Immunocytochemical evidence for co-expression of Type III IP 3 receptor with signaling components of bitter taste transduction

摘要

Background Taste receptor cells are responsible for transducing chemical stimuli into electrical signals that lead to the sense of taste. An important second messenger in taste transduction is IP₃, which is involved in both bitter and sweet transduction pathways. Several components of the bitter transduction pathway have been identified, including the T2R/TRB taste receptors, phospholipase C β2, and the G protein subunits α-gustducin, β3, and γ13. However, the identity of the IP₃ receptor subtype in this pathway is not known. In the present study we used immunocytochemistry on rodent taste tissue to identify the IP₃ receptors expressed in taste cells and to examine taste bud expression patterns for IP₃R3. Results Antibodies against Type I, II, and III IP₃ receptors were tested on sections of rat and mouse circumvallate papillae. Robust cytoplasmic labeling for the Type III IP₃ receptor (IP₃R3) was found in a large subset of taste cells in both species. In contrast, little or no immunoreactivity was seen with antibodies against the Type I or Type II IP₃ receptors. To investigate the potential role of IP₃R3 in bitter taste transduction, we used double-label immunocytochemistry to determine whether IP₃R3 is expressed in the same subset of cells expressing other bitter signaling components. IP₃R3 immunoreactive taste cells were also immunoreactive for PLCβ2 and γ13. Alpha-gustducin immunoreactivity was present in a subset of IP₃R3, PLCβ2, and γ13 positive cells. Conclusions IP₃R3 is the dominant form of the IP₃ receptor expressed in taste cells and our data suggest it plays an important role in bitter taste transduction.