Short communicationThe effect of suramin on vasodilator responses to ATP and 2-methylthio-ATP in the Sprague-Dawley rat coronary vasculature
Abstract
The effect of suramin, a P2 purinoceptor antagonist, on the vasodilator response to adenosine 5′-triphosphate (ATP), 2-methylthio-ATP (2-meSATP) and adenosine were examined in the Sprague-Dawley rat coronary vasculature using the Langendorff heart preparation. Relaxation induced by 2-meSATP was significantly inhibited by suramin. Only responses to low doses of adenosine and ATP were inhibited bu suramin. 8-(p-Sulphophenyl)theophylline (8-PSPT) did not affect the relaxant response to ATP and 2-meSATP at a concentration that significantly inhibited the response to adenosine. It is concluded that 2-meSATP acts via P2Y purinoceptors while ATP appears to be acting largely through a different mechanism. It is not acting via a P1 purinoceptor because ATP was not inhibited by the P1 purinoceptor antagonist 8-PSPT.
References (10)
- C.M. Brown et al.
The structural conformation of the polyphosphate chain of the ATP molecule is critical for its promotion of prostaglandin biosynthesis
Eur. J. Pharmacol.
(1981) - A. Chinellato et al.
Pharmacological characterization of ATP receptors mediating vasodilation on isolated rabbit aorta
Gen. Pharmacol.
(1992) - A.M. Hopwood et al.
ATP mediates coronary vasoconstriction via P2X-purinoceptors and coronary vasodilatation via P2Y-purinoceptors in the isolated perfused rat heart
Eur. J. Pharmacol.
(1987) - S.E. O'Connor et al.
Further subclassification of ATP receptors based on agonist studies
Trends Pharmacol. Sci.
(1991) - G. Burnstock et al.
Purinergic receptors in the cardiovascular system
Prog. Pharmacol.
(1986)
Cited by (16)
Cellular distribution and functions of P2 receptor subtypes in different systems
2004, International Review of CytologyThis review is aimed at providing readers with a comprehensive reference article about the distribution and function of P2 receptors in all the organs, tissues, and cells in the body. Each section provides an account of the early history of purinergic signaling in the organ⧸cell up to 1994, then summarizes subsequent evidence for the presence of P2X and P2Y receptor subtype mRNA and proteins as well as functional data, all fully referenced. A section is included describing the plasticity of expression of P2 receptors during development and aging as well as in various pathophysiological conditions. Finally, there is some discussion of possible future developments in the purinergic signaling field.
Pyridoxal 5'-phosphate is an ATP-Receptor antagonist in freshly isolated rat cardiomyocytes
1999, Journal of Molecular and Cellular CardiologyAlthough extracellular ATP is considered to exert a positive inotropic action on the myocardium through purinoceptors, very little information is available regarding interventions which may modify the actions of ATP on the heart. We report here that pyridoxal 5′-phosphate (PLP), an active form of vitamin B6, shows antagonism towards ATP-induced positive inotropic effect in isolated perfused rat hearts, ATP-induced increase in [Ca2+] in freshly isolated adult cardiomyocytes and ATP-binding in cardiac sarcolemma; ED50for PLP in each of these cases varied from 10–15μm . PLP (5–50μm) was observed to antagonize the positive inotropic effect of ATP but did not modify the action of isoproterenol in the isolated perfused heart. Preincubation of cardiomyocytes with 1–50μm PLP prevented the ATP-induced increase in [Ca2+]iin a concentration-dependent manner but showed no effect on the KCl-induced increase in [Ca2+]i. Creatine phosphate and Na2HPO4as well as vitamin B6-related compounds, such as pyridoxine, pyridoxal, 4-deoxypyridoxine and isonicotinic acid hydrazide showed no effect on the ATP-induced increase in [Ca2+]iin cardiomyocytes. Furthermore, different concentrations of PLP (1–50μm) were shown to inhibit the specific ATPγS binding at both the high and low affinity sites in the cardiac sarcolemmal membrane; adrenoceptor and Ca2+-channel inhibitors did not affect the ATP-binding. It is concluded that PLP may antagonize the actions of ATP on the heart in a selective manner and both pyridoxal and phosphate moieties are essential for its action. Furthermore, it is suggested that PLP may serve as a valuable tool for monitoring the role of purinoceptors in cellular function.
