Gustducin-coupled receptor implicated in the perception of bitter compounds in the oral cavity and the gastrointestinal tract. Signals through PLCB2 and the calcium-regulated cation channel TRPM5 (By similarity). In airway epithelial cells, binding of denatonium increases the intracellular calcium ion concentration and stimulates ciliary beat frequency (By similarity). In airway epithelial cells, localizes to motile cilia. Several bitter taste receptors are expressed in a single taste receptor cell. Belongs to the G-protein coupled receptor T2R family.