(1/442) Expression of both P1 and P2 purine receptor genes by human articular chondrocytes and profile of ligand-mediated prostaglandin E2 release.
OBJECTIVE: To assess the expression and function of purine receptors in articular chondrocytes. METHODS: Reverse transcriptase-polymerase chain reaction (RT-PCR) was used to screen human chondrocyte RNA for expression of P1 and P2 purine receptor subtypes. Purine-stimulated prostaglandin E2 (PGE2) release from chondrocytes, untreated or treated with recombinant human interleukin-1alpha (rHuIL-1alpha), was assessed by radioimmunoassay. RESULTS: RT-PCR demonstrated that human articular chondrocytes transcribe messenger RNA for the P1 receptor subtypes A2a and A2b and the P2 receptor subtype P2Y2, but not for the P1 receptor subtypes A1 and A3. The P1 receptor agonists adenosine and 5'-N-ethylcarboxamidoadenosine did not change PGE2 release from chondrocytes. The P2Y2 agonists ATP and UTP stimulated a small release of PGE2 that was potentiated after pretreatment with rHuIL-1alpha. PGE2 release in response to ATP and UTP cotreatment was not additive, but release in response to coaddition of ATP and bradykinin (BK) or UTP and BK was additive, consistent with ATP and UTP competition for the same receptor site. The potentiation of PGE2 release in response to ATP and UTP after rHuIL-1alpha pretreatment was mimicked by phorbol myristate acetate. CONCLUSION: Human chondrocytes express both P1 and P2 purine receptor subtypes. The function of the P1 receptor subtype is not yet known, but stimulation of the P2Y2 receptor increases IL-1-mediated PGE2 release. (+info)
(2/442) Desensitization of P2Y2 receptor-activated transepithelial anion secretion.
Desensitization of P2Y2 receptor-activated anion secretion may limit the usefulness of extracellular nucleotides in secretagogue therapy of epithelial diseases, e.g., cystic fibrosis (CF). To investigate the desensitization process for endogenous P2Y2 receptors, freshly excised or cultured murine gallbladder epithelia (MGEP) were mounted in Ussing chambers to measure short-circuit current (Isc), an index of electrogenic anion secretion. Luminal treatment with nucleotide receptor agonists increased the Isc with a potency profile of ATP = UTP > 2-methylthioATP >> alpha,beta-methylene-ATP. RT-PCR revealed the expression of P2Y2 receptor mRNA in the MGEP cells. The desensitization of anion secretion required a 10-min preincubation with the P2Y2 receptor agonist UTP and increased in a concentration-dependent manner (IC50 approximately 10(-6) M). Approximately 40% of the anion secretory response was unaffected by maximal desensitizing concentrations of UTP. Recovery from UTP-induced desensitization was rapid (<10 min) at preincubation concentrations less than the EC50 (1.9 x 10(-6) M) but required progressively longer time periods at greater concentrations. UTP-induced total inositol phosphate production and intracellular Ca2+ mobilization desensitized with a concentration dependence similar to that of anion secretion. In contrast, maximal anion secretion induced by Ca2+ ionophore ionomycin was unaffected by preincubation with a desensitizing concentration of UTP. It was concluded that 1) desensitization of transepithelial anion secretion stimulated by the P2Y2 receptor agonist UTP is time and concentration dependent; 2) recovery from desensitization is prolonged (>90 min) at UTP concentrations >10(-5) M; and 3) UTP-induced desensitization occurs before the operation of the anion secretory mechanism. (+info)
(3/442) Functional and biochemical evidence for heteromeric ATP-gated channels composed of P2X1 and P2X5 subunits.
The mammalian P2X receptor gene family encodes two-transmembrane domain nonselective cation channels gated by extracellular ATP. Anatomical localization data obtained by in situ hybridization and immunocytochemistry have shown that neuronal P2X subunits are expressed in specific but overlapping distribution patterns. Therefore, the native ionotropic ATP receptors diversity most likely arises from interactions between different P2X subunits that generate hetero-multimers phenotypically distinct from homomeric channels. Rat P2X1 and P2X5 mRNAs are localized within common subsets of peripheral and central sensory neurons as well as spinal motoneurons. The present study demonstrates a functional association between P2X1 and P2X5 subunits giving rise to hybrid ATP-gated channels endowed with the pharmacology of P2X1 and the kinetics of P2X5. When expressed in Xenopus oocytes, hetero-oligomeric P2X1+5 ATP receptors were characterized by slowly desensitizing currents highly sensitive to the agonist alpha,beta-methylene ATP (EC50 = 1.1 microM) and to the antagonist trinitrophenyl ATP (IC50 = 64 nM), observed with neither P2X1 nor P2X5 alone. Direct physical evidence for P2X1+5 co-assembly was provided by reciprocal subunit-specific co-purifications between epitope-tagged P2X1 and P2X5 subunits transfected in HEK-293A cells. (+info)
(4/442) ATP is a mediator of the fast inhibitory junction potential in human jejunal circular smooth muscle.