Relaxant effect of 2-methyl-thio-adenosine diphosphate on rat thoracic aorta: Effect of clopidogrel
1999, European Journal of PharmacologyThe main aim of this study was to determine the functional effect of 2-methyl-thio-adenosine diphosphate (2MeS-ADP) on vascular purinoceptors, in comparison with that of a characterised agonist of the P2Y1 receptor, 2-methyl-thio-adenosine triphosphate (2MeS-ATP), and of the P2Y2 receptor, uridine triphosphate (UTP). On phenylephrine-precontracted rat aortic rings, mounted isometrically in organ baths, we found that 2MeS-ADP (10−9 to 10−6 M) induced concentration-dependent relaxation of rings with a functional endothelium. Mechanical removal of the endothelium abolished the relaxant effect of 2MeS-ADP. The 2MeS-ADP-induced relaxation of phenylephrine-precontracted rings was inhibited by Nω-nitro-l-arginine methyl ester (l-NAME) (100 μM) but not by indomethacin (100 μM) or aspirin (1 mM), indicating that the 2MeS-ADP-induced relaxation was nitric oxide (NO) synthase-mediated but not cyclooxygenase-dependent. Repeated stimulation with 2MeS-ADP resulted in desensitisation of the receptor. Under these conditions, the relaxant effect of 2MeS-ATP was abolished. On the contrary, UTP-induced relaxation was not affected, showing that 2MeS-ADP and 2MeS-ATP but not UTP shared the same receptor. Suramin (100 μM), a non-specific P2 inhibitor, abolished the effect of 2MeS-ADP, 2MeS-ATP and UTP. In contrast, pyridoxal-phosphate-6-azophenyl-2′-4′-disulphonic acid (PPADS) and adenosine-3′-phosphate-5′-phosphosulphate (A3P5PS) abolished only the vasodilator responses to 2MeS-ADP and 2MeS-ATP and did not affect the relaxant effect of UTP, showing that 2MeS-ADP acted through the P2Y1 receptor. Clopidogrel, a potent platelet ADP receptor antagonist, at a dose that strongly inhibited ADP-induced platelet aggregation ex vivo, did not modify the relaxant responses to 2MeS-ADP or 2MeS-ATP. In conclusion, these results showed that 2MeS-ADP induces endothelium-dependent, NO-mediated relaxation of rat aortic rings. This effect, resistant to clopidogrel treatment, occurred through activation of the P2Y1 receptor.
Nucleotide-evoked relaxation of human coronary artery
1998, European Journal of PharmacologyEndothelium-dependent dilation of coronary blood vessels in response to ATP and related nucleotides has been demonstrated in various animal species. The aim of the present study was to investigate a possible relaxant effect of ATP, the adenine nucleotides 2-methylthio ATP (MeSATP) and adenosine 5′-O-(2-thiodiphosphate) (ADPβS), and the pyrimidine nucleotide UTP in isolated human coronary artery. In endothelium-intact rings of human coronary artery precontracted with K+ (20–40 mM), the nucleotides caused relaxation. Average maximal percentage relaxations and average EC50 values (concentrations causing half-maximal relaxation) were 89% and 47.1 μM for ATP, 28% and 0.3 μM for MeSATP, 35% and 0.6 μM for ADPβS, and 49% and 1.6 μM for UTP. For each of the four agonists, the potency to elicit relaxation varied greatly between individual rings, so that equi-relaxing concentrations spanned several orders of magnitude. Moreover, the sensitivities to ATP and UTP, when tested in the same ring, were not correlated. Mechanical removal of the endothelium as well as NG-nitro-l-arginine methyl ester (l-NAME; 30 μM), an inhibitor of nitric oxide synthase, abolished the relaxation caused by MeSATP, ADPβS and UTP and greatly attenuated the response to lower concentrations of ATP (3.2–320 μM), but high concentrations of ATP (320 and 1000 μM) caused relaxation also in endothelium-denuded preparations and in the presence of l-NAME. High concentrations of ADPβS (32 and 100 μM) and UTP (320 and 1000 μM) caused contraction of endothelium-denuded preparations. Thus, extracellular nucleotides cause endothelium-dependent, primarily nitric oxide-mediated relaxation of human coronary artery. ATP in addition causes endothelium-independent relaxation. The receptors activated by the nucleotides appear to be unevenly distributed on the coronary endothelium.
