ATP release and metabolism by human and guinea pig airways and P2X receptor‐dependent effects on bronchopulmonary vagal afferent nerve subtypes

BACKGROUND AND PURPOSE: ATP-dependent activation of P2X receptors has been implicated in chronic cough. The mechanisms of ATP release in cough and how P2X-receptor engagement produces cough hypersensitivity are not clear. It is also unclear whether P2X receptor blockade could compromise the essential defensive functions of cough regulated by the vagal Aδ-fibres terminating in the extrapulmonary airways. EXPERIMENTAL APPROACH: We measured ATP release from isolated human and guinea pig airways. P2X receptor-dependent regulation of vagal afferent nerve discharge in vitro and respiratory reflexes in anaesthetised guinea pigs also were studied using the P2X blockers AF-353 and AF-454. KEY RESULTS: ATP was released continually and metabolised by human and guinea-pig airways. ATP release was augmented by mild mechanical stimulation (blocked by carbenoxolone) and hypotonic challenges (blocked by ruthenium red), dwarfing the ATP release evoked by acid or by TRPV4 activation. Epithelium removal prevented ATP release evoked by either mechanical stimulation of the airways or by hypotonic challenges. AF-454 inhibited α, β-methylene ATP evoked action potential discharge in bronchopulmonary nodose C-fibres, but was without effect on extrapulmonary Aδ-fibre excitability and did not prevent acid or mechanically induced cough responses evoked in anaesthetised guinea pigs. AF-454 and AF-353 did, however, inhibit α, β-methylene ATP evoked increases in airway cholinergic tone and changes in respiratory patterns, respectively. CONCLUSIONS AND IMPLICATIONS: These results predict a desirable safety profile for P2X receptor blockade and identify multiple potential biomarkers that may differentiate responders from non-responders in studies evaluating P2X blockers in chronic cough patients.