Functional characterization of the bovine sour taste receptor Otopetrin 1 (OTOP1) in response to dietary and ruminal acids

Cattle frequently consume acidic feeds such as silage and are continuously exposed to acidic substances originating from ruminal fermentation during rumination. These acids are presumed to be detected <i>via</i> sour taste receptors expressed in taste buds; however, the functional properties of bovine sour taste receptors remain poorly understood. In this study, we focused on the bovine sour taste receptor candidate Otopetrin 1 (OTOP1) and characterized its functional responses to physiologically relevant dietary and ruminal acids, as well as its modulation by zinc ions. Bovine OTOP1 was heterologously expressed in HEK293T cells, and its acid responsiveness was evaluated using whole-cell patch clamp and membrane potential assays. Cells expressing bovine OTOP1 exhibited pH-dependent inward currents in response to HCl. In addition, bovine OTOP1 was activated by a range of organic acids present in cattle feed and the rumen, including formic, citric, malic, tartaric, lactic, acetic, butyric, and propionic acids. Furthermore, acid-induced OTOP1 currents were inhibited by zinc ions in a concentration-dependent manner. These findings demonstrate that bovine OTOP1 can function as a sour taste receptor responsive to multiple physiologically relevant acidic compounds.