Expression of alpha-transducin, a chemoreceptive molecule, in endocrine and non-endocrine cells of the pig gastrointestinal tract

Several neural and humoral mechanisms are known to control gut functions before, during and after food ingestion and digestion. Different specialized epithelial cells, i.e. cells that form gustatory buttons distributed throughout the oral cavity, tongue, pharynx, and epiglottis are involved in taste perception. Gustatory cells are able to discriminate different gustatory stimuli: bitter, sweet, salty and sour. Monosodium glutamate and disodium guanylate represent another type of stimulus referred to as umami. Each of these stimuli can be transduced with different modalities, in such a way that gustatory substances can act on peculiar ionic channels (i.e. salty and sour) or via G-protein coupled taste receptors (TR), i.e. TR1 and TR2 (for sweet and bitter, respectively). The activation of these receptors elicits the depolarization of gustatorycells through secondary messenger pathways. The presence of cells expressing TRs, able to discriminate different types of tastes, has been described along the gastrointestinal tract (Rozengurt and Sternini 2007) and in some segments of the respiratory system (Osculati et al. 2007) of several animal species, such as mice and rats as well as in humans. The perception of sweet and bitter is based on the activation of two TR linked Gproteins, such as α- transducin and α-gustducin. The aim of the present study was to examine: 1) the presence and distribution of α-transducin in the pig gastrointestinal (GI) tract; 2) the characterization of cells expressing α-transducin; 3) the relationship between α-transducin cells and nerve fibers supplying the GI tract mucosa.