Abstract

Protective roles for protease-activated receptor-2 (PAR₂) in the airways including activation of epithelial chloride (Cl^–) secretion are based on the use of presumably PAR₂-selective peptide agonists. To determine whether PAR₂ peptide-activated Cl^– secretion from mouse tracheal epithelium is dependent on PAR₂, changes in ion conductance across the epithelium [short-circuit current (I_SC)] to PAR₂ peptides were measured in Ussing chambers under voltage clamp. In addition, epithelium- and endothelium-dependent relaxations to these peptides were measured in two established PAR₂ bioassays, isolated ring segments of mouse trachea and rat thoracic aorta, respectively. Apical application of the PAR₂ peptide SLIGRL caused increases in I_SC, which were inhibited by three structurally different neurokinin receptor-1 (NK₁R) antagonists and inhibitors of Cl^– channels but not by capsaicin, the calcitonin gene-related peptide (CGRP) receptor antagonist CGRP_8–37, or the nonselective cyclooxygenase inhibitor indomethacin. Only high concentrations of trypsin caused an increase in I_SC but did not affect the responses to SLIGRL. Relaxations to SLIGRL in the trachea and aorta were unaffected by the NK₁R antagonist nolpitantium (SR 140333) but were abolished by trypsin desensitization. The rank order of potency for a range of peptides in the trachea I_SC assay was 2-furoyl-LIGRL > SLCGRL > SLIGRL = SLIGRT > LSIGRL compared with 2-furoyl-LIGRL > SLIGRL > SLIGRT > SLCGRL (LSIGRL inactive) in the aorta relaxation assay. In the mouse trachea, PAR₂ peptides activate both epithelial NK₁R coupled to Cl^– secretion and PAR₂ coupled to prostaglandin E₂-mediated smooth muscle relaxation. Such a potential lack of specificity of these commonly used peptides needs to be considered when roles for PAR₂ in airway function in health and disease are determined.