Expression and characterization of purinergic receptors in rat middle meningeal artery-potential role in migraine

The dura mater and its vasculature have for decades been central in the hypothesis of migraine and headache pathophysiology. Although recent studies have questioned the role of the vasculature as the primary cause, dural vessel physiology is still relevant in understanding the complex pathophysiology of migraine. The aim of the present study was to isolate the middle meningeal artery (MMA) from rodents and characterize their purinergic receptors using a sensitive wire myograph method and RT-PCR. The data presented herein suggest that blood flow through the MMA is, at least in part, regulated by purinergic receptors. P2X1 and P2Y6 receptors are the strongest contractile receptors and, surprisingly, ADPβS caused contraction most likely via P2Y1 or P2Y13 receptors, which is not observed in other arteries. Adenosine addition, however, caused relaxation of the MMA. The adenosine relaxation could be inhibited by SCH58261 (A2A receptor antagonist) and caffeine (adenosine receptor antagonist). This gives one putative molecular mechanism for the effect of caffeine, often used as an adjuvant remedy of cranial pain. Semi-quantitative RT-PCR expression data for the receptors correlate well with the functional findings. Together these observations could be used as targets for future understanding of the in vivo role of purinergic receptors in the MMA.

[Effects of purine nucleotide on the expressions of FSH and LH and the ultrastructure of endocrine cells in the pituitary gland of heroin-addicted male rats]

OBJECTIVE

To investigate the effects of purine nucleotide on the expressions of follicle-stimulating hormone (FSH) and luteotrophic hormone (LH) and the ultrastructures of the distal somatotrophic and gonadotrophic cells in the pituitary gland of heroin-addicted and -withdrawal rats.

METHODS

Ninety-two male Wistar rats were randomly divided into a control group (ip saline for 14 d), a nucleotide group (ip AMP and GMP for 10 d), a heroin group (ip heroin for 10 d), a heroin + nucleotide group (ip AMP and GMP + heroin for 10 d), a 3 d withdrawal group (ip heroin for 10 d and killed at 14 d), a 9 d withdrawal group (ip heroin for 10 d and killed at 20 d), a 3 d nucleotide group (ip nucleotide for 3 d after 10 d heroin administration and killed at 14 d), and a 9 d nucleotide group (ip nucleotide for 9 d after 10 d heroin administration and killed at 20 d). Changes in the mRNA expressions of FSH and LH in the pituitary gland of the rats were analyzed by semi-quantitative RT-PCR, and alterations in the ultrastructures of the distal somatotrophic and gonadotrophic cells were observed under the microscope.

RESULTS

The expression of FSH mRNA was significantly increased in the nucleotide, heroin + nucleotide, 3 d nucleotide and 9 d nucleotide groups (0.099 +/- 0.018, 0.177 +/- 0.046, 0.151 +/- 0.030 and 0.184 +/- 0.028) as compared with the control group (0.045 +/- 0.009) (P < 0.01); and so was that of LH mRNA in the heroin + nucleotide, 3 d nucleotide and 9 d nucleotide groups (0.950 +/- 0.169, 0.990 +/- 0.171 and 0.960 +/- 0.147) in comparison with the control group (0.700 +/- 0.099) (P < 0.01). In the heroin group, the nuclei of the distal somatotrophic and gonadotrophic cells exhibited morphological abnormality, unclear membrane, slightly pyknotic matrix, marginal and agglutinated heterochromatin, dilated rough endoplasmic reticula, swollen mitochondria, broken and vacuolated cristae in the cytoplasm, obviously decreased number of secretory granules, and myelin bodies in some cells. However, the heroin + nucleotide group showed no significant changes in the ultrastructures of somatotrophic and gonadotrophic cells compared with the control group.

CONCLUSION

Short-term use of heroin does not obviously affect the expressions of FSH and LH mRNA in the pituitary gland of rats, while heroin + nucleotide, or nucleotide following heroin withdrawal can enhance their expressions significantly. Heroin damages the ultrastructures of the distal somatotrophic and gonadotrophic cells in the pituitary gland of male rats, and purine nucleotide can diminish or inhibit this damage.

