor cells and their rate of release at several PO2 levels, c) effect of selective adenosine and ATP antagonists on the firing frequencies recorded in the CSN; d) effect of adenosine and ATP antagonists on ventilation at different ischemic hypoxic intensities; e) some additional data on aged animals and in animals exposed to chronic sustained hypoxia (CSH) would also be presented. [Results]: Findings indicate that adenosine and ATP are the main players of the hypoxic chemotransmission in the CB sensory synapse. Adenosine is more relevant during mild hypoxia while ATP is prime during intense hypoxia. This relative contribution is maintained in aging, although overall CB drive lessens. In CSH the role of adenosine in fixing CSN responses and ventilation to acute hypoxic tests seems maintained, but ATP function seems to decrease. [Conclusions]: In the presentation of our data we shall also provide some information on the functional significance of adenosine and ATP on the central control of breathing.