Permeability and single‐channel properties of mesenteric, basilar, and septal (coronary) artery smooth‐muscle P2X receptors

Lewis, Carolyn J.; Davies, Noel W.; Evans, Richard J.

doi:10.1002/ddr.1111

Cited by 2 publications

(4 citation statements)

References 16 publications

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“…Although the extrapolation of such data to provide an estimate of pore size needs to be interpreted with caution (as discussed in Ref. 17), it is interesting to note that the estimated minimum pore diameter for schP2X (ϳ0.9 nM) correlates well with that estimated for human P2X 1 and P2X 2 (ϳ0.8 nM) (17,27), suggesting that the ion permeation pathway and selectivity filter are also conserved between these evolutionary remote channels.…”

Section: Discussionmentioning

confidence: 95%

“…Calcium Permeability-The relative permeability to calcium was determined from the reversal potential of schP2X currents in 112 mM extracellular calcium solution as described previously (17,27). In 112 mM external calcium, currents in response to 100 M ATP were 90 Ϯ 2.7% (p Ͻ 0.01) smaller than the equivalent currents in 154 mM external sodium solution.…”

Section: Potentiation Of Schp2xmentioning

confidence: 99%

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Functional Characterization of a P2X Receptor from Schistosoma mansoni

Agboh

Webb

Evans

et al. 2004

Journal of Biological Chemistry

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The cloning and characterization of a P2X receptor (schP2X) from the parasitic blood fluke Schistosoma mansoni provides the first example of a non-vertebrate ATP-gated ion channel. A number of functionally important amino acid residues conserved throughout vertebrate P2X receptors, including 10 extracellular cysteines, aromatic and positively charged residues involved in ATP recognition, and a consensus protein kinase C site in the amino-terminal tail, are also present in schP2X. Overall, the amino acid sequence identity of schP2X with human P2X 1-7 receptors ranges from 25.8 to 36.6%. ATP evoked concentration-dependent currents at schP2X channels expressed in Xenopus oocytes with an EC 50 of 22.1 M. 2,3-O-(4-Benzoylbenzoyl)adenosine 5-triphosphate (Bz-ATP) was a partial agonist (maximum response 75.4 ؎ 4.4% that of ATP) with a higher potency (EC 50 of 3.6 M) than ATP. Suramin and pyridoxal-phosphate-6-azophenyl-2,4-disulfonic acid blocked schP2X responses to 100 M ATP with IC 50 values of 9.6 and 0.5 M, respectively. Ivermectin (10 M) potentiated currents to both ATP and Bz-ATP by ϳ60% with a minimal effect on potency (EC 50 of 18.2 and 1.6 M, respectively). The relative permeability of schP2X expressed in HEK293 cells to various cations was determined under bi-ionic conditions. schP2X has a relatively high calcium permeability (P Ca /P Na ‫؍‬ 3.80 ؎ 0.29) and an estimated minimum pore diameter similar to that of vertebrate P2X receptors. SchP2X provides a useful comparative model for the better understanding of human P2X receptor function and may also provide an alternative drug target for treatment of schistosomiasis.P2X receptors comprise a family of cation-selective ion channels gated by extracellular ATP. Mammalian species possess seven distinct P2X channel subtypes (P2X 1-7 ), each encoded by a separate gene. These subunits assemble as functional homotrimeric or heterotrimeric channels and play an important role in a wide array of physiological processes including neurotransmission, smooth muscle contraction, immune cell function, and platelet aggregation (for a recent review see Ref. 1).This remarkably diverse range of physiological roles for P2X receptors has contributed to the notion that ATP is a "primitive" extracellular signaling molecule (2, 3). Functional evidence suggests that ATP-gated ion channels exist in some lower organisms including Tetrahymena thermophilia (4), leech (5), and Amoeba proteus (6), supporting the view that the development of P2X receptors for ATP occurred relatively early in the evolution of eukaryotic organisms. However, to date, definitive molecular identification of P2X channels is restricted to vertebrate species including fish (7), amphibians (8, 9), birds (10), and mammals (1).With the recent expansion in the range of species for which genomic and EST 1 sequence databases are available, it is now possible to use a bioinformatics approach to screen a wide range of lower organisms for P2X receptor-like proteins. Using such a strategy, we have identified a P2X channel from...

