Suramin and reactive blue 2 are antagonists for a newly identified purinoceptor on rat megakaryocyte

Purinergic inhibitory regulation of esophageal smooth muscle is mediated by P2Y receptors and ATP-dependent potassium channels in rats

Purines such as ATP are regulatory transmitters in motility of the gastrointestinal tract. The aims of this study were to propose functional roles of purinergic regulation of esophageal motility. An isolated segment of the rat esophagus was placed in an organ bath, and mechanical responses were recorded using a force transducer. Exogenous application of ATP (10-100 μM) evoked relaxation of the esophageal smooth muscle in a longitudinal direction under the condition of carbachol (1 μM) -induced precontraction. Pretreatment with a non-selective P2 receptor antagonist, suramin (500 μM), and a P2Y receptor antagonist, cibacron blue F3GA (200 μM), inhibited the ATP (100 μM) -induced relaxation, but a P2X receptor antagonist, pyridoxal phosphate-6-azophenyl-2,4-disulfonic acid (50 μM), did not affect it. A blocker of ATP-dependent potassium channels (KATP channels), glibenclamide (200 μM), inhibited the ATP-induced relaxation and application of an opener of KATP channels, nicorandil (50 μM), produced relaxation. The findings suggest that ATP is involved in inhibitory regulation of the longitudinal smooth muscle in the muscularis mucosae of the rat esophagus via activation of P2Y receptors and then opening of KATP channels.

ATP-Induced Contractile Response of Esophageal Smooth Muscle in Mice

The tunica muscularis of mammalian esophagi is composed of striated muscle and smooth muscle. Contraction of the esophageal striated muscle portion is mainly controlled by cholinergic neurons. On the other hand, smooth muscle contraction and relaxation are controlled not only by cholinergic components but also by non-cholinergic components in the esophagus. Adenosine triphosphate (ATP) is known to regulate smooth muscle contraction and relaxation in the gastrointestinal tract via purinergic receptors. However, the precise mechanism of purinergic regulation in the esophagus is still unclear. Therefore, the aim of the present study was to clarify the effects of ATP on the mechanical responses of the esophageal muscle in mice. An isolated segment of the mouse esophagus was placed in a Magnus's tube and longitudinal mechanical responses were recorded. Exogenous application of ATP induced contractile responses in the esophageal preparations. Tetrodotoxin, a blocker of voltage-dependent sodium channels in neurons and striated muscle, did not affect the ATP-induced contraction. The ATP-evoked contraction was blocked by pretreatment with suramin, a purinergic receptor antagonist. RT-PCR revealed the expression of mRNA of purinergic receptor genes in the mouse esophageal tissue. The findings suggest that purinergic signaling might regulate the motor activity of mouse esophageal smooth muscle.

Brilliant Blue Dyes in Daily Food: How Could Purinergic System Be Affected?

Dyes were first obtained from the extraction of plant sources in the Neolithic period to produce dyed clothes. At the beginning of the 19th century, synthetic dyes were produced to color clothes on a large scale. Other applications for synthetic dyes include the pharmaceutical and food industries, which are important interference factors in our lives and health. Herein, we analyzed the possible implications of some dyes that are already described as antagonists of purinergic receptors, including special Brilliant Blue G and its derivative FD&C Blue No. 1. Purinergic receptor family is widely expressed in the body and is critical to relate to much cellular homeostasis maintenance as well as inflammation and cell death. In this review, we discuss previous studies and show purinergic signaling as an important issue to be aware of in food additives development and their correlations with the physiological functions.

Blood cells: an historical account of the roles of purinergic signalling

The involvement of purinergic signalling in the physiology of erythrocytes, platelets and leukocytes was recognised early. The release of ATP and the expression of purinoceptors and ectonucleotidases on erythrocytes in health and disease are reviewed. The release of ATP and ADP from platelets and the expression and roles of P1, P2Y(1), P2Y(12) and P2X1 receptors on platelets are described. P2Y(1) and P2X(1) receptors mediate changes in platelet shape, while P2Y(12) receptors mediate platelet aggregation. The changes in the role of purinergic signalling in a variety of disease conditions are considered. The successful use of P2Y(12) receptor antagonists, such as clopidogrel and ticagrelor, for the treatment of thrombosis, myocardial infarction and stroke is discussed.

