Previous studies indicated that the peptide substance P (SP) causes Cl−-dependent secretion in animal colonic mucosa. We investigated the effects of SP in human colonic mucosa mounted in Ussing chamber. Drugs for pharmacological characterization of SP-induced responses were applied 30 min before SP. Serosal, but not luminal, administration of SP (10−8 to 10−6 M) induced a rapid, monophasic concentration and Cl−-dependent, bumetanide-sensitive short-circuit current ( I sc) increase, which was inhibited by the SP neurokinin 1 (NK1)-receptor antagonist CP-96345, the neuronal blocker TTX, the mast cell stabilizer lodoxamide, the histamine 1-receptor antagonist pyrilamine, and the PG synthesis inhibitor indomethacin. SP caused TTX- and lodoxamide-sensitive histamine release from colonic mucosa. Two-photon microscopy revealed NK1(SP)-receptor immunoreactivity on nerve cells. The tyrosine kinase inhibitor genistein concentration dependently blocked SP-induced I sc increase without impairing forskolin- and carbachol-mediated I sc increase. We conclude that SP stimulates Cl−-dependent secretion in human colon by a pathway(s) involving mucosal nerves, mast cells, and the mast cell product histamine. Our results also indicate that tyrosine kinases may be involved in this SP-induced response.

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Background-Strains of Bacteroides fragilis producing a 20 kDa protein toxin (B fragilis toxin (BFT) or fragilysin) are associated with diarrhoea in animals and humans. Although in vitro results indicate that BFT damages intestinal epithelial cells in culture, the eVects of BFT on native human colon are not known. Aims-To examine the electrophysiological and morphological eVects of purified BFT-2 on human colonic mucosa in vitro. Methods-For resistance (R) measurements, colonic mucosa mounted in Ussing chambers was exposed to luminal or serosal BFT-2 (1.25-10 nM) and after four hours morphological damage was measured on haematoxylin and eosin stained sections using morphometry. F actin distribution was assessed using confocal microscopy. Results-Serosal BFT-2 for four hours was four-, two-, seven-, and threefold more potent than luminal BFT-2 in decreasing resistance, increasing epithelial 3 Hmannitol permeability, and damaging crypt and surface colonocytes, respectively (p<0.05). Confocal microscopy showed reduced colonocyte F actin staining intensity after exposure to BFT-2. Conclusions-BFT-2 increases human colonic permeability and damages human colonic epithelial cells in vitro. These eVects may be important in the development of diarrhoea and intestinal inflammation caused by B fragilis in vivo. (Gut 1999;44:504-510)