653 Adenosine 2b (A2b)Receptor Knock Out Mice Have Impaired Colonic Motility

Abstract

Aim : Adenosine receptors play an important role in the motor and secretory functions of enteric nervous system. Aim of the present study was to understand the role of adenosine 2b receptor in the gastrointestinal motility. Methods: Distal colon from age matched wild type and Adenosine 2b receptor knock out mice(A2bR KO) were stained for NADPH diaphorase neurons and scored per unit area. Distal colonic motility was examined by the bead expulsion test. Neuronally-mediated colonic relaxation and contraction was assessed by isometric muscle recording in isolated circular muscle strips from the distal colon. The role of A2b receptor in inhibiting the contraction was assessed by the addition of adenosine receptor agonist, adenosine-5'-N-ethyl carboxamide (NECA, 10 μM). Results : : A2bR KO mice showed significant decrease in the number of NADPH Diaphorase positive neurons per unit area (12.2 ± 0.54) compared to WT mice (19.03 ± 0.52, p<0.001, n=3). Consistent with this loss of nitrergic neurons, colonic relaxation was significantly reduced in the distal colon of A2b KO mice (16.97 ± 4.9%)compared to the WT (54.01 ± 5.2%) mice. Loss of nitrergic neurons can contribute to delayed colonic emptying. Distal colonic emptying, assessed by bead test, was significantly delayed in the A2bR KO mice (8.4 ± 1.0 min) as compared to the WT mice (4.98 ± 0.6 min, p<0.001, n=6). Addition of NECA caused significant reduction in the amplitude of baseline as well as EFS induced contractions (n = 3, p <0.05) in the WT mice. This inhibitory effect of NECA was not seen in the A2b KO mice, indicating the role of A2b receptor in mediating inhibitory neurotransmission in the distal colon. Conclusions : These data suggest that A2b receptor in the distal colon has a role in enteric inhibitory neurotransmission and can impact GI motility. Targeting the A2b receptor might be of therapeutic interest in treating motility disorders.