P-2-PURINOCEPTORS ON POSTGANGLIONIC SYMPATHETIC NEURONS

1 Postganglionic sympathetic neurones possess both excitatory and inhi bitory P-2-purinoceptors. 2 The mechanisms of action of excitatory P-2 -purinoceptors have recently been studied on cultured sympathetic neur ones of the rat. The receptors mediate fast increases in intracellular Ca2+ levels and a release of noradrenaline. They are likely to belong to the neuronal types of P-2X- purinoceptors and to he located on the sympathetic nerve cell bodies or their dendrites. 3 Inhibitory P-2-pu rinoceptors have been shown to operate at sympathetic axon terminals i n isolated tissues. Adenine nucleotides decreased the stimulation-evok ed release of noradrenaline by activation of these receptors. The rece ptors are likely to belong to the group of G-protein-coupled P-2Y-puri noceptors. They mediate a negative feedback in which co-transmitter AT P inhibits subsequent sympathetic transmitter release.