Expression of bitter taste receptors of the T2R family in the gastrointestinal tract and enteroendocrine STC-1 cells

TLDR

The gastrointestinal mucosa is known to sense molecules, yet the initial molecular recognition mechanisms that detect luminal contents remain unclear. The study aimed to identify taste receptor gene transcripts in the gastrointestinal tract. Reverse transcriptase–PCR, immunohistochemistry, and functional Ca²⁺ imaging revealed T2R bitter taste receptor transcripts and associated G protein subunits in gastric and duodenal mucosa, enteroendocrine cells, and STC‑1 cells, and showed that bitter compounds rapidly increase intracellular Ca²⁺, confirming functional expression in mouse and rat gastrointestinal tract.

Abstract

Although a role for the gastric and intestinal mucosa in molecular sensing has been known for decades, the initial molecular recognition events that sense the chemical composition of the luminal contents has remained elusive. Here we identified putative taste receptor gene transcripts in the gastrointestinal tract. Our results, using reverse transcriptase–PCR, demonstrate the presence of transcripts corresponding to multiple members of the T2R family of bitter taste receptors in the antral and fundic gastric mucosa as well as in the lining of the duodenum. In addition, cDNA clones of T2R receptors were detected in a rat gastric endocrine cell cDNA library, suggesting that these receptors are expressed, at least partly, in enteroendocrine cells. Accordingly, expression of multiple T2R receptors also was found in STC-1 cells, an enteroendocrine cell line. The expression of α subunits of G proteins implicated in intracellular taste signal transduction, namely Gα gust , and Gα t - 2 , also was demonstrated in the gastrointestinal mucosa as well as in STC-1 cells, as revealed by reverse transcriptase–PCR and DNA sequencing, immunohistochemistry, and Western blotting. Furthermore, addition of compounds widely used in bitter taste signaling (e.g., denatonium, phenylthiocarbamide, 6-n-propil-2-thiouracil, and cycloheximide) to STC-1 cells promoted a rapid increase in intracellular Ca 2+ concentration. These results demonstrate the expression of bitter taste receptors of the T2R family in the mouse and rat gastrointestinal tract.