A comparative study of the inhibitory effects of purine nucleotides and carboxyatractylate on the uncoupling protein-3 and adenine nucleotide translocase

Uncoupling proteins (UCPs) mediate fatty acid-induced proton cycling in mitochondria, which is stimulated by superoxide and inhibited by GDP. Fatty acid anions can also be transported by adenine nucleotide translocase (ANT), thus resulting in the uncoupling of oxidative phosphorylation. In the present work, an attempt was made to distinguish between the protonophoric activity of UCP3 and that of ANT using inhibition analysis. This study was carried out using mitochondria from skeletal muscles of hibernating Yakut ground squirrel, which have a significant level of UCP3 mRNA. We found that millimolar concentrations of GDP, which is considered to be a specific inhibitor of UCPs, slightly recoupled the mitochondrial respiration and restored the membrane potential. Addition of the specific ANT inhibitor CAT (carboxyatractylate), in micromolar concentration, prior to GDP prevented its recoupling effect. Moreover, GDP and ADP exhibited a competitive kinetic behavior with respect to ANT. In brown adipose tissue, CAT did not prevent the UCP1-iduced increase in chloride permeability and the inhibitory effect of GDP, thus confirming the inability of CAT to affect UCP1. These results allow us to conclude that the recoupling effect of purine nucleotides on skeletal muscle mitochondria of hibernating ground squirrels can be explained by interaction of the nucleotides with ANT, whereas UCP3 is not involved in the process.

[Effects of heroin and purine nucleotide compensation on neutral alpha-glucosidase in rat epididymides]

OBJECTIVE

To study the changes of neutral alpha-glucoside activity in the epididymis of heroin-dependent and heroin-withdrawal rats, and to investigate the effects of intervention with purine nucleotide (AMP and GMP).

METHODS

Eighty Wistar rats were randomly divided into 8 groups of equal number, control, nucleotide, heroin, heroin + nucleotide, 3 d withdrawal, 9 d withdrawal, 3 d nucleotide (nucleotide administrated for 3 days after heroin withdrawal) and 9 d nucleotide (nucleotide administrated for 9 days after heroin withdrawal). Neutral alpha-glucosidase activity in the epididymis was detected in each group of rats.

RESULTS

Compared with the control group, neutral alpha-glucoside activity was markedly decreased in the heroin group (P < 0.05), and also in the 3 d and 9 d withdrawal groups, although with no significant differences (P > 0.05).

CONCLUSION

Heroin reduces neutral alpha-glucoside activity in the epididymis of rats, and this effect may continue for some time after drug withdrawal, while purine nucleotide can keep neutral alpha-glucosidase activity in a relatively stable state.

Complete deficiency of 5'-nucleotidase activity in Escherichia coli leads to loss of growth on purine nucleotides but not of their excretion

Escherichia coli has many periplasmic phosphatase activities. To test whether it can take up and excrete purine nucleotides, we attempted to completely disrupt periplasmic 5'-nucleotidase activity. A 5'-nucleotidase activity was induced in ushA knockout mutant cells, which lack major 5'-nucleotidase activity, when they were grown with purine nucleotides as the sole carbon source. Using DNA macroarrays to compare global gene expression in wild-type and ushA knockout mutant cells cultured with IMP or GMP as the sole carbon source, we identified two genes that were induced in the ushA knockout mutant cells and encoded signal sequence needed for secretion. One of the genes, aphA, encoded a 5'-nucleotidase activity and was induced by IMP or inosine. An ushA aphA double knockout mutant was shown to be unable to grow on purine nucleotides as the sole carbon source. To investigate the excretion of purine nucleotides, we constructed an ushAaphA double knockout mutant of an inosine-producing strain and found that it accumulated IMP in the medium. In addition, when the guaBA operon was introduced into the ushAaphA double knockout IMP producer, GMP was released into the medium. These observations imply the existence of efflux activity for purine nucleotides in E. coli.

