2--3--o-(2-4-6-trinitrophenyl)adenosine-5--triphosphate and Irritable-Bowel-Syndrome

Increased sensitivity of the afferent innervation of the gastrointestinal tract reportedly underlies symptoms of discomfort and pain in functional bowel disorders. The present investigation aimed to examine whether the purinergic P2X(2) and P2X(3) receptor subunits contribute to the mechanosensitivity of small intestinal afferents in normal mice and in a murine model of postinfectious gut dysfunction. Mesenteric afferent nerve activity was recorded in a mouse jejunum preparation maintained in vitro. As has been shown previously, ramp distension of the jejunal segment evoked biphasic afferent discharge, reflecting activation of low and high threshold fibres. The average pressure-afferent response curve in mice deficient in both P2X(2) and P2X(3) subunits (n = 14) was not significantly different from that of the wild-type control preparations (n = 13). Application of pyridoxal 5-phosphate 6-azophenyl-2 ,4-disulphonic acid (PPADS) (30 micromol L(-1)), a P2X and P2Y antagonist, or 2,4,6-trinitrophenol-adenosine 5'-triphosphate (10 micromol L(-1)), an antagonist selective for homomeric P2X(3) and heteromeric P2X(2/3) receptors, had no effect on the averaged pressure-afferent response curve in wild-type animals. In Trichinella spiralis-infected mice, the magnitude of mesenteric afferent responses to jejunal distension was greater at day 21 and day 56 postinfection compared with the sham control preparations demonstrating the development of afferent hypersensitivity. PPADS had no significant effect upon mechanically evoked afferent discharge rates in sham treated preparations (n = 5), but significantly inhibited afferent sensitivity to jejunal distension in preparations from mice at day 21 (n = 6) and day 56 (n = 7) postinfection. These results suggest that purinergic mechanisms play no role in mechanosensory transduction in the normal small intestine but contribute significantly to postinfectious mechano-hypersensitivity.

Topics: Adenosine Triphosphate; Animals; Fluorescent Dyes; Hypersensitivity; Intestine, Small; Irritable Bowel Syndrome; Mesentery; Mice; Mice, Inbred C57BL; Mice, Knockout; Neurons, Afferent; Physical Stimulation; Purinergic Agonists; Purinergic Antagonists; Purinergic P2 Receptor Agonists; Purinergic P2 Receptor Antagonists; Pyridoxal Phosphate; Receptors, Purinergic; Receptors, Purinergic P2; Receptors, Purinergic P2X2; Receptors, Purinergic P2X3; Signal Transduction; Trichinella spiralis; Trichinellosis

Irritable bowel syndrome (IBS) is a common gastrointestinal disorder characterised by abdominal pain and bloating in association with altered bowel movements. Its pathogenesis and the underlying molecular mechanisms of visceral hyperalgesia remain elusive. Recent studies of somatic and other visceral pain models suggest a role for purinergic signalling mediated by the P2X receptor (P2XR) family.. To examine the role of P2XR signalling in the pathogenesis in a rat model of IBS-like visceral hyperalgesia.. Visceral hypersensitivity was induced by colonic injection of 0.5% acetic acid (AA) in 10-day-old rats and experiments were conducted at 8 weeks of age. Dorsal root ganglion (DRG) neurons innervating the colon were labelled by injection of DiI (1,1'-dioleyl-3,3,3',3-tetramethylindocarbocyanine methanesulfonate) fluorescence into the colon wall.. Visceral hypersensitivity was reversed by TNP-ATP (2'-(or-3')-O-(trinitrophenyl) ATP), a potent P2X1, P2X3 and P2X2/3 receptor antagonist. Rapid application of ATP (20 microM) induced a fast inactivating current in colon-specific DRG neurons from both control and AA-treated rats. There was a twofold increase in the peak ATP responses in neurons from AA-treated rats. These currents were sensitive to TNP-ATP (100 nM). Under current-clamped conditions, ATP evoked a larger membrane depolarisation in neurons from neonatal AA-treated rats than in controls. P2X3R protein expression was significantly enhanced in colon-specific DRGs 8 weeks after neonatal AA treatment.. These data suggest that the large enhancement of P2XR expression and function may contribute to the maintenance of visceral hypersensitivity, thus identifying a specific neurobiological target for the treatment of chronic visceral hyperalgesia.

Topics: Acetic Acid; Adenosine Triphosphate; Animals; Chronic Disease; Colon; Disease Models, Animal; Hyperalgesia; Irritable Bowel Syndrome; Membrane Potentials; Neurons; Patch-Clamp Techniques; Purinergic P2 Receptor Antagonists; Rats; Rats, Sprague-Dawley; Receptors, Purinergic P2; Receptors, Purinergic P2X; Signal Transduction; Up-Regulation