The effect of Xenin25 on spontaneous circular muscle contractions of rat distal colon in vitro

Physiological roles of chloride ions in bodily and cellular functions

Physiological roles of Cl-, a major anion in the body, are not well known compared with those of cations. This review article introduces: (1) roles of Cl- in bodily and cellular functions; (2) the range of cytosolic Cl- concentration ([Cl-]c); (3) whether [Cl-]c could change with cell volume change under an isosmotic condition; (4) whether [Cl-]c could change under conditions where multiple Cl- transporters and channels contribute to Cl- influx and efflux in an isosmotic state; (5) whether the change in [Cl-]c could be large enough to act as signals; (6) effects of Cl- on cytoskeletal tubulin polymerization through inhibition of GTPase activity and tubulin polymerization-dependent biological activity; (7) roles of cytosolic Cl- in cell proliferation; (8) Cl--regulatory mechanisms of ciliary motility; (9) roles of Cl- in sweet/umami taste receptors; (10) Cl--regulatory mechanisms of with-no-lysine kinase (WNK); (11) roles of Cl- in regulation of epithelial Na+ transport; (12) relationship between roles of Cl- and H+ in body functions.

Minimum biological domain of xenin-25 required to induce anion secretion in the rat ileum

Xenin-25 has a variety of physiological functions in the gastrointestinal tract, including ion transport and motility. Xenin-25 and neurotensin show sequence homology, especially near their C-terminal regions. The sequence similarity between xenin-25 and neurotensin indicates that the effects of xenin-25 is mediated by the neurotensin receptor but some biological actions of xenin-25 are independent. We have previously reported that xenin-25 modulates intestinal ion transport and colonic smooth muscle activity. However, minimal biological domain of xenin-25 to induce ion transport was not clear. To improve the mechanistic understanding of xenin-25 and to gain additional insights into the functions of xenin-25, the present study was designed to determine the minimal biological domain of xenin-25 required for ion transport in the rat ileum using various truncated xenin fragments and analogues in an Ussing chamber system. The present results demonstrate that the minimum biological domain of xenin-25 to induce Cl-/HCO3- secretion in the ileum contains the C-terminal pentapeptide. Furthermore, Arg at position 21 is important to retain the biological activity of xenin-25 and induces Cl-/HCO3- secretion in the rat ileum.