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Section: Discussionmentioning

confidence: 95%

Section: Potentiation Of Schp2xmentioning

confidence: 99%

Functional Characterization of a P2X Receptor from Schistosoma mansoni

Agboh

Webb

Evans

et al. 2004

Journal of Biological Chemistry

Self Cite

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“…In arteries P2X 1 receptors do not appear to be randomly distributed throughout the plasma membrane as P2X 1 receptor immunoreactivity appears in clusters (23). This clustering of receptors is supported by electrophysioliogical studies on dissociated artery muscle excised membrane patches; some patches had multiple P2X receptor channels whilst channel activity was absent in others (24). Recent studies also indicate that the P2X 1 receptors can be regulated by phosphorylation of interacting proteins (25) suggesting that the P2X 1 receptor exists in an organised signalling domain.…”

Section: Introductionmentioning

confidence: 83%

“…The association of P2X 1 receptors in lipid rafts may not only be important in maintaining the responsiveness of the receptor but may also be a mechanism to achieve clustering of the receptor. Immunohistochemical and single channel recording studies have indicated that the P2X 1 receptor is not randomly distributed in the membrane but forms clusters (23,24) and that in smooth muscle preparations these clusters are often seen close to sympathetic nerve varicosities; the site of transmitter release. Thus lipid rafts may be a way of concentrating the P2X 1 receptor at signalling hot-spots.…”

Section: Discussionmentioning

confidence: 99%

Disruption of Lipid Rafts Inhibits P2X1 Receptor-mediated Currents and Arterial Vasoconstriction

Vial

Evans

2005

Journal of Biological Chemistry

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P2X 1 receptors for ATP are ligand-gated cation channels expressed on a range of smooth muscle preparations and blood platelets. The receptors appear to be clustered close to sympathetic nerve varicosities and mediate the underlying membrane potential changes and constriction following nerve stimulation in a range of arteries and resistance arterioles. In this study we have used discontinuous sucrose density gradients, Western blot analysis, and cholesterol measurements to show that recombinant and smooth muscle (rat tail artery, vas deferens, and bladder) P2X 1 receptors are present in cholesterol-rich lipid rafts and co-localize with the lipid raft markers flotillin-1 and -2. Lipid rafts are specialized lipid membrane microdomains involved in signaling and trafficking. To determine whether lipid raft association was essential for P2X 1 receptor channel function we used the cholesterol-depleting agent methyl-␤-cyclodextrin (10 mM for 1 h). This led to a redistribution of the P2X 1 receptor throughout the sucrose gradient and reduced P2X 1 receptor-mediated (␣,␤-methylene ATP, 10 M) currents in HEK293 cells by >90% and contractions of the rat tail artery by ϳ50%. However contractions evoked by potassium chloride (60 mM) were unaffected by methyl-␤-cyclodextrin and the inactive analogue ␣-cyclodextrin had no effect on P2X 1 receptor-mediated currents or contractions. P2X 1 receptors are subject to ongoing regulation by receptors and kinases, and the present results suggest that lipid rafts are an essential component in the maintenance of these localized signaling domains and play an important role in P2X 1 receptor-mediated control of arteries.ATP released from nerves following tissue damage or shear stress acts at P2 receptors to regulate cardiovascular function (1). P2 receptors are divided into ligand-gated P2X receptor channels and G-protein-coupled P2Y receptors. P2X receptormediated vasoconstriction has been described in a range of arteries in the periphery (1) and in the brain (2). Sympathetic nerves co-store and co-release ATP and noradrenaline, and the relative contribution of purinergic and noradrenergic mechanisms to vasoconstriction is dependent on the size of the vessel and the parameters of stimulation (3, 4). The P2X receptormediated component predominates in small diameter arteries (4, 5) and in submucosal resistance arterioles P2X receptor activation is solely responsible for sympathetic neurogenic vasoconstriction with noradrenaline acting through presynaptic mechanisms to regulate transmitter release (6). In addition P2X receptor channels in smooth muscle are permeant to calcium (ϳ10% of current flowing through the channel under physiological conditions, Refs. 7 and 8), and a substantial component of the calcium required for contraction enters by this route (4, 9). P2X receptors therefore provide a mechanism for sympathetic nerve-mediated regulation of vascular tone that is resistant to ␣-adrenoreceptor and calcium channel antagonists.Seven P2X receptor subunits have been identified (P2X 1-7 ),...

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Permeability and single‐channel properties of mesenteric, basilar, and septal (coronary) artery smooth‐muscle P2X receptors

Cited by 2 publications

References 16 publications

Functional Characterization of a P2X Receptor from Schistosoma mansoni

Functional Characterization of a P2X Receptor from Schistosoma mansoni

Disruption of Lipid Rafts Inhibits P2X1 Receptor-mediated Currents and Arterial Vasoconstriction

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