Small molecule inhibitors of arginyltransferase regulate arginylation-dependent protein degradation, cell motility, and angiogenesis

Posttranslational arginylation mediated by arginyltransferase (ATE1) is an emerging major regulator of embryogenesis and cell physiology. Impairments of ATE1 are implicated in congenital heart defects, obesity, cancer, and neurodegeneration making this enzyme an important therapeutic target, whose potential has been virtually unexplored. Here we report the development of a biochemical assay for identification of small molecule inhibitors of ATE1 and application of this assay to screen a library of 3280 compounds. Our screen identified two compounds which specifically affect ATE1-regulated processes in vivo, including tannic acid, which has been previously shown to inhibit protein degradation and angiogenesis and to act as a therapeutic agent in heart disease and cancer. Our data suggest that these actions of tannic acid are mediated by its direct effect on ATE1, which regulates protein degradation and angiogenesis in vivo.

The birth and postnatal development of purinergic signalling

The purinergic signalling system is one of the most ancient and arguably the most widespread intercellular signalling system in living tissues. In this review we present a detailed account of the early developments and current status of purinergic signalling. We summarize the current knowledge on purinoceptors, their distribution and role in signal transduction in various tissues in physiological and pathophysiological conditions.

Characterization of functional P2X(1) receptors in mouse megakaryocytes

INTRODUCTION

Although accumulating evidence within the past 5 years strongly supports the importance of platelet P2X(1) receptors in hemostasis and thrombosis, P2X(1) receptors of platelet and/or its progenitor cell, megakaryocyte, have not been fully characterized. The aim of this study was to electrophysiologically and pharmacologically characterize the functional P2X(1) receptors on mouse megakaryocytes.

MATERIALS AND METHODS

The currents in response to nucleotides were examined using the patch-clamp whole-cell recording.

RESULTS

The agonist profile of megakaryocyte P2X(1) receptors was ATP>alpha,beta-methylene ATP>beta,gamma-methylene ATP. The P2X(1) receptors exhibited substantial monovalent as well as divalent cation permeability and the ratios of Na(+) to Cs(+) and Ca(2+) to Cs(+) permeability were 1 and 2.5, respectively. P2X receptor antagonists except suramin significantly inhibited the P2X(1) responses with an IC(50) values of 0.4 microM for pyridoxal-phosphate-6-azophenyl-2',4'-disulfonate (PPADS), 0.3 microM for 2',3'-O-(2,4,6-trinitophenyl)-adenosine 5'-triphosphate (TNP-ATP), 20 microM for reactive blue 2 (RB2), or 160 microM for 8,8'-(carbonylbis(imino-3,1-phenylene carbonylimino)bis(1,3,5-naphthalenetrisulfonic acid) (NF023), respectively. Suramin had no significant effect on the P2X(1) responses. In rat megakaryocytes, suramin similarly had no significant effect on the P2X(1) responses, but abolished the P2Y receptor-mediated responses, indicating that the suramin was active under present experimental condition.

CONCLUSIONS

These results provide the basic properties of mouse megakaryocyte P2X(1) receptors and would be helpful to examine the P2 receptor signaling in platelets and megakaryocytes.

Cellular Distribution and Functions of P2 Receptor Subtypes in Different Systems

This 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.

Autocrine action and its underlying mechanism of nitric oxide on intracellular Ca2+ homeostasis in vascular endothelial cells

The rise in cytosolic Ca(2+) concentration (Ca(2+)(i)) in vascular endothelial cells (ECs) activates the production and release of nitric oxide (NO). NO modifies Ca(2+)(i) homeostasis in many types of nonendothelial cells. However, its effect on endothelial Ca(2+)(i) homeostasis at basal and excited states remains unclear. In the present study, to elucidate the effect of NO on basal Ca(2+)(i), inositol 1,4,5-trisphosphate-induced Ca(2+)(i) release (IICR) was blocked by expressing an antisense against type-1 inositol 1,4,5-trisphosphate receptors or by microinjecting heparin to individual ECs, and the effects of NO that was released by and diffused from adjacent IICR-intact ECs were recorded. After ATP or bradykinin stimulation, IICR-inhibited ECs showed a marked reduction of basal Ca(2+)(i), which was abolished by N(G)-monomethyl-l-arginine monoacetate pretreatment. The reduction disappeared in sparsely seeded ECs. Exogenous NO gas mimicked the effect of ATP or bradykinin to reduce basal Ca(2+)(i). Blocking plasma membrane Ca(2+)-ATPase (PMCA), but not Na(+)-Ca(2+) exchange or sarcoplasmic/endoplasmic reticulum Ca(2+)-ATPase, suppressed the reduction, indicating that the reduction resulted from a NO-dependent potentiation of PMCA. To elucidate the effect of NO on elevated Ca(2+)(i), ATP-, bradykinin-, or thapsigargin-evoked Ca(2+)(i) response in the presence and absence of NO production was compared in adjacent IICR-intact ECs. NO was found to potentiate PMCA, which, in turn, greatly attenuated agonist-evoked Ca(2+)(i) elevation. NO also potentiated Ca(2+) influx, which markedly increased the sustained phase of Ca(2+)(i) elevation and possibly NO production. NO did not affect other Ca(2+)(i)-elevating and Ca(2+)(i)-sequestrating components. Thus, NO-dependent potentiation of PMCA is crucial for Ca(2+)(i) homeostasis over a wide Ca(2+)(i) range.