The neurotransmitter(s) that generates the fast component of the inhibitory junction potential (IJP-F) in human jejunal circular smooth muscle is not known. The aim of this study was to determine the role of ATP and purinergic receptors in the generation of the IJP-F in human jejunal circular smooth muscle strips. The P2-receptor antagonist suramin (100 microM) reduced the IJP-F by 28%. Apamin (1 microM) reduced the IJP-F by 25%. Desensitization of muscle strips with the putative P2x-receptor agonist alpha, beta-methylene ATP (alpha,beta-MeATP, 100 microM) decreased the IJP-F by 44%, and desensitization with the putative P2y-receptor agonist adenosine 5'-O-2-thiodiphosphate (ADPbetaS) completely abolished the IJP-F. Desensitization with the putative P2y-receptor agonist 2-methylthioATP had no effect on the IJP-F. Exogenous ATP evoked a hyperpolarization with a time course that matched the IJP-F. The ATP-evoked hyperpolarization was reduced by apamin and suramin, reduced by desensitization with alpha,beta-MeATP (69% decrease), and abolished by desensitization with ADPbetaS. These data suggest that the IJP-F in human jejunal circular smooth muscle is mediated in part by ATP through an ADPbetaS-sensitive P2 receptor. (+info)
(5/442) Multiple functional P2X and P2Y receptors in the luminal and basolateral membranes of pancreatic duct cells.
Purinergic receptors in the basolateral and luminal membranes of the pancreatic duct can act by a feedback mechanism to coordinate transport activity in the two membranes during ductal secretion. The goal of the present work was to identify and localize the functional P2 receptors (P2R) in the rat pancreatic duct. The lack of selective agonists and/or antagonists for any of the cloned P2R dictated the use of molecular and functional approaches to the characterization of ductal P2R. For the molecular studies, RNA was prepared from microdissected pancreatic intralobular ducts and was shown to be free of mRNA for amylase and endothelial nitric oxide synthase (markers for acinar and endothelial cells, respectively). A new procedure is described to obtain an enriched preparation of single duct cells suitable for electrophysiological studies. Localization of P2R was achieved by testing the effect of various P2R agonists on intracellular Ca(2+) concentration ([Ca(2+)](i)) of microperfused intralobular ducts. RT-PCR analysis suggested the expression of six subtypes of P2R in the pancreatic duct: three P2YR and three P2XR. Activation of Cl(-) current by various nucleotides and coupling of the receptors activated by these nucleotides to G proteins confirmed the expression of multiple P2R in duct cells. Measurement of [Ca(2+)](i) in microperfused intralobular ducts suggested the expression of P2X(1)R, P2X(4)R, probably P2X(7)R, and as yet unidentified P2YR, possibly P2Y(1)R, in the basolateral membrane. Expression of P2Y(2)R, P2Y(4)R, and P2X(7)R was found in the luminal membrane. The unprecedented expression of such a variety of P2R in one cell type, many capable of activating Cl(-) channels, suggests that these receptors may have an important role in pancreatic duct cell function. (+info)
(6/442) Regulation by P2 agonists of the intracellular calcium concentration in epithelial cells freshly isolated from rat trachea.
