Inverse gradient of nitrergic and purinergic inhibitory cotransmission in the mouse colon N. Ma~ n e, 1 R. Viais, 2 M. Martınez-Cutillas, 1 D. Gallego, 1,3 P. Correia-de-S a 2 and M. Jim enez 1,3 1 Department of Cell Biology, Physiology and Immunology and Neuroscience Institute, Universitat Autonoma de Barcelona, Barcelona, Spain 2 Center for Drug Discovery and Innovative Medicines (MedInUP), Instituto de Ci^encias Biomedicas Abel Salazar da Universidade do Porto (ICBAS-UP), Porto, Portugal 3 Centro de Investigacion Biomedica en Red de Enfermedades Hepaticas y Digestivas (CIBERehd), Instituto de Salud Carlos III, Barcelona, Spain Received 8 June 2015, revision requested 9 July 2015, revision received 1 September 2015, accepted 2 September 2015 Correspondence: M. Jimenez, VMD, PhD, Department of Cell Biology, Physiology and Immunology, Edifici V, Universitat Aut onoma de Barcelona 08193 Bellaterra, Cerdanyola del Valles, Spain. E-mail: marcel.jimenez@uab.es NM and RV are co-authors and equally contributed to this work. Abstract Aim: Gastrointestinal smooth muscle relaxation is accomplished by the neural corelease of ATP or a related purine and nitric oxide. Contractions are triggered by acetylcholine and tachykinins. The aim of this work was to study whether regional differences in neurotransmission could partially explain the varied physiological roles of each colonic area. Methods: We used electrophysiological and myography techniques to evaluate purinergic (L-NNA 1 mM incubated tissue), nitrergic (MRS2500 0.3 lM incubated tissue) and cholinergic neurotransmission (L-NNA 1 mM and MRS2500 0.3 lM incubated tissue) in the proximal, mid and distal colon of CD1 mice (n = 42). Results: Purinergic electrophysiological responses elicited by single pulses (28 V) were greater in the distal (IJPf MAX = 35.3  2.2 mV), followed by the mid (IJPf MAX = 30.6  1.0 mV) and proximal (IJPf MAX = 11.7  1.1 mV) colon. In contrast, nitrergic responses decreased from the proximal colon (IJPs MAX = 11.4  1.1 mV) to the mid (IJPs MAX = 9.1  0.4 mV), followed by the distal colon (IJPs MAX = 1.8  0.3 mV). A similar rank of order was observed in neural mediated inhibitory mechanical responses including electrical field stimulation- mediated responses and neural tone. ADPbs concentration–response curve was shifted to the left in the distal colon. In contrast, NaNP responses did not differ between regions. Cholinergic neurotransmission elicited contrac- tions of a similar amplitude throughout the colon. Conclusion: An inverse gradient of purinergic and nitrergic neurotrans- mission exists through the mouse colon. The proximal and mid colon have a predominant nitrergic neurotransmission probably due to the fact that their storage function requires sustained relaxations. The distal colon, in contrast, has mainly purinergic neurotransmission responsible for the pha- sic relaxations needed to propel dehydrated faeces. Keywords colonic relaxation, nitric oxide, purines, regional differences. Nerve-mediated smooth muscle contraction and relax- ation are needed to accomplish several colonic motor functions such as absorption, mixing, storage and propulsion. Although excitatory enteric neurones corelease other transmitters such as tachykinins (Hol- zer & Holzer-Petsche 1997), acetylcholine (Ach) is believed to be functionally predominant in inducing contractions in the gut (Goyal & Hirano 1996, © 2015 Scandinavian Physiological Society. Published by John Wiley & Sons Ltd, doi: 10.1111/apha.12599 120 Acta Physiol 2016, 216, 120–131