Gustducin-coupled receptor for denatonium and N(6)-propyl-2- thiouracil 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. In airway epithelial cells, binding of denatonium increases the intracellular calcium ion concentration and stimulates ciliary beat frequency. . This is the function of Ensembl gene identifier ENSG00000127364 (TAS2R4, taste 2 receptor member 4).