Evidence that P2X purinoceptors mediate the excitatory effects of αβmethylene-ADP in rat locus coeruleus neurones
1998, NeuropharmacologyExtracellular and whole-cell patch clamp recordings were used to study the excitatory responses elicited by purine nucleotides in pontine slices of the rat brain containing the locus coeruleus (LC). The P2 purinoceptor agonists, αβ-methyleneadenosine 5′-triphosphate (αβmeATP) and adenosine 5′-O-(2-thiodiphosphate) (ADPβS), and a novel purinoceptor agonist, αβ-methyleneadenosine 5′-diphosphate (αβmeADP), elicited concentration-dependent increases in the spontaneous firing rate over the concentration range (1–300 μM). On vagus nerve or dorsal root preparations αβmeADP (100 μM) had no agonist activity. In the presence of both αβmeATP (300 μM), ADPβS (300 μM) elicited a further and significant increase in the firing rate of the LC neurones, whilst neither αβmeATP nor αβmeADP (of 300 μM) elicited a further response. The P2 purinoceptor antagonists, suramin (100 μM) and pyridoxalphosphate-6-azophenyl-2′,4′-disulphonic acid (PPADS; 30 μM), markedly attenuated responses to all three agonists. Whole-cell recording of membrane current showed that, at −60 mV, αβmeATP and αβmeADP (both 100 μM) elicited inward currents of a similar magnitude, whilst the inward currents elicited by a lower concentration of ADPβS (30 μM) were larger and faded in the presence of this agonist. In the presence of tetrodotoxin and a combination of other neurotransmission blockers, both αβmeATP and αβmeADP still produced inward currents. Based on the known selectivity of the agonists used in this study, there appear to be two distinct P2 purinoceptor types present on neurones in the LC, which correspond to the P2X and P2Y types. The responses elicited by αβmeADP appear to be mediated through a putative P2X purinoceptor, although further work is required to determine which P2X receptor subtype(s) are involved.
Functional evidence for multiple purinoceptor subtypes in the rat medial vestibular nucleus
1997, NeuroscienceExtracellular recording techniques were used in brain slices to characterize excitatory responses produced by purine nucleotides in the rat medial vestibular nucleus, an area where functional purinoceptors have not previously been described. In the continued presence of the adenosine antagonist 8-cyclopentyl-1,3-dipropylxanthine, which alone caused a small increase in the spontaneous firing rate, the P2 purinoceptor agonists α,β-methyleneadenosine 5′-triphosphate and adenosine 5′-O-(2-thiodiphosphate) caused concentration-dependent increases in spontaneous firing rate, with ec50 values of 1.7 and 41.8 μM, respectively. Only approximately 35% of all neurons studied displayed excitatory responses to these agents. Responses waned in the continued presence of high concentrations of the latter, but not the former agonist. Furthermore, in the continued presence of a maximal concentration of α,β-methyleneadenosine 5′-triphosphate, adenosine 5′-O-(2-thiodiphosphate) produced further increases in the firing rate of these neurons. The P2 antagonist, suramin, ablated responses to α,β-methyleneadenosine 5′-triphosphate, but did not affect responses to adenosine 5′-O-(2-thiodiphosphate), whereas pyridoxal-phosphate-6-azophenyl-2′,4′-disulphonic acid antagonized responses to both agonists. The nucleotide analogue α,β-methyleneadenosine 5′-diphosphate, which displays affinity for putative P2X receptors in brain, also produced concentration-dependent increases in firing frequency, which were also markedly antagonized in the presence of suramin, this agonist being only slightly less potent than α,β-methyleneadenosine 5′-triphosphate.
In conclusion, a subpopulation of rat medial vestibular neuronal responses mediated by both P2X and P2Y purinoceptors can be distinguished, in addition to the presence of P1 receptors for adenosine. Comparison of these P2 purinoceptors with the properties of recombinantly expressed P2X and P2Y receptors suggests that these endogenous P2 purinoceptors differ in several important aspects from heterologously expressed recombinant receptors identified from cloning studies.