Differential effects of uridine adenosine tetraphosphate on purinoceptors in the rat isolated perfused kidney.
ABSTRACT Purinergic signalling plays an important role in vascular tone regulation in humans. We have identified uridine adenosine tetraphosphate (Up(4)A) as a novel and highly potent endothelial-derived contracting factor. Up(4)A induces strong vasoconstrictive effects in the renal vascular system mainly by P2X(1) receptor activation. However, other purinoceptors are also involved and were analysed here.
The rat isolated perfused kidney was used to characterize vasoactive actions of Up(4)A.
After desensitization of the P2X(1) receptor by α,β-methylene ATP (α,β-meATP), Up(4)A showed dose-dependent P2Y(2)-mediated vasoconstriction. Continuous perfusion with Up(4)A evoked a biphasic vasoconstrictor effect: there was a strong and rapidly desensitizing vasoconstriction, inhibited by P2X(1) receptor desensitization. In addition, there is a long-lasting P2Y(2)-mediated vasoconstriction. This vasoconstriction could be blocked by suramin, but not by PPADS or reactive blue 2. In preparations of the rat isolated perfused kidney model with an elevated vascular tone, bolus application of Up(4)A showed a dose-dependent vasoconstriction that was followed by a dose-dependent vasodilation. The vasoconstriction was in part sensitive to P2X(1) receptor desensitization by α,β-meATP, and the remaining P2Y(2)-mediated vasoconstriction was only inhibited by suramin. The Up(4)A-induced vasodilation depended on activation of nitric oxide synthases, and was mediated by P2Y(1) and P2Y(2) receptor activation.
Up(4)A activated P2X(1) and P2Y(2) receptors to act as a vasoconstrictor, whereas endothelium-dependent vasodilation was induced by P2Y(1/2) receptor activation. Up(4)A might be of relevance in the physiology and pathophysiology of vascular tone regulation.
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ABSTRACT: The newly recognized human endogenous vasoconstrictive dinucleotides, diadenosine pentaphosphate (AP5A) and diadenosine hexaphosphate (AP6A), were tested for growth stimulatory effects in rat mesangial cells (MC). Both AP5A and AP6A stimulated growth in micromolar concentrations. The growth stimulatory effect exceeded that of ATP, alpha,beta-methylene ATP, adenosine 5'-O-(3-thio)triphosphate and UTP. Both diadenosine phosphates potentiated the growth response to platelet-derived growth factor, but not to insulin-like growth factor-1. To further elucidate the site of action in the cell cycle, RNA and protein synthesis were assessed. AP5 and AP6A stimulated protein synthesis, but not RNA formation. Furthermore, both agents increased cytosolic free Ca2+ concentration. It is concluded that AP5A and AP6A may play a regulatory role in MC growth as progression factors and possibly modify MC proliferation in glomerular disease.Journal of Clinical Investigation 07/1995; 95(6):2862-7. · 15.39 Impact Factor
Article: The critical role of adenosine and guanosine in the affinity of dinucleoside polyphosphates to P(2X)-receptors in the isolated perfused rat kidney.[show abstract] [hide abstract]
ABSTRACT: 1. The activation of P(2x)-receptors in the rat renal vasculature by dinucleoside polyphosphates with variable phosphate group chain length (Xp(n)X; X=Adenin (A) /Guanin (G), n=4 - 6) was studied by measuring their effects on perfusion pressure of the isolated perfused rat kidney at constant flow in an open circuit. 2. Like Ap(4)A, Ap(5)A and Ap(6)A the dinucleoside polyphosphates Ap(4)G, Ap(5)G and Ap(6)G exerted a vasoconstriction which could be blocked by suramin and pyridoxal-phosphate-6-azophenyl-2; 4-disulphonic acid (PPADS). 3. Gp(4)G, Gp(5)G and Gp(6)G showed only very weak vasoconstriction at high doses. 4. Ap(6)A and alpha, beta-meATP could not be blocked by the selective P(2x1)-receptor antagonisten NF023 (30 microM), whereas Ap(4)A, Ap(4)G, Ap(5)A, Ap(5)G and Ap(6)G were partially blocked by NF023. 5. Inhibition of endothelial NO-synthase by N(omega)-nitro-L-arginine methyl ester (L-NAME) did not affect vasoconstrictions induced by dinucleosidepolyphosphates. 6. P(2x)-receptor can only be activated if at least one adenosine moiety is present in the molecule. 7. Ap(n)G show a weaker vasoconstrictive action than corresponding Ap(n)A, concluding that two adenosine moieties enhance the P(2x)-receptor binding and activation. 8. Xp(n)X containing five phosphate groups show the most pronounced vasoconstrictive effect whereas four phosphate groups show the less effect, therefore the number of phosphate groups critically changes receptor affinity. 9. Additional experiments using permanent perfusion with alpha, beta-methylene ATP (alpha,beta-meATP) and the selective P(2x1)-receptor antagonist NF023 showed that the newly discovered human dinucleoside polyphosphates activated the vascular P(2x1)-receptor and an recently identified new P(2x)-receptor subtype. 10. The differential effects of dinucleoside polyphosphates allow a fine tuning of local perfusion via composition of Xp(n)Xs.British Journal of Pharmacology 02/2001; 132(2):467-74. · 4.41 Impact Factor
Article: Paracrine regulation of the epithelial Na+ channel in the mammalian collecting duct by purinergic P2Y2 receptor tone.[show abstract] [hide abstract]
ABSTRACT: Growing evidence implicates a key role for extracellular nucleotides in cellular regulation, including of ion channels and renal function, but the mechanisms for such actions are inadequately defined. We investigated purinergic regulation of the epithelial Na+ channel (ENaC) in mammalian collecting duct. We find that ATP decreases ENaC activity in both mouse and rat collecting duct principal cells. ATP and other nucleotides, including UTP, decrease ENaC activity via apical P2Y2 receptors. ENaC in collecting ducts isolated from mice lacking this receptor have blunted responses to ATP. P2Y2 couples to ENaC via PLC; direct activation of PLC mimics ATP action. Tonic regulation of ENaC in the collecting duct occurs via locally released ATP; scavenging endogenous ATP and inhibiting P2 receptors, in the absence of other stimuli, rapidly increases ENaC activity. Moreover, ENaC has greater resting activity in collecting ducts from P2Y2-/- mice. Loss of collecting duct P2Y2 receptors in the knock-out mouse is the primary defect leading to increased ENaC activity based on the ability of direct PLC stimulation to decrease ENaC activity in collecting ducts from P2Y2-/- mice in a manner similar to ATP in collecting ducts from wild-type mice. These findings demonstrate that locally released ATP acts in an autocrine/paracrine manner to tonically regulate ENaC in mammalian collecting duct. Loss of this intrinsic regulation leads to ENaC hyperactivity and contributes to hypertension that occurs in P2Y2 receptor-/- mice. P2Y2 receptor activation by nucleotides thus provides physiologically important regulation of ENaC and electrolyte handling in mammalian kidney.Journal of Biological Chemistry 12/2008; 283(52):36599-607. · 4.77 Impact Factor