Human DEAD-box ATPase DDX3 shows a relaxed nucleoside substrate specificity

Human DDX3 (hDDX3) is a DEAD-box protein shown to possess RNA-unwinding and adenosine triphosphatase (ATPase) activities. The hDDX3 protein has been implicated in nuclear mRNA export, cell growth control, and cancer progression. In addition, a role of this protein in the replication of human immunodeficiency virus Type 1 and in the pathogenesis of hepatitis C virus has been recently proposed. Its enzymological properties, however, are largely unknown. In this work, we characterized its ATPase activity. We show that hDDX3 ATPase activity is stimulated by various ribo- and deoxynucleic acids. Comparative analysis with different nucleoside triphosphate analogs showed that the hDDX3 ATPase couples high catalytic efficiency to a rather relaxed substrate specificity, both in terms of base selection and sugar selection. In addition, its ability to recognize the L-stereoisomers of both 3' deoxy- and 2',3' dideoxy-ribose, points to a relaxed stereoselectivity. On the basis of these results, we hypothesize the presence of structural determinants on both the base and the sugar moieties, critical for nucleoside binding to the enzyme. Our results expand the knowledge about the DEAD-box RNA helicases in general and can be used for rational design of selective inhibitors of hDDX3, to be tested as potential antitumor and antiviral agents.

Temperature-dependent effects of cadmium and purine nucleotides on mitochondrial aconitase from a marine ectotherm, Crassostrea virginica: a role of temperature in oxidative stress and allosteric enzyme regulation

Temperature and heavy metals such as cadmium (Cd) are important environmental stressors that can strongly affect mitochondrial function of marine poikilotherms. In this study, we investigated the combined effects of temperature (20 degrees C and 30 degrees C) and Cd stress on production of reactive oxygen species (ROS) and oxidative stress in a marine poikilotherm Crassostrea virginica (the eastern oyster) using mitochondrial aconitase as a sensitive biomarker of oxidative damage. We also assessed potential involvement of mitochondrial uncoupling proteins (UCPs) in antioxidant protection in oyster mitochondria using purine nucleotides (GDP, ATP and ADP) as specific inhibitors, and free fatty acids as stimulators, of UCPs. Our results show that exposure to Cd results in elevated ROS production and oxidative damage as indicated by aconitase inactivation which is particularly pronounced at elevated temperature. Unexpectedly, oyster mitochondrial aconitase was inhibited by physiologically relevant levels of ATP (IC(50)=1.93 and 3.04 mmol l(-1) at 20 degrees C and 30 degrees C, respectively), suggesting that allosteric regulation of aconitase by this nucleotide may be involved in regulation of the tricarboxylic acid flux in oysters. Aconitase was less sensitive to ATP inhibition at 30 degrees C than at 20 degrees C, consistent with the elevated metabolic flux at higher temperatures. ADP and GDP also inhibited mitochondrial aconitase but at the levels well above the physiological concentrations of these nucleotides (6-11 mmol l(-1)). Our study shows expression of at least three UCP isoforms in C. virginica gill tissues but provides no indication that UCPs protect mitochondrial aconitase from oxidative inactivation in oysters. Overall, the results of this study indicate that temperature stress exaggerates toxicity of Cd leading to elevated oxidative stress in mitochondria, which may have important implications for survival of poikilotherms in polluted environments during seasonal warming and/or global climate change, and suggest a novel temperature-dependent mechanism of allosteric regulation of TCA flux in oyster mitochondria.

Synthesis and biological properties of new phosmidosine analogs having an N-acylsulfamate linkage

A new phosmidosine analog 10, in which the proline and 8-oxoadenosine moieties were linked by an N-acyl sulfamate linkage, was successfully synthesized by the sulfamoylation of an 8-oxoadenosine derivative 5 followed by coupling with an L-proline derivative 8. An L-alanine-substituted derivative 13 and its derivative 14 without the alanyl residue were also synthesized. The morphological reversion activity of these synthetic compounds in v-src(ts) NRK cells and their antitumor activity in L1210 and KB cells were studied. As the result, neither L-proline- nor L-alanine-substituted phosmidosine analogs 10 and 13 showed any antitumor activity. Contrary to these results, the derivative 14 lacking the amino acid residue showed potent antitumor activities against cancer cells.

