Introduction and Aims The TRPA1 ion channel is thought to have an important role in the cough reflex. It has been demonstrated that agonisation of TRPA1 receptors by inhalation of cinnamaldehyde, a specific agonist of TRPA1, induces cough in normal human volunteers. We wanted to determine the expression and characterisation of the TRPA1 receptor in human lung tissue.

Methods Bronchial biopsies were obtained from patients with the Cough Hypersensitivity Syndrome on fibre-optic bronchoscopy. Biopsies were obtained from a major bronchus. Lung resection samples were obtained from patients undergoing surgery for lung cancer. Dorsal root ganglia were used as a positive control. These tissue samples were analysed by immunohistochemistry with a specific TRPA1 antibody.

Results Samples from 14 patients (11 males, mean age 56 years) with the Cough Hypersensitivity Syndrome and 10 lung resection samples (6 males, mean age 68 years) were obtained. All the tissue samples stained for TRPA1. The TRPA1 stain was avidly taken up by the bronchial epithelium, smooth muscle bundles and nerve tissue.

Conclusion We have described the distribution of the TRPA1 ion channel in lung tissue. TRPA1 is agonised by several environmental irritants and endogenous mediators of inflammation. The presence of TRPA1 ion channel in bronchial mucosal nerves and epithelium suggests an important role in the cough reflex. The identification of these ion channels on smooth muscle could suggest a role in asthmatic inflammation as well.