D. Gallego

Purinergic neuromuscular transmission is absent in the colon of P2Y1 knocked out mice

Key pointsu2002 •u2002 Neural‐mediated relaxation occurs in the gastrointestinal tract. To accomplish this function, two neurotransmitters, ATP or a related purine and nitric oxide, are released by inhibitory motorneurons. •u2002 The type of purinergic receptor is still under debate but previous data using a classical pharmacological approach (receptor agonists and antagonists) suggested that P2Y1 receptors are responsible for purinergic neurotransmission in the gastrointestinal tract. •u2002 In the present study we used a genetically modified mouse in which P2Y1 receptors had been knocked out. •u2002 P2Y1‐deficient mice had functional nitrergic neurotransmission but purinergic neurotransmission was absent. •u2002 The present work confirms the hypothesis demonstrating that P2Y1 receptors mediate the purinergic component of the smooth muscle relaxation in the gastrointestinal tract.

Pharmacological characterization of purinergic inhibitory neuromuscular transmission in the human colon

Backgroundu2002 In the present study, we further characterize the purinergic receptors mediating the inhibitory junction potential (IJP) and smooth muscle relaxation in the human colon using a new, potent and selective agonist (MRS2365), and antagonists (MR2279 and MRS2500) of the P2Y1 receptor. The P2Y12 antagonist AR‐C66096 was tested as well. Using this pharmacological approach, we tested whether β‐nicotinamide adenine dinucleotide (β‐NAD) fulfilled the criteria to be considered an inhibitory neurotransmitter in the human colon.

Effects of inhibitors of hydrogen sulphide synthesis on rat colonic motility

BACKGROUND AND PURPOSE The role of hydrogen sulphide (H2S) as a putative endogenous signalling molecule in the gastrointestinal tract has not yet been established. We investigated the effect of D,L‐propargylglycine (PAG), an inhibitor of cystathionine γ‐lyase (CSE), amino‐oxyacetic acid (AOAA) and hydroxylamine (HA), inhibitors of cystathionine β‐synthase (CBS) on rat colonic motility.

P2Y(1) knockout mice lack purinergic neuromuscular transmission in the antrum and cecum.

Backgroundu2002 Pharmacological studies using selective P2Y1 antagonists, such as MRS2500, and studies with P2Y1−/− knockout mice have demonstrated that purinergic neuromuscular transmission is mediated by P2Y1 receptors in the colon. The aim of the present study was to test whether P2Y1 receptors are involved in purinergic neurotransmission in the antrum and cecum.

Specific and complementary roles for nitric oxide and ATP in the inhibitory motor pathways to rat internal anal sphincter

Backgroundu2002 The neurotransmitters mediating inhibitory pathways to internal anal sphincter (IAS) have not been fully characterized. Our aim was to assess the putative release of nitric oxide, purines and vasoactive intestinal peptide (VIP) from inhibitory motor neurons (MNs) and their role in the myogenic tone, resting membrane potential (RMP) of smooth muscle cells (SMC), spontaneous inhibitory junction potentials (sIJP), mechanical relaxation, and IJP induced by electrical field stimulation (EFS) or nicotine.

Effects of hydrogen sulphide on motility patterns in the rat colon

Hydrogen sulphide (H2S) is an endogenous gaseous signalling molecule with putative functions in gastrointestinal motility regulation. Characterization of H2S effects on colonic motility is crucial to establish its potential use as therapeutic agent in the treatment of colonic disorders.

Potential role of the gaseous mediator hydrogen sulphide (H2S) in inhibition of human colonic contractility.

