CULTURED CHICK SYMPATHETIC NEURONS - ATP-INDUCED NORADRENALINE RELEASE AND ITS BLOCKADE BY NICOTINIC RECEPTOR ANTAGONISTS

The ATP-induced increase in tritium outflow from cultured chick sympathetic neurons prelabelled with [H-3]-noradrenaline was investigated. Seven days-old dissociated cell cultures of embryonic paravertebral ganglia, loaded with [H-3]-noradrenaline (0.05 mu M), were superfused in the presence of (+)-oxaprotiline and exposed to ATP, ATP-analogues, or 1,1-dimethyl-4-piperazinium (DMPP) for 2 min. ATP (3 mu M-3 mM), 2-methylthio-ATP (3-100 mu M), as well as DMPP (10 and 100 mu M) induced a significant overflow of tritium. The EC(50)-value of ATP was 20 mu M. Both the ATP-induced and the DMPP-induced tritium overflow was Ca2+-dependent and sensitive to tetrodotoxin (0.3 mu M) and omega-conotoxin (0.1 mu M); in addition, it was inhibited by the alpha(2)-adrenoceptor agonist 5-bromo-6-(2-imidazoline-2-ylamino)-quinoxaline (UK-14,304; 1 mu M). The effects of ATP and DMPP were not additive. The ATP-induced as well as the DMPP-induced overflow of tritium was diminished by the P-2-purinoceptor antagonists suramin (300 mu M) and reactive blue 2 (3 mu M); in all 4 cases, the inhibition amouted to approximately 40%. The tritium overflow induced by ATP or DMPP was almost abolished by the nicotinic receptor antagonist mecamylamine (10 mu M) and markedly inhibited by hexamethonium (100 mu M). Neither ATP nor electrical stimulation caused an overflow of tritium from cultures loaded with [H-3]-choline. The results suggest that ATP at mu molar concentrations induces noradrenaline release from cultured chick sympathetic neurons via an action on a subclass of the nicotinic cholinoceptor.