AbstractIn vertebrates, the extracellular calcium-sensing receptor (CaSR) plays a key role in calcium homeostasis by sensing slight changes in extracellular Ca²⁺. CaSR is also expressed in mammals including rodent taste cells and is involved in sensing kokumi, a rich, savory quality that enhances the intensities of salty, sweet, and umami tastes. In this study, we focused on chicken CaSR (cCaSR) since calcium is an essential nutrient that is necessary for making eggshell and for the extremely rapid initial growth of bones. First we confirmed that cCaSR is expressed in taste cells. Next we cloned the cCaSR gene from kidney and transiently transfected human embryonic kidney 293 T (HEK293T) cells with the recombinant cCaSR, or empty vector and looked for the agonists and allosteric modulators (including kokumi substances) of cCaSR by Ca²⁺ imaging. We found that cCaSR was activated by extracellular Ca²⁺ and Mg²⁺ in a dose dependent manner. Several L-amino acids and kokumi substances such as glutathione enhanced the response of cCaSR. In addition, NPS2143 as a negative allosteric modulator of human CaSR negatively modulated the response of cCaSR. These results suggest that cCaSR can sense extracellular Ca²⁺ and Mg²⁺ as well as positive and negative allosteric modulators. Taken together, the results imply that CaSR might be a multifunctional receptor for calcium, amino acids, and kokumi substances in chicken. The present finding that functional CaSR is expressed in the chicken oral tissues will allow us to further elucidate the physiological role of CaSR in the chickens' taste sense, and to create new feeds that will contribute to the poultry industry.