Epithelial cells were isolated from rat trachea by incubation of the organ in a calcium-free medium. The intracellular concentration of calcium ([Ca(2+)](i)) was measured with the calcium-sensitive fluorescent dye fura2. In resting conditions, the cells maintained a low [Ca(2+)](i) in spite of the presence of millimolar concentration of calcium in the incubation medium. These cells had retained intracellular stores of calcium which were emptied after exposure of the cells to thapsigargin, an inhibitor of intracellular calcium ATPases. Substance P (125 nM) transiently increased 2.5-fold the [Ca(2+)](i). ATP (1 mM) doubled the [Ca(2+)](i) after a few seconds and further induced a sustained increase of the [Ca(2+)](i). Coomassie blue fully blocked the response to ATP and extracellular magnesium only inhibited the delayed response to ATP. Among purinergic analogs, only benzoyl-ATP (Bz-ATP), an agonist on P2X ionotropic purinergic receptors, reproduced the response to ATP. UTP and 2-methylthioATP (two agonists on P2Y metabotropic purinergic receptors) transiently increased the [Ca(2+)](i). Thapsigargin, ATP and Bz-ATP increased the uptake of extracellular calcium. RT-PCR analysis revealed that two metabotropic receptors (P2Y(1) and P2Y(2)) and two ionotropic receptors (P2X(4) and P2X(7)) were expressed by the cells present in the suspension. It is concluded that purinergic agonists can modulate the response of rat tracheal epithelial cells by several mechanisms. The activation of metabotropic receptors should mobilize intracellular IP(3)-sensitive calcium pools. The activation of the ionotropic receptors should not only open a non-specific cation channel leading to the entry of calcium but should also induce the formation of pores in cells expressing the P2X(7) receptors, which could be deleterious to these cells. (+info)
(7/442) Nucleotide stimulation of Cl(-) secretion in the pigmented rabbit conjunctiva.
We evaluated the role of extracellular UTP and other nucleotides in the regulation of active ion transport across the pigmented rabbit conjunctiva. When added to the mucosal side of the conjunctiva, UTP (0.01-1000 microM), increased the short-circuit current by up to 14. 6 +/- 2.1 microA/cm(2). The half-maximal concentration was 11.4 +/- 2.3 microM. The serosal absence of Cl(-), serosal presence of 10 microM bumetanide, and mucosal presence of 0.3 mM N-phenylanthranilic acid significantly reduced the change in the short-circuit current (DeltaIsc) induced by 10 microM UTP by 78, 77, and 42%, respectively. Mucosal 10 microM UTP significantly increased (36)Cl flux in the serosal-to-mucosal direction by 0.17 microEq/cm(2)/h, while not affecting mucosal-to-serosal (36)Cl flux. By contrast, (22)Na transport in either direction was unaffected. The rank order of DeltaIsc elicited by adenosine and nucleotides was consistent with the predominant involvement of P2Y purinergic receptors in the UTP effect on conjunctival ion transport. Moreover, the DeltaIsc elicited by UTP was inhibited by 0.05 and 1 mM suramin (a P2-purinergic receptor antagonist), resulting in a rightward shift of the half-maximal concentration to 106.7 +/- 1.3 microM. In conclusion, the primary effect of UTP on ion transport in the pigmented rabbit conjunctiva is stimulation of Cl(-) secretion, possibly at the P2Y(2) and/or the P2Y(4) receptor on the mucosal side of the tissue. Because of the coupling of fluid flow with Cl(-) secretion, UTP or its analogs may be considered for stimulating transconjunctival fluid flow in the dry-eye state. (+info)
(8/442) Properties of the novel ATP-gated ionotropic receptor composed of the P2X(1) and P2X(5) isoforms.
We recently reported that a novel hetero-oligomeric P2X receptor is formed from the P2X(1) and P2X(5) isoforms when coexpressed in human embryonic kidney 293 cells (). A more complete description of the pharmacology of this novel receptor is presented here. A brief application of ATP to a voltage-clamped cell transiently expressing P2X(1/5) receptors resulted in a biphasic current that rapidly reached a peak and then decayed to a sustained plateau. Washout of ATP was accompanied by generation and fade of a pronounced tail of inward current. EC(50) values were determined from concentration-response curves for a range of agonists. The rank order of agonist potency was ATP >/= 2 methylthio ATP > adenosine 5'-O-(3-thiotriphosphate) > alpha,beta-methylene ATP > ADP > CTP. alpha,beta-methylene ADP, UTP, GTP, and AMP were ineffective. Only ATP and 2 methylthio ATP were full agonists. IC(50) values were determined from concentration-response curves for three commonly used purinergic antagonists. Suramin and pyridoxal phosphate-6-azophenyl-2', 4'-disulfonic acid were equipotent at P2X(1) and P2X(1/5) receptors; however, the P2X(1/5) receptor was much less sensitive to TNP-ATP than was the P2X(1) receptor. The amplitude of peak ATP-gated current was relatively insensitive to changes in [Ca(2+)](O) (1-30 mM). Finally, plateau currents were potentiated by low concentrations of pyridoxal phosphate-6-azophenyl-2', 4'-disulfonic acid and by raising [Ca(2+)](O). These results provide additional information on the pharmacological profile of the recombinant P2X(1/5) receptor channel and provide a basis to further evaluate ATP-induced currents in native tissues. (+info)