Control of enteric neuromuscular functions by purinergic A₃ receptors in normal rat distal colon and experimental bowel inflammation

Abstract

BACKGROUND AND PURPOSEAdenosine A3 receptors mediate beneficial effects in experimental colitis, but their involvement in enteric neuromuscular functions during bowel inflammation is undetermined. This study investigated the regulatory role of A3 receptors on colonic motility in the presence of experimental colitis. EXPERIMENTAL APPROACHColitis was induced in rats by 2,4-dinitrobenzenesulfonic acid. A3 receptors and adenosine deaminase (ADA, adenosine catabolic enzyme) mRNA were examined by RT-PCR. Tissue distribution of A3 receptors was detected by confocal immunofluorescence. The effects of 2,3-ethyl-4,5-dipropyl-6-phenylpyridine-3-thiocarboxylate-5-carboxylate (MRS1523) (MRS, A3 receptor antagonist), 2-chloro-N6-(3-iodobenzyl)-adenosine-5′-N-methyluronamide (2Cl-IB-MECA) (CIB, A3 receptor agonist), dipyridamole (DIP, adenosine transport inhibitor) and ADA were assayed on contractile responses evoked by electrical stimulation (ES) or carbachol in colonic longitudinal muscle preparations (LMP). KEY RESULTSRT-PCR showed A3 receptors and ADA mRNA in normal colon and their increased level in inflamed tissues. Immunofluorescence showed a predominant distribution of A3 receptors in normal myenteric ganglia and an increased density during colitis. MRS enhanced ES-induced cholinergic contractions in normal LMP, but was less effective in inflamed tissues. After pretreatment with dipyridamole plus ADA, to reduce extracellular adenosine, CIB decreased cholinergic motor responses of normal LMP to ES, with enhanced efficacy in inflamed LMP. A3 receptor ligands did not affect carbachol-induced contractions in LMP from normal or inflamed colon. CONCLUSIONS AND IMPLICATIONSNormally, adenosine modulated colonic cholinergic motility via activation of A3 receptors in the myenteric plexus. A3 receptor-mediated tonic inhibitory control by adenosine was impaired in inflamed bowel, despite increased density of functioning and pharmacologically recruitable A3 receptors. Abbreviations

The A3Adenosine Receptor: History and Perspectives

“…In enteric neurons and epithelial cells, the A 3 AR was first evidenced by immunohistochemical studies (Christofi et al, 2001;Antonioli et al, 2010;Ren et al, 2011) and subsequently quantified in colonic mucosa by radioligand binding experiments (Gessi et al, 2004a). The presence of functional A 3 AR has also been demonstrated in human lung parenchyma, in lung type 2 alveolar-like cells (A549), and in bronchi through radioligand binding and immunohistochemical assays Calzetta et al, 2011).…”

“…A 3 ARs are present in immune cells and are involved in the physiopathologic regulation of inflammatory and immune processes mediated by adenosine (Antonioli et al, 2010;Hasko and Cronstein, 2013).…”

Potential for Developing Purinergic Drugs for Gastrointestinal Diseases

“…Neural A 3 AR are involved in the regulation of both neuromuscular functions 145 and coordination of motility and secretion in the colon. 146 A 3 AR is distributed throughout myenteric ganglia in the colon, with highest expression in distal colon of the rat.…”

“…RT-PCR indicated that A 3 and ADA mRNA increased in inflamed tissues from experimental colitis. 145 The A 3 AR – mediated tonic inhibitory control of colonic cholinergic contractions was shown to be impaired in the inflamed bowel despite an increase in functional A 3 AR.…”

Effects of Inflammation on the Innervation of the Colon

“…Purinergic neuromuscular transmission to the vascular and circular smooth muscle is reduced during experimental colitis in mice and rats (Antonioli et al 2010;Neshat et al 2009;Roberts et al 2012). ACh released from submucosal vasomotor neurons binds to endothelial muscarinic receptors, which stimulates endothelial NO synthase.…”