Adenosine 2B receptors (A_2BAR) on enteric neurons regulate murine distal colonic motility

Abstract

Delayed colonic emptying leading to constipation is a significant health concern. We investigated the role of adenosine 2B receptor (A(2B)AR) in modulating distal colonic motility using wild-type and A(2B)AR-knockout (A(2B)AR(-/-)) mice. Colon motility was assessed using stool characteristics and colonic transit. Distal colonic ganglia, isolated by laser capture microdissection, were tested for A(2B)AR expression by RT-PCR. The distal colon contraction and relaxation responses were assessed by electrical field stimulation (EFS) in presence of A(2B)AR agonists, antagonists or inhibitors of nitric oxide (NO) and guanylate cyclase. Nitrite levels were measured in enteric neuronal cultures exposed to A(2B)AR agonists/antagonists. A(2B)AR(-/-) mice display increased stool retention, decreased stool frequency, delayed colonic emptying, and decreased circular muscle relaxation. RT-PCR identified A(2B)AR expression in distal colonic ganglia. EFS studies revealed that enteric neuronal A(2B)AR is essential for distal colonic relaxation, and A(2B)AR antagonists can inhibit relaxation. Enteric neurons stimulated with A(2B)AR agonists produced more nitrite than cultures treated with antagonists. We demonstrate an essential role of A(2B)AR in regulating distal colon relaxation, as A(2B)AR activation is linked to NO signaling. Hence targeting the colonic A(2B)AR could represent a novel therapeutic strategy to treat constipation.

Tumor Necrosis Factor–Neuropeptide Y Cross Talk Regulates Inflammation, Epithelial Barrier Functions, and Colonic Motility

“…The cleaved caspase-3 staining (1: 300) was expressed as a percentage of peripherin staining. The images were captured using a Zeiss fluorescence microscope, and analyzed by Metamorph (Molecular Devices, Silicon Valley, CA, USA) as described previously (17). …”

“…Enteric ganglia were captured from cryo sections by LCM as described previously (17). The RNA was isolated from the ganglia using Arcturus Pico-Pure RNA Extraction Kit (Grand Island, NY) and amplified for NPY expression by real time PCR.…”

Novel functional roles for enteric glia in the gastrointestinal tract

“…13,28,[38][39][40][41][42][43][44][45][46] Importantly, at least some of these glial receptors are functional in situ and elicit glial activity in the form of increasing intracellular calcium responses 38,42,47 or elevating cyclic AMP. 48,49 Purines are the most ubiquitous mediators of enteric neuron-to-glia communication, and activating enteric nerves elicits ATP release and subsequent activation of glial P2 receptors in multiple experimental paradigms. [40][41][42]47 This finding might not be particularly surprising given that all neurons have the capacity to release ATP 50 and enteric glia are highly responsive to purines.…”

Activation of adenosine low-affinity A3 receptors inhibits the enteric short interplexus neural circuit triggered by histamine

“…We did not test whether our agonists or antagonists also interact with A2 receptors and relied on their selectivity for A1 or A3 receptors as described earlier; their involvement in the inhibitory effects of A3 compounds on dimaprit-induced secretory responses is unlikely since activation of A2 receptors is known to stimulate Cl Ϫ secretion (14,18,55) and elicit slow membrane depolarization and excitation in enteric neurons (4,12,15). Some contribution of A2b-effects with A3 agonists and antagonists cannot be entirely ruled out (10). Studies in A3AR Ϫ/Ϫ knockout mice are planned (9).…”