Immunohistochemical Localization of Cystic Fibrosis Transmembrane Regulator and Clara Cell Secretory Protein in Taste Receptor Cells of Rat

Taste receptor cells (TRCs) are the sensory cells of taste transduction and are organized into taste buds embedded in the epithelium of the tongue, palate, pharynx, and larynx. Several studies have demonstrated that TRCs involved in sweet as well as bitter and umami responses express a-gustducin, an a-subunit of the G-protein complex. It has been further demonstrated that this typical taste protein is a potent marker of chemosensory cells located in several tissues, including gastric and pancreatic mucosa and the respiratory apparatus. We recently observed that a-gustducin and phospholipase C beta 2–immunoreactive cells were colocalized in the airways with cystic fibrosis transmembrane regulator (CFTR) and Clara cell–specific secretory protein of 10 (CC10) and 26 kDa (CC26). This finding suggests that TRCs might themselves express secretory markers. To test this hypothesis, we investigated the expression of CFTR, CC10, and CC26 in rat circumvallate papillae using reverse transcrip-tase–polymerase chain reaction analysis, immunohistochemistry, and confocal laser microscopy. The results showed that secre-tory markers such as CFTR, CC10, and CC26 are present in taste cells of rat circumvallate papillae, and their immunoreactivity is expressed, to a different extent, in subsets of taste cells that express a-gustducin. The presence of CFTR, CC10, and CC26 in taste bud cells and their coexpression pattern with a-gustducin confirms and extends our previous findings in airway epithelium