Trpm5 is a novel transient receptor potential channel expressed in taste receptor cells

The sense of taste plays a critical role in the life and nutritional status of organisms. During the last decade, several molecules involved in taste detection and transduction have been identified, providing a better understanding of the molecular physiology of taste receptor cells. However, a comprehensive catalogue of the taste receptor cell machinery is still unavailable. The Margolskee group has recently identified Trpm5, using differential screening of cDNAs from individual taste receptor cells. Trpm5 is a novel candidate taste transduction element belonging to the mammalian family of transient receptor potential channels. Trpm5 is expressed in a tissue-restricted manner, with high levels in gustatory tissue. In taste cells, Trpm5 is co-expressed with taste-signaling molecules such as α-gustducin, Gγ₁₃, phospholipase C β₂ and inositol 1,4,5-trisphosphate receptor type III. Biophysical studies of Trpm5 heterologously expressed in Xenopus oocytes and mammalian CHO-K1 cells indicate that it functions as a store-operated channel that mediates capacitative calcium entry. Additionally, it was shown that the bitter-responsive enteroendocrine cell line STC-1 expresses multiple transient receptor potential channels and that capacitative calcium entry is necessary for its chemosensory function. The role of Trpm5 and other transient receptor potential channels in capacitative calcium entry in taste receptor cells in response to bitter and/or sweet compounds is discussed.