Mammals have 3 pairs of major salivary glands i.e., the parotid, submandibular, and sublingual glands. Saliva secretion of these glands is modulated by taste perception. Salivary glands are composed mainly of acinar and ductal cells. Primary saliva is secreted by acinar cells and modified during ductal flow. Recently, of the murine 35 bitter taste receptors, Tas2r108 was expressed at highest levels in the submandibular gland by qPCR. Further, Tas2r108-transfected cells respond to a range of bitter compounds, such as denatonium, quinine, colchicine, diphenidol, caffeine and dapson. The objective of the present study was to characterize the expression of Tas2r108 mRNA in acinar and/or ductal cells of the submandibular gland using in situ hybridization (ISH). Male 42-60 days old DBA2 mice were used in the study. Messenger RNAs were extracted from the submandibular gland for generating digoxigenin (DIG) labeled-cRNA probes. These probes were transcribed in anti-sense and sense orientation using T7 RNA polymerase. Dot blot hybridization was performed using DIG labeled-cRNA probes, in order to estimate integrity and optimal diluting concentration of these probes. Subsequently, ISH was performed on murine submandibular gland to detect Tas2r108 mRNA. Dot blot hybridization data demonstrated that Tas2r108 DIG labeled-cRNA anti-sense probes specifically detected Tas2r108 cDNA. ISH results showed that the anti-sense probes labeled acinar and ductal cells in the submandibular gland, whereas no staining was visible in sense controls. Interestingly, the Tas2r108 expression levels were higher in acinar than ductal cells. These results suggested that Tas2r108 might be more associated with primary saliva secretion than with ductal modification of saliva composition.

The nasal cavity encounters various irritants during inha¬lation such as dust and pathogens. To detect and remove these irritants, it has been postulated that the nasal mucosa epithelium has a specialized sensing system. The oral cavity, on the other hand, is known to have bitter taste receptors (T2Rs) that can detect harmful substances to prevent ingestion. Recently, solitary chemosensory cells expressing T2R subtypes have been found in the respiratory epithelium of rodents. In addition, T2Rs have been identified in the human airway epithelia. However, it is not clear which T2Rs are expressed in the human nasal mucosa epithelium and whether they mediate the removal of foreign materials through increased cilia movement. In our current study, we show that human T2R receptors indeed function also in the nasal mucosa epithelium. Our RT-PCR data indicate that the T2R subtypes (T2R3, T2R4, T2R5, T2R10, T2R13, T2R14, T2R39, T2R43, T2R44, T2R 45, T2R46, T2R47, T2R48, T2R49, and T2R50) are expressed in human nasal mucosa. Furthermore, we have found that T2R receptor activators such as bitter chemicals augments the ciliary beating frequency. Our results thus demonstrate that T2Rs are likely to function in the cleanup of inhaled dust and pathogens by increasing ciliary movement. This would suggest that T2Rs are feasible molecular targets for the development of novel treatment strategies for nasal infection and inflammation.