Effect of five taste ligands on the release of CCK from an enteroendocrine cell line, STC-1.

Here, we investigated which taste ligand induces the CCK (cholecystokinin) release from intestinal STC-1 cells. We first developed a new assay to measure the release of CCK. The expression vector for CCK type A receptor (CCKAR) was permanently introduced into HEK293T cells and a cell line was established (CCKAR/HEK). Then, STC-1 cells were treated with taste ligands and the incubated buffer of STC-1 cells containing released CCK was applied to CCKAR/HEK cells.Since CCKAR couples to Gq-signaling, the CCK-induced receptor activation can be monitored by the method of Ca2+-imaging. Therefore, when CCK is released from STC-1 cells to culture medium with taste stimulation, Ca2+ activation of CCKAR/HEK should be observed. Among five different taste ligands (saccharin, Na-glutamate, NaCl, denatonium benzoate, HCl), only denatonium benzoate and HCl induced the release of CCK in STC-1 cells. Thus, we found that only specific taste ligands induce the CCK release, and that other three taste ligands cannot induce the release of CCK despite of their ability to elevate the intracellular Ca2+ level in STC-1 cells.