The P2Y1 and P2Y12 receptors mediate autoinhibition of transmitter release in sympathetic innervated tissues

In the sympathetic nervous system, ATP is a co-transmitter and modulator of transmitter release, inhibiting noradrenaline release by acting on P2Y autoreceptors, but in peripheral tissues the subtypes involved have only scarcely been identified. We investigated the identity of the noradrenaline release-inhibiting P2Y subtypes in the epididymal portion of vas deferens and tail artery of the rat. The subtypes operating as autoreceptors, the signalling mechanism and cross-talk with α2-autoreceptors, was also investigated in the epididymal portion.In both tissues, the nucleotides 2-methylthioATP, 2-methylthioADP, ADP and ATP inhibited noradrenaline release up to 68%, with the following order of potency: 2-methylthioADP = 2-methylthioATP > ADP = ATP in the epididymal portion and 2-methylthioADP = 2-methylthioATP = ADP > ATP in the tail artery. The selective P2Y1 antagonist 2′-deoxy-N6-methyladenosine 3′,5′-bisphosphate (30 μM) and the P2Y12 antagonist 2,2-dimethyl-propionic acid 3-(2-chloro-6-methylaminopurin-9-yl)-2-(2,2-dimethyl-propionyloxymethyl)-propyl ester (30 μM) increased noradrenaline release per se by 25 ± 8% and 18 ± 3%, respectively, in the epididymal portion but not in tail artery. Both antagonists attenuated the effect of nucleotides in the epididymal portion whereas in tail artery only the P2Y1 antagonist was effective. The agonist of P2Y1 and P2Y12 receptors, 2-methylthioADP, caused an inhibition of noradrenaline release that was not prevented by inhibition of phospholipase C or protein kinase C but was abolished by pertussis toxin. 2-methylthioADP and the adenosine A1 receptor agonist N6-cyclopentyladenosine were less potent at inhibiting noradrenaline release under marked influence of α2-autoinhibition.In both tissues, nucleotides modulate noradrenaline release by activation of inhibitory P2Y1 receptors but in the epididymal portion P2Y12 receptors also participate. P2Y1 and P2Y12 receptors are coupled to Gi/o-proteins and operate as autoreceptors in the vas deferens where they interact with α2-adrenoceptors on the modulation of noradrenaline release.