Taste receptor-like cells in the rat gut identified by expression of alpha-gustducin.

Abstract

The a-subunit of the trimeric G-protein complex specific for taste receptor cells of the tongue, a-gustducin, is described here to be also expressed in the stomach and intestine. The a-gustducin-containing cells were identified as brush cells that are scattered throughout the surface epithelium of the gut and share structural features of taste receptor cells of the tongue. These findings provide clues to the long-sought molecular and cellular basis for chemoreception in the gut.It is generally believed that the epithelium lining the inner surface of the gut can sense chemical components of the lumenal contents. This chemosensory information appears to be important for the regulation of various aspects of gastrointestinal secretion, resorption, and motility (1, 2). Classical examples of intestinal chemosensitivity are the dependence of gastric emptying on the chemical nature of the nutrients present in the small intestine and the involvement of chemical preabsorption information in short-term regulation of food intake (2). The cellular and molecular basis for chemoreception in the gut is hitherto unknown. In this study we addressed the question ofwhether the epithelium of the gut might express a-gustducin, the GTP-binding a-subunit of a trimeric Gprotein complex that is specific for taste receptor cells of the tongue (3). Here we show that a-gustducin is also expressed in the epithelium of the gut where it is associated with a specialized cell type long known under the names brush cell, tufted cell, or caveolated cell (4-6). The function of this cell type, which is present in humans, rats, and probably all other mammals, had been enigmatic until now. MATERIALS AND METHODSAntibodies and Immunostaining. A polyclonal antibody specific for a-gustducin was raised in a rabbit immunized with a synthetic peptide comprising amino acid residues 92-113 of the rat a-gustducin sequence (3). This sequence stretch is unique for a-gustducin and is not present in the sequences of any other known G-protein. Antibodies were affinity-purified to the peptide adsorbed to nitrocellulose (7,8). Polyclonal rabbit antibodies specific for chromogranin A and serotonin (9) and mouse monoclonal antibodies to villin (Dianova, Hamburg, Germany) and cytokeratin 18 (Progen, Heidelberg) were also used in this study. Indirect immunofluorescence was applied to 1-,um thick tissue sections of quick-frozen and Epon-embedded tissues as described (8). For doubleimmunofluorescence sections were incubated with a mixture of the rabbit antibody against a-gustducin and mouse monoclonal antibodies either specific for villin or cytokeratin 18. Primary antibodies were diluted with PBS: anti-gustducin (1:200), anti-chromogranin (1:4,000), anti-serotonin (1:10,000), anti-villin (0.1 /Lg/ml-1), anti-cytokeratin 18 (0.5 ,ug/ml-1). As secondary antibodies fluorescein isothiocyanate-labeled goat anti-mouse IgG and tetramethylrhodamine isothiocyanate-labeled goat anti-rabbit IgG (Dianova) were used at concentrations of 0.1 Ag/ml-1.Immunoblotting. Various tissue...

Bitter taste receptors and α-gustducin regulate the secretion of ghrelin with functional effects on food intake and gastric emptying

“…The discovery that taste receptors and their downstream effectors exist in the gut raised the intriguing possibility that the gut is able to "taste" luminal contents (19). Sensing of the luminal content is important to initiate the appropriate response of digestion and absorption of nutrients or neutralization and expulsion of drugs, toxins, and microorganisms but also for food control, which is regulated via the gut-brain axis.…”

“…Samples were extracted on a Sep-Pak C18 cartridge (Waters Corporation) and vacuum-dried. The radioimmunoassay was performed with 125 I[Tyr 24 ] human ghrelin as a tracer and with a rabbit antibody raised against human ghrelin [14][15][16][17][18][19][20][21][22][23][24][25][26][27][28] (Ab2066, final dilution 1:3,000), which recognizes both octanoylated and desoctanoylated ghrelin. For the determination of octanoylated ghrelin, a rabbit antibody against human ghrelin [1][2][3][4][5][6][7][8] was used (Ab5004, final dilution 1:100.000), which did not crossreact with desoctanoyl ghrelin.…”

Expression of the putative membrane fatty acid transporter (FAT) in taste buds of the circumvallate papillae in rats

“…~-Gustducin, which is the 0~-subunit of trimeric GTP-binding protein complex expressed in taste buds [31], is also t\mnd in the intestinal epithelimn [32]. Since c~-gustducin participates in intraccllular signal transfer of bitterness and sweetness by acting with the taste receptors on cell membrane [33], the chcmoperception mechanism for the diet-derived molecules in taste cells is considered similar to thai in the digestive tract.…”

In focus in HCB: from cell biology to tissue structure and function

“…Brand-Saberi and Zaehres present an enlightening account of how "anatomy, as a descriptive topic of research and instruction in medicine, has been influenced by recent discoveries in molecular cell and developmental biology", highlighting particularly the impact of stem cell research (Brand-Saberi and Zaehres 2016). The "brush cell", an epithelial cell for which a chemosensory function was first supported by findings of Drenckhahn's group (Höfer et al 1996), is the topic of a review by Deckmann and Kummer, who assess morphological, biochemical and functional characteristics of chemosensory cells in the urethra (Deckmann and Kummer 2016). Schnittler portrays developments in research on contraction of endothelial cells, and on formation and control of endothelial intercellular junctions (Schnittler 2016).…”