Effect of protease-activated receptor 2 activation on single TRPV1 channel activities in rat vagal pulmonary sensory neurons

Protease-activated receptor 2 (PAR(2)) is involved in airway inflammation and airway hyperresponsiveness; both are the prominent features of asthma. Transient receptor potential vanilloid receptor 1 (TRPV1) is expressed in pulmonary sensory nerves, functions as a thermal and chemical transducer and contributes to neurogenic inflammation. Using cell-attached single-channel recordings we investigated the effect of PAR(2) activation on single TRPV1 channel activities in isolated pulmonary sensory neurons. Our immunohistochemical study demonstrated the expression of PAR(2) in rat vagal pulmonary sensory neurons. Our patch-clamp study further showed that intracellular application of capsaicin (0.75 mu m) induced single-channel current that exhibited outward rectification in these neurons. The probability of the channel being open (P-o) was significantly increased after the cells were pretreated with PAR(2)-activating peptide (100 mu m, 2 min). Pretreatment with trypsin (0.1 mu m, 2 min) also increased the single-channel P-o, and the effect was completely inhibited by soybean trypsin inhibitor (0.5 mu m, 3 min). In addition, the effect of PAR(2) activation was abolished by either U73122 (1 mu m, 4 min), a phospholipase C inhibitor, or chelerythrine (10 mu m, 4 min), a protein kinase C inhibitor. In conclusion, our data demonstrated that activation of PAR(2) upregulated single-channel activities of TRPV1 and that the effect was mediated through the protein kinase C-dependent transduction pathway.