Local regulation of [3H]-noradrenaline release from the isolated guinea-pig right atrium by P2X-receptors located on axon terminals

Abstract

1 In this study the regulation of cardiac sympathetic outflow by presynaptic P2X receptor-gated ion channels was examined. 2 ATP (30 μM-1 mM) and other P2-receptor agonists elicited [3H]-noradrenaline ([3H]-NA) outflow from the isolated guinea-pig right atrium with the potency order of ATP>2-methylthioATP> α,β-methylene-ATP=ADP, whereas β,γ-methylene-L-ATP was inactive. 3 Ca2+-free conditions abolished both electrical field stimulation (EFS)- and ATP-evoked release of tritium. Unlike from EFS-induced outflow, ATP-induced [3H]-NA outflow was not reduced by ωConotoxin-GVIA (100 nM), Cd2+ (100 μM) and tetrodotoxin (1 μM). 4 The rapid extracellular decomposition of ATP was revealed by HPLC analysis. However, the effect of ATP to promote [3H]-NA release was not prevented by 8-cyclopentyl-1,3-dipropylxanthine (DPCPX, 250 nM), 3,7-dimethyl-1-propargylxanthine (DMPX, 250 nM), or by reactive blue 2 (RB2, 10 μM), antagonists of A1-, A2- and inhibitory P2 receptors. 5 Zn2+ (50 μM), the P2X-receptor modulator potentiated, and P2X receptor antagonists, i.e. suramin (300μM), pyridoxal-phosphate-6-azophenyl-2′,4′-disulphonicacid (PPADS, 30 μM) and 2′-o(trinitrophenyl)-adenosine 5′-triphosphate (TNP-ATP, 30 μM) antagonized the ATP (1 mM)-evoked response. 6 RT-PCR study revealed the expression of P2X2 and P2X3 receptor mRNAs in guinea-pig superior cervical ganglion. 7 PPADS (30 μM) significantly reduced the EFS-induced [3H]-NA outflow in the presence DPCPX (250 nM) and RB2 (10 μM). 8 In summary a P2X-type purinoceptor regulates noradrenaline release from the isolated right atrium of the guinea-pig. The pharmacological profile of the receptor resemble to homo-oligomeric P2X3 or hetero-oligomeric P2X2/P2X3 complexes, and provide a new target to intervene on sympathetic neuroeffector transmission at the presynaptic site.