Evidence for P₂‐purinoceptor‐mediated inhibition of noradrenaline release in rat brain cortex

Abstract

1 Some postganglionic sympathetic axons possess P2Y-like P2-purinoceptors which, when activated, decrease the release of noradrenaline. We examined the question of whether such receptors also occur at the noradrenergic axons in the rat brain cortex. Slices of the brain cortex were preincubated with pH]-noradrenaline, then superfused with medium containing desipramine (1 gM) and stimulated electrically, in most experiments by trains of 4 pulses/100 Hz.2 The selective adenosine Al-receptor agonist, N6-cyclopentyl-adenosine (CPA; 0.03-3 gM) as well as the non-subtype-selective agonist 5'-N-ethylcarboxamido-adenosine (NECA; 0.3-3 EM) reduced the evoked overflow of tritium, whereas the adenosine A2.-receptor agonist, 2-p-(2-carbonylethyl)-phenethylamino-5'-N-ethylcarboxamido-adenosine (CGS-21680; 0.003-30;LM) and the adenosine A3-receptor agonist N6-2-(4-aminophenyl)ethyl-adenosine (APNEA; 0.03-31M) caused no change. Of the nucleotides tested, ATP (30-300 JM), adenosine-5'-O-(3-thiotriphosphate) (ATPyS; 30-300 pM), adenosine-5'-O-(2-thiodiphosphate) (ADPPS; 30-300ILM), P1,P4-di(adenosine-5')-tetraphosphate (Ap4A; 30-3001LM) and the preferential P2Y-purinoceptor agonist, 2-methylthio-ATP (300 tM) decreased the evoked overflow of tritium. The P' -purinoceptor agonist, a,-methylene-ATP (3-3001fM) caused no change.3 The Al-selective antagonist, 8-cyclopentyl-1,3-dipropylxanthine (DPCPX; 10 nM) attenuated the effects of the nucleosides CPA (apparent pKB value 9.8) and NECA as well as of the nucleotides ATP (apparent pKB 9.3), ATPyS (apparent pKB 9.2) and ADPBS (apparent pKB 8.7). CGS-21680 and APNEA were ineffective also in the presence of DPCPX. The A2-selective antagonist 1,3-dipropyl-8-(3,4-dimethoxystyryl)-7-methylxanthine (KF-17837) reduced the effects of CPA, NECA and ATPyS only when given at a concentration of 300 nM but not at 1O nM. 4 The P2-purinoceptor antagonists, suramin (300 ,M), reactive blue 2 (30 1M) and cibacron blue 3GA (301M) did not change the effect of CPA. Suramin and cibacron blue 3GA shifted the concentrationresponse curve of ATPyS to the right (apparent pKB values 3.7 and 5.0, respectively). Reactive blue 2 also attenuated the effect of ATPyS, and cibacron blue 3GA attenuated the effect of ATP, but in these cases the agonist concentration-response curves were not shifted to the right. There was no antagonistic effect of suramin against ATP and ADPPS. 5 The results indicate that rat cerebrocortical noradrenergic axons possess, in addition to the known adenosine Al-receptor, a separate purinoceptor for nucleotides (P2) which, in contrast to the Al-receptor, is blocked by suramin, reactive blue 2 and cibacron blue 3GA. Nucleotides such as ATP and ATPyS activate both receptors. Inconsistencies in antagonist effects against nucleotides are probably due to this activation of two receptors. The presynaptic P2-purinoceptor is P2Y-like, as it is in the peripheral sympathetic nervous system. Keywords: Rat brain cortex; PI-purinoceptor; P2-purinoceptor; presynaptic purinoceptors; noradrenaline release; ad...

Functional characterization of adenosine receptors in the nucleus tractus solitarius mediating hypotensive responses in the rat

“…However, a similar result was reported by von Kugelgen et al (1994), who found that high concentrations of APNEA had no effect on adenosine Al receptors in the rat brain cortex.…”

Purinergic modulation of norepinephrine release and uptake in rat brain cortex: contribution of glial cells

“…The superficial slice was discarded, and round slices of 400 m (Microtome Leica VT1000S, Nussloch, Germany) were incubated for 45 min in a warmed (37°C) and gassed (95% O 2 -5% CO 2 ) Krebs solution with the following composition (mM): 118 NaCl, 4.7 KCl, 2. (von Kügelgen et al 1994). Briefly, occipital-parietal cortical brain slices were incubated in 2 ml of Krebs solution containing 0.1 M [ 3 H]NE (specific activity of 1.65 TBq/mmol) for 15 min.…”

“…The purinergic receptors, in particular the P2Y receptors, which include eight subtypes, P2Y 1,2,4,6,11,12,13,14 (Abbracchio et al 2006), have also been shown to play a relevant role in the regulation of synaptic transmission in several brain regions (Gonçalves and Queiroz 2008;Sperlágh et al 2007), participating in the modulation of neuronal transmitter release. Cortical norepinephrine release evoked by electrical stimulation was shown to be modulated by P2Y receptors (von Kügelgen et al 1994), but the subtypes of P2Y receptors have not been identified.…”

ATP as a presynaptic modulator

“…Thus, it has been reported that P2Y-like receptor activation inhibits noradrenaline release from rat cerebral cortical [126] and hippocampal slices [145], and there is a hint that P2X receptor activation may facilitate noradrenaline release in the rabbit cerebral cortex [130].…”

“…epj, excitatory junction potential; epp, endplate potential; epsc, excitatory postsynaptic current; mepp, mini epp; NMJ, neuromuscular junction; sepp, spontaneous epp; NT, neurotransmitter. studies showed that ATP [124] and ATP analogues inhibit the evoked release of noradrenaline, but it was not clear if this action involves the activation of either P2Y-like receptors [125][126][127][128][129], adenosine A 1 receptors [130] or a proposed mixed ATP/adenosine receptor, named P3 receptor [55][56][57]131]. Other studies (Table 1) showed that activation of P2-like receptors facilitates evoked release of noradrenaline, and this action was proposed to involve either 'atypical' P2Y-like receptors [132,133] or P2X receptors [121].…”