Profiles for ATP and Adenosine Release at the Carotid Body in Response to O₂ Concentrations

Abstract

Excitatory effects on carotid body (CB) chemotransduction have been described for both adenosine and ATP. Adenosine when applied exogenously increases carotid sinus nerve (CSN) discharges in the cat, in vivo (McQueen and Ribeiro, 1983) and in vivo (Runold et al., 1990). Administration of adenosine and drugs that increase its endogenous levels stimulate ventilation in rats, an effect abolished by the section of CSN and mediated by A₂ receptors (Monteiro and Ribeiro, 1987, 1989; Ribeiro and Monteiro, 1991). In humans, the intravenous infusion of adenosine causes hyperventilation and dyspnoea, an effect attributed to the activation of CB (Watt and Routledge, 1985, Watt et al., 1987; Maxwell et al., 1986; 1987, Uematsu et al., 2000). The excitatory effect of ATP at the CB described by Zhang et al. (2000) in co-cultures of type I cells with petrosal neurons was further supported by the finding that mice deficient in P2X₂ showed a markedly attenuated ventilatory response to hypoxia (Rong et al., 2003) and by the detection of hypoxia- evoked ATP release from chemoreceptor cells of the rat carotid body (Buttigieg and Nurse, 2004).