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

Bitter perception plays a critical role for the detection of potentially harmful substances in food items for most vertebrates. The detection of bitter compounds is facilitated by specialized receptors located in taste buds of the oral cavity. This work focuses on the receptors, including their sensitivities, structure-function relationships, agonists and antagonists. Moreover, the existence of numerous bitter taste receptor variants in the human population and the fact that several of them affect individual bitter tasting profoundly, is discussed as well. The identification of bitter taste receptors in numerous tissues outside the oral cavity and their multiple proposed roles in these tissues is also described briefly. Although this work is mainly focused on human bitter taste receptors, it is imperative to compare human bitter taste with that of other animals to understand which evolutionary forces might have shaped bitter taste receptors and their functions and to distinguish apparent typical human from rather general features. For the readers who are not too 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 received much attention recently. For the careful assessment of functions inside and outside the taste system a solid knowledge about the specific and general pharmacological features of these receptors and the growing toolbox available for studying them is imperative and provided in this work.