G Protein [beta][gamma] Complexes in Circumvallate Taste Cells Involved in Bitter Transduction

G protein [beta][gamma] (G[beta][gamma]) complexes are considered to play an important role in second messenger signaling of phospholipase C (PLC). Monitoring the inositol 1,4,5-trisphosphate (IP3) response in circumvallate tissue homogenates upon stimulation with denatonium benzoate, it was demonstrated that a glutathione S-transferase-GRK3ct fusion protein--a G[beta][gamma] scavenger--attenuates the bitter tastant-induced second messenger reaction. Towards an identification of the G[beta][gamma] complex involved in rat bitter taste transduction, it was found that the G protein [beta]3 subtype is specifically expressed in taste receptor cells of circumvallate papillae. G[beta]3-specific antibodies blocked the denatonium benzoate-induced IP3 formation in a dose-dependent manner; the inhibitory effect was reversed by preincubation with the antigenic peptide. A less pronounced inhibition was observed using G[beta]1-specific antibodies. Analyzing individual taste cells by single cell reverse transcriptase-polymerase chain reaction approaches, overlapping expression patterns for PLC[beta]2, G[alpha]gust, G[beta]3 and G[gamma]3 could be demonstrated. Furthermore, the co-expression of all profiled signal transduction components in individual taste receptor cells could be detected. These data support the concept that the denatonium benzoate-induced IP3 response is mediated by an activation of PLC[beta]2 via a G[beta][gamma] complex, possibly composed of G[beta]3 as the predominant [beta] subunit and G[gamma]3, and imply that multiple second messenger pathways may exist in individual taste receptor cells.