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

• Published in: The Journal of physiology 2012-04, Vol.590 (8), p.1943-1956
• Main Authors: Gallego, Diana, Gil, Víctor, Martínez‐Cutillas, Míriam, Mañé, Noemí, Martín, Maria Teresa, Jiménez, Marcel
• Format: Article
• Language: English
• Subjects: Adenine; Alimentary; Animal models; ATP; Colon; Gastrointestinal tract; Hyperpolarization; Membrane potential; Microelectrodes; Motility; Motor neurons; Muscle contraction; Neuromuscular junctions; Neurotransmission; Neurotransmitters; Nitric oxide; Nitroarginine; Purine P2Y receptors; purines; Smooth muscle
• ISSN: 0022-3751; 1469-7793
• DOI: 10.1113/jphysiol.2011.224345

Key points  •  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. •  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. •  In the present study we used a genetically modified mouse in which P2Y1 receptors had been knocked out. •  P2Y1‐deficient mice had functional nitrergic neurotransmission but purinergic neurotransmission was absent. •  The present work confirms the hypothesis demonstrating that P2Y1 receptors mediate the purinergic component of the smooth muscle relaxation in the gastrointestinal tract.   Purinergic and nitrergic co‐transmission is the dominant mechanism responsible for neural‐mediated smooth muscle relaxation in the gastrointestinal tract. The aim of the present paper was to test whether or not P2Y1 receptors are involved in purinergic neurotransmission using P2Y1−/− knock‐out mice. Tension and microelectrode recordings were performed on colonic strips. In wild type (WT) animals, electrical field stimulation (EFS) caused an inhibitory junction potential (IJP) that consisted of a fast IJP (MRS2500 sensitive, 1 μm) followed by a sustained IJP (Nω‐nitro‐l‐arginine (l‐NNA) sensitive, 1 mm). The fast component of the IJP was absent in P2Y1−/− mice whereas the sustained IJP (l‐NNA sensitive) was recorded. In WT animals, EFS‐induced inhibition of spontaneous motility was blocked by the consecutive addition of l‐NNA and MRS2500. In P2Y1−/− mice, EFS responses were completely blocked by l‐NNA. In WT and P2Y1−/− animals, l‐NNA induced a smooth muscle depolarization but ‘spontaneous’ IJP (MRS2500 sensitive) could be recorded in WT but not in P2Y1−/− animals. Finally, in WT animals, 1 μm MRS2365 caused a smooth muscle hyperpolarization that was blocked by 1 μm MRS2500. In contrast, 1 μm MRS2365 did not modify smooth muscle resting membrane potential in P2Y1−/− mice. β‐Nicotinamide adenine dinucleotide (β‐NAD, 1 mm) partially mimicked the effect of MRS2365. We conclude that P2Y1 receptors mediate purinergic neurotransmission in the gastrointestinal tract and β‐NAD partially fulfils the criteria to participate in rodent purinergic neurotransmission. The P2Y1−/− mouse is a useful animal model to st