ATP activates DNA synthesis by acting on P2X receptors in human osteoblast-like MG-63 cells

In human osteoblast-like MG-63 cells, extracellular ATP increased [(3)H]thymidine incorporation and cell proliferation and synergistically enhanced platelet-derived growth factor- or insulin-like growth factor I-induced [(3)H]thymidine incorporation. ATP-induced [(3)H]thymidine incorporation was mimicked by the nonhydrolyzable ATP analogs adenosine 5'-O-(3-thiotriphosphate) and adenosine 5'-adenylylimidodiphosphate and was inhibited by the P2 purinoceptor antagonist suramin, suggesting involvement of P2 purinoceptors. The P2Y receptor agonist UTP and UDP and a P2Y receptor antagonist reactive blue 2 did not affect [(3)H]thymidine incorporation, whereas the P2X receptor antagonist pyridoxal phosphate-6-azophenyl-2',4-disulfonic acid inhibited ATP-induced [(3)H]thymidine incorporation, suggesting that ATP-induced DNA synthesis was mediated by P2X receptors. RT-PCR analysis revealed that MG-63 cells expressed P2X(4), P2X(5), P2X(6), and P2X(7), but not P2X(1), P2X(2), and P2X(3), receptors. In fura 2-loaded cells, not only ATP, but also UTP, increased intracellular Ca(2+) concentration, and inhibitors for several Ca(2+)-activated protein kinases had no effect on ATP-induced DNA synthesis, suggesting that an increase in intracellular Ca(2+) concentration is not indispensable for ATP-induced DNA synthesis. ATP increased mitogen-activated protein kinase activity in a Ca(2+)-independent manner and synergistically enhanced platelet-derived growth factor- or insulin-like growth factor I-induced kinase activity. Furthermore, the mitogen-activated protein kinase kinase inhibitor PD-98059 totally abolished ATP-induced DNA synthesis. We conclude that ATP increases DNA synthesis and enhances the proliferative effects of growth factors through P2X receptors by activating a mitogen-activated protein kinase pathway.

Ca2+ mobilization in bovine corneal endothelial cells by P2 purinergic receptors

PURPOSE

To characterize Ca2+ mobilization by P2 receptors in the bovine corneal endothelial cells (BCEC).

METHODS

Changes in intracellular Ca2+ ([Ca2+]i) were measured by fluorescence imaging of cultured and fresh BCEC cells loaded with the Ca2+-sensitive dye Fura-PE3. Relative rates of Ca2+ influx were measured employing Mn2+ as a surrogate for Ca2+.

RESULTS

Exposure of cultured cells to uridine 5'-triphosphate (UTP), 2-methyl-thio ATP (msATP) and ATP caused biphasic changes in [Ca2+]i consisting of a peak followed by a plateau phase. Based on the peak responses to 100 microM agonist, the magnitude of UTP responses were similar to that of ATP but greater than that of msATP or ADP. UTP and msATP stimulated Mn2+ influx following [Ca2+]i peak similar to that observed in response to cyclopiazonic acid (CPA), an inhibitor of ER Ca2+-ATPase. Under Ca2+-free conditions, peak responses were similar to those in the presence of external Ca2+, but reduced when the cells were pre-exposed to CPA. Reactive Blue-2 (RB2), inhibited msATP responses by 60.4 +/- 18.8% but UTP responses by only 10.6 +/- 9.5%. Repeated exposures to UTP or msATP reduced [Ca2+]i mobilization indicating homologous desensitization. Response to UTP was not affected by a prior exposure to msATP. However, response to msATP was reduced by a prior exposure to UTP indicating mixed heterologous desensitization. Fresh cells responded to UTP (50 microM) with temporal characteristics of [Ca2+]i mobilization similar to that of cultured cells.

