Expression of taste receptors in Solitary Chemosensory Cells of rodent airways

We utilized a combination of immunohistochemistry and molecular techniques (rtPCR and in situ hybridization) on rats and transgenic mice where the Tas1R3 or TRPM5 promoter drives expression of green fluorescent protein (GFP).Epithelial SCCs specialized for chemoreception are distributed throughout much of the respiratory tree of rodents. These cells express elements of the taste transduction cascade, including Tas1R and Tas2R receptor molecules, α-gustducin, PLCβ2 and TrpM5. The Tas2R bitter taste receptors are present throughout the entire respiratory tract. In contrast, the Tas1R sweet/umami taste receptors are expressed by numerous SCCs in the nasal cavity, but decrease in prevalence in the trachea, and are absent in the lower airways.Elements of the taste transduction cascade including taste receptors are expressed by SCCs distributed throughout the airways. In the nasal cavity, SCCs, expressing Tas1R and Tas2R taste receptors, mediate detection of irritants and foreign substances which trigger trigeminally-mediated protective airway reflexes. Lower in the respiratory tract, similar chemosensory cells are not related to the trigeminal nerve but may still trigger local epithelial responses to irritants. In total, SCCs should be considered chemoreceptor cells that help in preventing damage to the respiratory tract caused by inhaled irritants and pathogens.Chemical irritation of the respiratory and tracheal mucosa causes various reflex responses such as coughing and apnea. Similarly, chemical stimulation of the larynx results in a number of protective reflexes involved in respiratory regulation, including startle, swallowing, apnea, laryngeal constriction, hypertension, and bradycardia [1-7]. Such disturbance of respiration, if prolonged, may cause profound hypoxemia and even death [8,9]. Despite obvious physiological and clinical importance, not enough information is available regarding the means by which chemical irritants are detected.Until recently, the presump