BACKGROUNDnHydrogen sulphide (H2S) is an endogenous signalling molecule that might play a physiologically relevant role in gastrointestinal motility. Cystathionine β-synthase (CBS) and cystathionine γ-lyase (CSE) are two enzymes responsible for H2S production. d,l-Propargylglycine (PAG) is a CSE inhibitor whereas both aminooxyacetic acid (AOAA) and hydroxylamine (HA) are CBS inhibitors. The characterization of H2S responses and its mechanism of action are crucial to define H2S function.nnnMETHODSnHuman colonic strips were used to investigate the role of H2S on contractility (muscle bath) and smooth muscle electrophysiology (microelectrodes). NaHS was used as a H2S donor.nnnRESULTSnCombination of PAG and AOAA depolarized the smooth muscle (5-6mV, n=4) and elicited a transient increase in tone (260.5±92.8mg, n=12). No effect was observed on neural mediated inhibitory junction potential or relaxation. In the presence of tetrodotoxin 1μM, NaHS concentration-dependently inhibited spontaneous contractions (EC50=329.2μM, n=18). This effect was partially reduced by the guanylyl cyclase inhibitor ODQ 10μM (EC50=2.6μM, n=12) and by l-NNA 1mM (EC50=1.4mM, n=8). NaHS reversibly blocked neural mediated cholinergic (EC50=2mM) and tachykinergic (EC50=5.7mM) contractions. NaHS concentration-dependently reduced the increase in spontaneous mechanical activity (AUC) induced by carbachol (EC50=1.9mM) and NKA (EC50=1.7mM AUC).nnnCONCLUSIONSnH2S might be an endogenous gasomediator regulating human colonic contractility. Its inhibitory effect is observed at high concentrations and could be mediated by a direct effect on smooth muscle with a possible synergistic effect with NO, as well as by an interaction with the cholinergic and tachykinergic neural mediated pathways.

Differential functional role of purinergic and nitrergic inhibitory cotransmitters in human colonic relaxation

ATP and nitric oxide (NO) are released from enteric inhibitory motor neurones and are responsible for colonic smooth muscle relaxation. However, how frequency of neural stimulation affects this cotransmission process and the post‐junctional responses has not been systematically characterized in the human colon.

Nitrergic neuro-muscular transmission is up-regulated in patients with diverticulosis.

Neuro‐transmission impairment could be associated to motility changes observed in patients with diverticular disease. Therefore, the objective was to characterize the inhibitory neuro‐muscular transmission and gene expression changes of the enteric inhibitory pathways in patients with diverticulosis (DS).

EP2 and EP4 receptors mediate PGE2 induced relaxation in murine colonic circular muscle: pharmacological characterization.

BACKGROUNDnProstaglandin E2 (PGE2) is a regulator of gastrointestinal motility that might be involved in impaired motor function associated to gut inflammation. The aim of the present work is to pharmacologically characterize responses to exogenous and endogenous PGE2 in the mouse colon targeting EP2 and EP4 receptors.nnnMETHODSnWild type (WT) and EP2 receptor knockout (EP2-KO) mice were used to characterize PGE2 and butaprost (EP2 receptor agonist) effects on smooth muscle resting membrane potential and myogenic contractility in circularly oriented colonic preparations.nnnRESULTSnIn WT animals, PGE2 and butaprost concentration-dependently inhibited spontaneous contractions and hyperpolarized smooth muscle cells. Combination of both EP2 (PF-04418948 0.1μM) and EP4 receptor antagonists (L-161,982 10μM) was needed to block both electrical and mechanical PGE2 responses. Butaprost inhibitory responses (both electrical and mechanical) were totally abolished by PF-04418948 0.1μM. In EP2-KO mice, PGE2 (but not butaprost) concentration-dependently inhibited spontaneous contractions and hyperpolarized smooth muscle cells. In EP2-KO mice, PGE2 inhibition of spontaneous contractility and hyperpolarization was fully antagonized by L-161,982 10μM. In WT animals, EP2 and EP4 receptor antagonists caused a smooth muscle depolarization and an increase in spontaneous mechanical activity.nnnCONCLUSIONSnPGE2 responses in murine circular colonic layer are mediated by post-junctional EP2 and EP4 receptors. PF-04418948 and L-161,982 are selective EP2 and EP4 receptor antagonists that inhibit PGE2 responses. These antagonists might be useful pharmacological tools to limit prostaglandin effects associated to dismotility in gut inflammatory processes.