Interaction between cannabinoid CB1 receptors and endogenous ATP in the control of spontaneous mechanical activity in mouse ileum

Background and purpose: Although it is well accepted that cannabinoids modulate intestinal motility by reducing cholinergic neurotransmission mediated by CB1 receptors, it is not known whether the endocannabinoids are involved in more complex circuits and if they interact with other systems. The aim of the present study was to examine possible interactions between cannabinoid CB1 receptors and purines in the control of spontaneous contractility of longitudinal muscle in mouse ileum. Experimental approach: The mechanical activity of longitudinally oriented ileal segments from mice was recorded as isometric contractions. Key results: The selective CB1 receptor agonist, N-(2-chloroethyl)5,8,11,14-eicosaetraenamide (ACEA) reduced, concentration dependently, spontaneous contractions in mouse ileum. This effect was almost abolished by tetrodotoxin (TTX)or atropine. Inhibition by ACEA was not affected by theophylline (P1 receptor antagonist) or by P2Y receptor desensitization with adenosine 5'[beta-thio]diphosphate trilithium salt, but was significantly reversed by pyridoxal phosphate-6-azo(benzene-2,4-disulphonic acid) (P2 receptor antagonist), by P2X receptor desensitization with alpha, beta-methyleneadenosine 5'-triphosphate lithium salt (alpha, beta-MeATP) or by 8,8'-[carbonylbis(imino-4,1-phenylenecarbonylimino-4,1-phenylenecarbonylimino)bis(1,3,5-naphthalenetrisulphonic acid)] (P2X receptor antagonist). Contractile responses to alpha, beta-MeATP (P2X receptor agonist) were virtually abolished by TTX or atropine, suggesting that they were mediated by acetylcholine released from neurones, and significantly reduced by ACEA. Conclusion and implications: In mouse ileum, activation of CB1 receptors, apart from reducing acetylcholine release from cholinergic nerves, was able to modulate negatively, endogenous purinergic effects, mediated by P2X receptors, on cholinergic neurons. Our study provides evidence for a role of cannabinoids in the modulation of interneuronal purinergic transmission. British Journal of Pharmacology (2009) 158, 243-251; doi:10.1111/j.1476-5381.2009.00260.x; published online 21 May 2009