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

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 IP(3), 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 IP(3) receptor subtype in this pathway is not known. In the present study we used immunocytochemistry on rodent taste tissue to identify the IP(3) receptors expressed in taste cells and to examine taste bud expression patterns for IP(3)R3. RESULTS: Antibodies against Type I, II, and III IP(3) receptors were tested on sections of rat and mouse circumvallate papillae. Robust cytoplasmic labeling for the Type III IP(3) receptor (IP(3)R3) 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 IP(3) receptors. To investigate the potential role of IP(3)R3 in bitter taste transduction, we used double-label immunocytochemistry to determine whether IP(3)R3 is expressed in the same subset of cells expressing other bitter signaling components. IP(3)R3 immunoreactive taste cells were also immunoreactive for PLCβ2 and γ13. Alpha-gustducin immunoreactivity was present in a subset of IP(3)R3, PLCβ2, and γ13 positive cells. CONCLUSIONS: IP(3)R3 is the dominant form of the IP(3) receptor expressed in taste cells and our data suggest it plays an important role in bitter taste transduction.

研究背景：味觉受体细胞负责将化学刺激转换为电信号，进而引发味觉感知。味觉转导过程中的重要第二信使为肌醇三磷酸（IP₃），其参与苦味与甜味的转导通路。目前已鉴定出苦味转导通路的多种组分，包括T2R/TRB味觉受体、磷脂酶Cβ2以及G蛋白亚基α-味觉转导蛋白（α-gustducin）、β3与γ13。然而，该通路中IP₃受体亚型的具体身份仍未明确。本研究通过对啮齿类动物味觉组织实施免疫细胞化学检测，以鉴定味觉细胞中表达的IP₃受体，并探究IP₃R3在味蕾中的表达模式。
研究结果：针对I型、II型与III型IP₃受体的抗体分别在大鼠和小鼠的轮廓乳头切片上进行了测试。在两个物种的大量味觉细胞亚群中，均观察到III型IP₃受体（IP₃R3）呈现显著的胞质标记信号。与之相反，针对I型或II型IP₃受体的抗体几乎未检测到免疫反应信号。为探究IP₃R3在苦味转导中的潜在作用，本研究采用双标记免疫细胞化学法，以确定IP₃R3是否与其他苦味信号通路组分在同一细胞亚群中表达。表达IP₃R3的免疫反应阳性味觉细胞，同时也呈现PLCβ2与γ13的免疫阳性反应。α-味觉转导蛋白的免疫阳性信号则存在于部分IP₃R3、PLCβ2及γ13阳性细胞中。
研究结论：IP₃R3是味觉细胞中表达的主要IP₃受体亚型，本研究数据表明其在苦味味觉转导过程中发挥重要作用。