CONCLUSION

BCEC express P2 receptors belonging to the P2Y subfamily. The emptying of the IP3-sensitive stores, leading to the initial peak in [Ca2+]i response, subsequently caused capacitative Ca2+ influx leading to the onset of the plateau phase. A significant homologous desensitization to UTP and msATP, selective heterologous desensitization between UTP and msATP, and selective inhibition by RB2 indicate the coexistence of multiple P2Y receptors.

Cyclic GMP inhibits cytoplasmic Ca2+ oscillation by increasing Ca2+-ATPase activity in rat megakaryocytes

The regulatory effects of cyclic GMP on purinoceptor-operated cytoplasmic Ca2+ oscillation of rat megakaryocytes were investigated by using whole-cell patch-clamp technique. ATP-induced oscillatory K+ currents though Ca2+-activated K+ channels (I(KCa)S) were depressed by pretreatment with the guanylate cyclase activator, sodium nitroprusside, and a stable membrane-permeable cGMP analogue, 8-bromo-cGMP. The inhibition by sodium nitroprusside was blocked by treatment with a cyclic nucleotide-dependent protein kinase inhibitor, N-[2-(methylamino)]-5-isoquinolinesulfonamide x HCl (H-8) (10 microM), but not by a selective cAMP-dependent-protein kinase inhibitor, Rp-cAMPS (100 microM). The oscillatory I(KCa) directly evoked by intracellular D-myo-inositol-trisphosphate (IP3) perfusion was also inhibited by the application of sodium nitroprusside. The inhibitory effect of sodium nitroprusside disappeared when the ATP-induced oscillatory I(KCa) was changed to a monophasic sustained I(KCa) current by inhibition of Ca2+-ATPase. These results suggested that cGMP depressed Ca2+ mobilization by improving Ca2+-ATPase activity by phosphorylation.

ATP release and contraction mediated by different P2-receptor subtypes in guinea-pig ileal smooth muscle

1. The present study was addressed to clarify the subtypes of P2-purinoceptor involved in ATP release and contraction evoked by alpha, beta-methylene ATP (alpha, beta-mATP) and other P2-agonists in guinea-pig ileum. 2. alpha, beta-mATP 100 microM produced a transient and steep contraction followed by ATP release from tissue segments. These maximum responses appeared with different time-courses and their ED50 values were 5 and 25 microM, respectively. The maximum release of ATP by alpha, beta-mATP was markedly reduced by 250 microM suramin, 30 microM pyridoxal-phosphate-6-azophenyl-2',5'-disulphonic acid (PPADS) and 30 microM reactive blue 2 (RB-2), P2-receptor antagonists. However, the contractile response was inhibited by suramin, tetrodotoxin and atropine, but not by PPADS and RB-2. 3. Although the contraction caused by alpha, beta-mATP was strongly diminished by Ca(2+)-removal and nifedipine, and also by tetrodotoxin and atropine at 0.3 microM, the release of ATP was virtually unaffected by these procedures. 4. UTP, beta, gamma-methylene ATP (beta, gamma-mATP) and ADP at 100 microM elicited a moderate release of ATP. The release caused by UTP was virtually unaffected by RB-2. However, these P2-agonists failed to elicit a contraction of the segment. 5. The potency order of all the agonists tested for the release of ATP was alpha, beta-mATP > UTP > beta, gamma-mATP > ADP. 6. In superfusion experiments with cultured smooth muscle cells from the ileum, alpha, beta-mATP (100 microM) enhanced the release of ATP 5 fold above the basal value. This evoked release was inhibited by RB-2. 7. These findings suggest that ATP release and contraction induced by P2-agonists such as alpha, beta-mATP in the guinea-pig ileum result mainly from stimulation of different P2-purinoceptors. P2Y-like purinoceptors on the smooth muscles and, probably, P2X-purinoceptors on cholinergic nerve terminals, respectively. However, the ATP release may also be mediated, in part, by P2U-receptors, because UTP caused RB-2-insensitive ATP release.

