[Cell surface receptors in digestive epithelial cells]

A large number of peptides (neurodigestive peptides) contributes to the regulation of events in the gastrointestinal tract. The demonstration that these mediators interact with receptors as the first step of a direct cellular effect and that the expression receptors at the cell surface is specific for each type of cells and related to the cell function was decisive advances in the understanding of the digestive physiology. Receptors comprise an extracellular ligand binding domain that recognizes specifically each neurodigestive peptide and which is linked to cytoplasmically oriented catalytic domain which transduces the peptide signal and generates a biochemical message. This organization represent a unique system for allosteric modulation of each regulatory biological signal. The modality of the signal activation and control is different for the 4 main families of ligand sensitive receptors linked to 1) the adenylate cyclase activity, 2) the opening of the ionic channels, 3) the activation of the phospholipase C or possessing 4) an intrinsic protein kinase activity. Finally, the transduced message is modulated according to the dynamic state of stimulation or inhibition triggered through the receptor network of the cell and to ratio of cell surface versus internalized receptors. Therefore, the overall functional physiological effect on the digestive cells depends on the integration of the numerous cell surface events induced by the different receptor-activated signaling pathways characteristic of each cell type. In this minireview, the general characteristics of the neurohormonal regulation of the epithelial function and of the ligand receptor interaction, the cartography of the receptors in the different gastric and intestinal epithelial cells their role in the main digestive function (hydroelectrolytic exchanges, cell secretion of products, cellular growth and mitogenis) are briefly exposed and summarized in tables. Recent advances regarding the oncogenic potential of tyrosine kinase receptors in relation to digestive cancer are summarized.