International Union of Basic and Clinical Pharmacology. CXVII: Taste 2 receptors-Structures, functions, activators, and blockers.

For most vertebrates, bitter perception plays a critical role in the detection of potentially harmful substances in food items. The detection of bitter compounds is facilitated by specialized receptors located in the taste buds of the oral cavity. This work focuses on these receptors, including their sensitivities, structure-function relationships, agonists, and antagonists. The existence of numerous bitter taste receptor variants in the human population and the fact that several of them profoundly affect individual perceptions of bitter tastes are discussed as well. Moreover, the identification of bitter taste receptors in numerous tissues outside the oral cavity and their multiple proposed roles in these tissues are described briefly. Although this work is mainly focused on human bitter taste receptors, it is imperative to compare human bitter taste with bitter taste of other animals to understand which forces might have shaped the evolution of bitter taste receptors and their functions and to distinguish apparently typical human features from rather general ones. For readers who are not very familiar with the gustatory system, short descriptions of taste anatomy, signal transduction, and oral bitter taste receptor expression are included in the beginning of this article. SIGNIFICANCE STATEMENT: Apart from their role as sensors for potentially harmful substances in the oral cavity, the numerous additional roles of bitter taste receptors in tissues outside the gustatory system have recently received much attention. For careful assessment of their functions inside and outside the taste system, a solid knowledge of the specific and general pharmacological features of these receptors and the growing toolbox available for studying them is imperative and provided in this work.