title: Purinergic and nitrergic neuromuscular transmission mediates spontaneous neuronal activity in the rat colon.
abstract: Nitric oxide (NO) and ATP mediate smooth muscle relaxation in the gastrointestinal tract. However, the involvement of these neurotransmitters in spontaneous neuronal activity is unknown. The aim of the present work was to study spontaneous neuromuscular transmission in the rat midcolon. Microelectrode experiments were performed under constant stretch both in circular and longitudinal directions. Spontaneous inhibitory junction potentials (sIJP) were recorded. Tetrodotoxin (1 microM) and apamin (1 microM) depolarized smooth muscle cells and inhibited sIJP. N(omega)-nitro-l-arginine (l-NNA, 1 mM) depolarized smooth muscle cells but did not modify sIJP. In contrast, the P2Y(1) antagonist MRS-2500 (1 microM) did not modify the resting membrane potential (RMP) but reduced sIJP (IC(50) = 3.1 nM). Hexamethonium (200 microM), NF-023 (10 microM), and ondansetron (1 microM) did not modify RMP and sIJP. These results correlate with in vitro (muscle bath) and in vivo (strain gauges) data where l-NNA but not MRS-2500 induced a sustained increase of spontaneous motility. We concluded that, in the rat colon, inhibitory neurons regulate smooth muscle RMP and cause sIJP. In vitro, the release of inhibitory neurotransmitters is independent of nicotinic, P2X, and 5-hydroxytryptamine type 3 receptors. Neuronal NO causes a sustained smooth muscle hyperpolarization that is responsible for a constant inhibition of spontaneous motility. In contrast, ATP acting on P2Y(1) receptors is responsible for sIJP but does not mediate inhibitory neural tone. ATP and NO have complementary physiological functions in the regulation of gastrointestinal motility.
authors.affiliation: Department of Cell Biology, Physiology and Immunology, Universitat Autònoma de Barcelona, 08193 Bellaterra, Barcelona, Spain.
authors.forename: Víctor
authors.initials: V
authors.lastname: Gil
authors.forename: Diana
authors.initials: D
authors.lastname: Gallego
authors.forename: Laura
authors.initials: L
authors.lastname: Grasa
authors.forename: María Teresa
authors.initials: MT
authors.lastname: Martín
authors.forename: Marcel
authors.initials: M
authors.lastname: Jiménez
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism*; D000779:Anesthetics, Local / Q000494:pharmacology; D000818:Animals; D003106:Colon / Q000294:innervation*; D003838:Deoxyadenine Nucleotides / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005769:Gastrointestinal Motility / Q000187:drug effects; D053444:Inhibitory Postsynaptic Potentials; D008297:Male; D009126:Muscle Relaxation / Q000187:drug effects; D009130:Muscle, Smooth / Q000294:innervation*; D009197:Myenteric Plexus / Q000187:drug effects / Q000378:metabolism*; D009433:Neural Inhibition; D018733:Nicotinic Antagonists / Q000494:pharmacology; D026602:Nitrergic Neurons / Q000378:metabolism*; D009569:Nitric Oxide / Q000378:metabolism*; D019001:Nitric Oxide Synthase / Q000037:antagonists & inhibitors / Q000378:metabolism; D052248:Nitric Oxide Synthase Type I; D019335:Nitroarginine / Q000494:pharmacology; D026902:Potassium Channel Blockers / Q000494:pharmacology; D058919:Purinergic P2 Receptor Antagonists; D051381:Rats; D017207:Rats, Sprague-Dawley; D018048:Receptors, Purinergic P2 / Q000378:metabolism; D058472:Receptors, Purinergic P2Y1; D044406:Receptors, Serotonin, 5-HT3 / Q000378:metabolism; D058831:Serotonin 5-HT3 Receptor Antagonists; D012702:Serotonin Antagonists / Q000494:pharmacology
chemical_list: C495475:2-iodo-N(6)-methyl-(N)-methanocarba-2'-deoxyadenosine-3',5'-bisphosphate; D000779:Anesthetics, Local; D003838:Deoxyadenine Nucleotides; D004791:Enzyme Inhibitors; D018733:Nicotinic Antagonists; C546384:P2ry1 protein, rat; D026902:Potassium Channel Blockers; D058919:Purinergic P2 Receptor Antagonists; D018048:Receptors, Purinergic P2; D058472:Receptors, Purinergic P2Y1; D044406:Receptors, Serotonin, 5-HT3; D058831:Serotonin 5-HT3 Receptor Antagonists; D012702:Serotonin Antagonists; D019335:Nitroarginine; D009569:Nitric Oxide; D000255:Adenosine Triphosphate; D019001:Nitric Oxide Synthase; D052248:Nitric Oxide Synthase Type I; C496322:Nos1 protein, rat