The calcium-sensing receptor in taste tissue

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Abstract

Calcium is an essential nutrient that induces a distinctive taste quality, but the sensing mechanism of calcium in the tongue is poorly understood. A recent study linked calcium to T1R3 receptor. Here, we propose another system for calcium taste involving the extracellular calcium-sensing receptor (CaSR). This G protein-coupled receptor that responds to calcium and magnesium cations is involved in calcium homeostasis regulating parathyroid and kidney functions. In this study, CaSR was found in isolated taste buds from rats and mice. It was expressed in a subset of cells in circumvallate and foliate papillae, with fewer cells in the fungiform papillae. This is the first evidence in mammals that locates CaSR in gustatory tissue and provides the basis for better understanding not only calcium taste but also the taste of multiple CaSR agonists.

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Materials and methods

Papillae micro-dissection and polymerase chain reaction. Six male Sprague–Dawley rats (2–4 months) and six C57BL/6ByJ (B6) male mice (29–36 g) (Charles River, Japan) were handled according to our laboratory protocol. Briefly, habituation took place for 2 weeks in a controlled temperature (23 ± 1 °C) and 12:12 h light/dark cycle (lights on at 07.00 and off at 19.00 h). Animals had free access to chow and tap water. After euthanasia under anesthesia, the tongue, esophagus, mucosa, stomach and kidney

CASR is expressed in rat and mouse taste tissue

To determine whether CaSR plays a role in calcium or amino acid taste detection, we first studied if the receptor is expressed in taste receptor cells of rodents. RT-PCR of microdissected circumvallate, foliate and fungiform papillae of peeled rat and mouse tongue epithelium showed that CaSR is expressed in gustatory tissue (Fig. 1A and B). This expression was specific to taste cells. The skin of the molar eminence of the tongue that does not have taste buds (non-taste tissue control; CONT) did

Acknowledgments

We thank Dr. Michael Tordoff from the Monell Chemical Senses Center for his valuable comments of the manuscript, Mr. Seikichi Sekine for tissue preparations, and Ms. Mariko Ozawa and Ms. Sachie Otsuka for their technical assistance. Authors are employees of Ajinomoto Co. Inc., which has supported this work.

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