Amylase expression in taste receptor cells of rat circumvallate papillae

The chemical composition of the luminal content is now accepted to have a profound influence on the performance of chemosensory receptors. Gustatory and intestinal chemoreceptors have in common their expression of molecules involved in taste sensing and signal transduction pathways. The recent finding that enterocytes of the duodenal epithelium are capable of expressing luminal pancreatic amylase suggests that taste cells of the gustatory epithelium might, in the same way, express salivary amylase in the oral cavity. Therefore, we investigated amylase expression in rat circumvallate papillae by using analyses involving immunohistochemistry, Western blot, and reverse transcription with the polymerase chain reaction. In addition, we used double-labeling confocal laser microscopy to compare amylase immunolabeling with that of the following markers: protein gene product 9.5 (PGP 9.5) and chromogranin A (CgA) for endocrine cells, alpha-gustducin and phospholipase C beta 2 (PLC beta 2) as taste-signaling molecules, and cystic fibrosis transmembrane regulator (CFTR) and Clara-cell-specific secretory protein of 10-kDa (CC10) as secretory markers. The results showed that amylase was present in some taste bud cells; its immunoreactivity was observed in subsets of cells that expressed CgA, alpha-gustducin, PLC beta 2, CFTR, or CC10. PGP 9.5 immunoreactivity was never colocalized with amylase. The data suggest that amylase-positive cells constitute an additional subset of taste receptor cells also associated with chemoreceptorial and/or secretory molecules, confirming the occurrence of various pathways in taste buds.