Dual effects of extracellular ATP on the muscarinic acetylcholine receptor-operated K+ current in guinea-pig atrial cells

Adenosine 5'-triphosphate (ATP) is stored in sympathetic and parasympathetic nerve terminals and co-released with norepinephrine and acetylcholine during nerve stimulation. In the heart in situ parasympathetic nerve is tonically stimulated and the activated muscarinic acetylcholine-receptor-operated K+ current (I(K,ACh)) plays an important role in the repolarization of the atrial action potential, the sinoatrial node automaticity and the atrioventricular conduction. In the present study, effects of extracellular ATP on the I(K,ACh) activated by carbachol or adenosine were examined in isolated guinea-pig atrial cells by use of the patch-clamp technique. ATP (10 microM) per se produced a transient activation of I(K,ACh) in atrial cells held at -40 mV. When I(K,ACh) was preactivated by 1 microM carbachol or 10 microM adenosine, ATP (1-100 microM) produced a transient increase followed by a sustained decrease of the current. These ATP-induced biphasic changes of I(K,ACh) were abolished by suramin (100 microM) or reactive blue-2 (30 microM), but not by theophylline (500 microM), indicating the involvement of P2 purinoceptors. ATP also enhanced and then partially reversed the action potential shortening induced by carbachol or adenosine in current-clamped atrial cells. Extracellular ATP did not increase but decreased the openings of the single K(ACh) channel that were recorded by use of a pipette solution containing 1 microM carbachol in the cell-attached mode. Thus, P2 purinoceptor stimulation produces dual effects of ATP on the pre-activated I(K,ACh) and may modulate the chronotropic and inotropic responses during autonomic nerve stimulation.

Kinetic characteristics of thrombin receptor-mediated responses in rat megakaryocytes

Kinetic characteristics of thrombin receptor-mediated responses on rat megakaryocytes were examined by the use of the perforated patch clamp combined with the rapid drug exchange system termed the 'Y-tube method'. The application of thrombin evoked repetitive Ca(2+)-activated K+ current (IKCa) in a concentration-dependent manner. The characteristic features for thrombin-induced response compared with purinoceptor-induced response were the long latency, long washout time and fast desensitization. The similar IKCa as thrombin was induced by trypsin. Thrombin- and trypsin-induced IKCa were both inhibited by the protease inhibitor, SBTI, and the washout time for thrombin was markedly shortened (7.4 +/- 2.2 s) when thrombin was washed out by a solution containing soybean trypsin inhibitor. A synthetic thrombin receptor agonist peptide induced IKCa oscillation with shorter latency than thrombin.

Differential modulation of voltage-activated conductances by intracellular and extracellular cyclic nucleotides in leech salivary glands

1. Two-electrode voltage clamp was used to study the effects of adenosine 3':5'-cyclic monophosphate (cyclic AMP) and guanosine 3':5'-cyclic monophosphate (cyclic GMP) on voltage-dependent ion channels in salivary gland cells of the leech, Haementeria ghilianii. 2. Intracellular cyclic AMP specifically blocked delayed rectifier K+ channels. This was shown by use of 3-isobutyl-1-methylxanthine (IBMX, a phosphodiesterase inhibitor), forskolin (an activator of adenylyl cyclase) and intracellular injection of cyclic AMP and its dibutyryl and 8-bromo analogues. Cyclic AMP appeared to be the second messenger for the putative neuroglandular transmitter, 5-hydroxytryptamine. 3. Intracellular injection of cyclic GMP specifically potentiated high-voltage-activated (HVA) Ca2+ current and the effect was mimicked by zaprinast, an inhibitor of cyclic GMP-dependent phosphodiesterase. 4. Extracellularly, cyclic GMP and cyclic AMP specifically decreased the amplitude and increased the rate of inactivation of HVA Ca2+ current. These effects of the cyclic nucleotides are identical to those known for extracellular ATP, which activates a presumed purinoceptor. The pyrimidine nucleotide, UTP, was almost equipotent to ATP (threshold dose < 10(-6) M), indicative of a vertebrate-type nucleotide receptor. However, suramin (5 x 10(-5) M), a non-specific P2-receptor antagonist, failed to block the effects of 5 x 10(-6) M ATP (higher suramin doses could not be reliably tested because of the depolarization and increase in membrane conductance produced by the drug). 5. Activation of the putative purinoceptor by ATP did not affect inward rectifier Na+/K+ current which is known to be potentiated by intracellular cyclic AMP and reduced by intracellular cyclic GMP. 6. The preparation may provide a useful model for study of nucleotide actions, and interactions, in channel modulation. It has technical advantages such as large cells (1200 microns in diameter) which lack intercellular coupling and may be individually dissected for biochemical studies.

Biological actions of purines on rat megakaryocytes: potentiation by adenine of the purinoceptor-operated cytoplasmic Ca2+ oscillation

We have found that adenine enhanced the purinoceptor-operated cytoplasmic Ca2+ oscillation in rat megakaryocytes at submillimolar concentrations. Guanine and other nucleic acid bases had no effect on this system. Adenine enhanced the reaction intensity but had no effect on the threshold concentration of ATP to evoke the oscillation.