Expression of P2Y1 receptors in rat taste buds

Extracellular nucleotides such as ATP are the signaling molecules which bind to membrane receptors (P2X ligand-gated ion channels and G-protein-coupled P2Y families). In the gustatory system, it is known that P2X receptors are expressed exclusively in nerve fibers innervating the taste buds. Also, P2Y receptors are suggested to play some important roles in taste signal transductions on the basis of the physiological studies. In the present study, we examined the expression patterns of P2Y(1) receptor subtype by using reverse transcript polymerase chain reaction (RT-PCR), in situ hybridization, and immunohistochemistry. RT-PCR analyses showed that P2Y(1) receptor mRNAs appeared in circumvallate papillae. P2Y(1) receptor mRNA was detected in a subset of taste bud cells by in situ hybridization. By immunohistochemical analyses, P2Y(1) receptor was detected in a subset of taste bud cells of fungiform, foliate, and circumvallate papillae. We showed that ATP induced a biphasic intracellular Ca2+ increase in taste cells by a Ca2+ imaging method. Furthermore, we showed by double-immunolabeling methods that P2Y(1)-expressing cells coexpressed both IP(3)R3 and SNAP-25. These results suggest that ATP may activate P2Y receptors resulting in Ca2+ release from internal stores via IP(3)R3. Since many SNAP-25-immunoreactive taste bud cells coexpressed P2Y(1) immunoreactivity, it is suggested that P2Y(1)-expressing cells may possess synapses with afferent nerve fibers. The results of the present study suggest that P2Y(1) receptor may play some roles in ATP-mediated signal transductions between taste bud cells and afferent taste fibers.