Chemical Senses Advance Access originally published online on March 1, 2005
Chemical Senses 2005 30(4):281-290; doi:10.1093/chemse/bji022
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Characterization of Bitter Taste Responses of Intestinal STC-1 Cells
1 Department of Bio-Science, Faculty of Bio-Science, Nagahama Institute of Bio-Science and Technology, 1266 Tamura-cho, Nagahama-shi, Shiga 526-0829, Japan, 2 Graduate School of Science and Technology, Chiba University, Yayoi-cho, Inage-ku, Chiba 263-8522, Japan and 3 Division of Biophysics and Neurobiology, Department of Molecular Physiology, National Institute for Physiological Sciences, 38 Nishigonaka Myodaiji, Okazaki, Aichi 444-8585, Japan
Correspondence to be sent to: Osamu Saitoh, Department of Bio-Science, Faculty of Bio-Science, Nagahama Institute of Bio-Science and Technology, 1266 Tamura-cho, Nagahama-shi, Shiga 526-0829, Japan. e-mail: o_saito{at}nagahama-i-bio.ac.jp
Cellular responses of STC-1 cells to two bitter tastants (denatonium and caffeine) were investigated using a calcium-imaging technique and compared with the response to bombesin. Caffeine is known to stimulate taste receptor cells, but the properties of its signaling have not been well studied. STC-1 cells responded to all three molecules in a dose-dependent manner, and when a reverse transcriptase–polymerase chain reaction (RT–PCR) for denatonium receptor was performed, the product of predicted size was detected in STC-1 cells. Furthermore, all three signaling pathways were blocked by a phospholipase C (PLC) inhibitor, demonstrating the essential involvement of PLC in cellular responses. To study the regulatory system of G protein signaling in STC-1 cells, we searched G protein-coupled receptor kinases (GRKs) by the degenerate-primer PCR method and found that GRK2 is expressed. We also demonstrated that three GRKs (GRK2, GRK3 and GRK5) are differentially distributed in the circumvallate papilla while only GRK2 is present in taste bud cells. Finally, we overexpressed GRK2 in SCT-1 cells and found that bombesin-induced response was strongly inhibited by GRK2 but denatonium-activated signaling was not affected. In the case of caffeine, response was decreased by expression of GRK2 only when cells were activated by 1 mM caffeine. Thus, we showed that STC-1 cells emerge as a cell model for studying the molecular mechanism of bitter taste signaling, and could indicate properties of caffeine-induced signaling in comparison with other signaling.
Key words: denatonium, caffeine, dose-response relationship, U-73122, GRK, circumvallate papilla
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