Expression of adenosine A2b receptor in rat type II and III taste cells

We previously demonstrated that equilibrative nucleoside transporter 1 was expressed in taste cells, suggesting the existence of an adenosine signaling system, but whether or not the expression of an adenosine receptor occurs in rat taste buds remains unknown. Therefore, we examined the expression profiles of adenosine receptors and evaluated their functionality in rat circumvallate papillae. Among adenosine receptors, the mRNA for an adenosine A2b receptor (A2bR) was expressed by the rat circumvallate papillae, and its expression level was significantly greater in the circumvallate papillae than in the non-taste lingual epithelium. A2bR-immunoreactivity was detected primarily in type II taste cells, and partial, but significant expression was also observed in type III ones, but there was no immunoreactivity in type I ones. The cAMP generation in isolated epithelium containing taste buds treated with 500 mu M adenosine or 10 mu M BAY60-6583 was significantly increased compared to in the controls. These findings suggest that adenosine plays a role in signaling transmission via A2bR between taste cells in rats.