Uncoupling proteins: a role in protection against reactive oxygen species--or not?

A physiological function of the original uncoupling protein, UCP1, is well established: UCP1 is the molecular background for nonshivering thermogenesis. The functions of the "novel" UCPs, UCP2 and UCP3, are still not established. Recent discussions imply that all UCPs may play a role in protection against reactive oxygen species (ROS). Here we examine critically the evidence that UCP1, UCP2 and UCP3 are stimulated by ROS (superoxide) or ROS products (4-hydroxy-2-nonenal), and that the UCPs actually diminish oxidative damage. We conclude that, concerning UCP1, it is unlikely that it has such a role; concerning UCP2/UCP3, most evidence for physiologically significant roles in this respect is still circumstantial.

[Effects of exogenerous nucleotides on the apoptosis of intestinal epithelial cells IEC-6]

OBJECTIVE

To investigate the effects of exogenous nucleotides on apoptosis of a normal rat small intestinal epithelial cell line, IEC-6.

METHODS

Cultured IEC-6 cells were treated by four kinds of monophosphate nucleotides and their mixture prepared according to their composition in human milk, then the cell apoptosis was determined by flow cytometry measurement, morphologic characterization, and electron-microscope observation.

RESULTS

IEC-6 cells treated with AMP or GMP showed a apotosis peak in flow cytometry measurement, but only AMP produce typical apoptosis characteristics in electron-microscope observation. Pyrimidine nucleotides (UMP and CMP)and nucleotides mixture could not induce apoptosis. However, UMP could significantly eliminate the apoptosis-inducing effects of AMP or GMP.

CONCLUSION

Purine nucleotides induce apoptosis of IEC-6, inducing effects of purine nucleotides. pyrimidine nucleotides UMP could abolish the apoptosis-inducing effects of purine nucleotides.

Synthesis of a biotin-conjugate of phosmidosine O-ethyl ester as a G1 arrest antitumor drug

This paper deals with the synthesis of a stable biotin-phosmidosine conjugate molecule 3 that is required for isolation of biomolecules that bind to phosmidosine (1). It was found that introduction of a biotin residue into the 6-N position of phosmidosine could be carried out by reaction of an N7-Boc-7,8-dihydro-8-oxoadenosine derivative 13 with phenyl chloroformate followed by displacement with a diamine derivative 6 along with the simultaneous removal of the Boc group and one of the two phenoxycarbonyl groups and the successive condensation with an N-tritylated biotin derivative 5. The condensation of an N-prolylphosphorodiamidite derivative 4 with an appropriately protected 7,8-dihydro-8-oxoadenosine derivative 17 having the biotin residue gave the coupling product 18, which was deprotected to give the biotin-phosmidosine (O-ethyl ester) conjugate 3.

Autoinhibition of transmitter release from PC12 cells and sympathetic neurons through a P2Y receptor-mediated inhibition of voltage-gated Ca2+ channels

Although feedback inhibition of noradrenaline release by coreleased nucleotides is a well known phenomenon, it remained unclear which P2 receptor subtypes and associated signalling cascades may be involved. In the rat pheochromocytoma cell line PC12, 2-methylthio-ADP reduced noradrenaline release triggered by K+ depolarization more potently than ADP and ATP, whereas UDP or UTP failed to do so. The inhibition by ADP was abolished by pertussis toxin and antagonized by reactive blue 2, 2-methylthio-AMP, and AR-C69931MX, but not by suramin. AR-C69931MX acted as a competitive antagonist with an apparent affinity of 2 nm, but did not alter noradrenaline release, when PC12 cells were continuously superfused. However, when the superfusion was halted during K+ depolarization, release was significantly reduced and this inhibition was attenuated by AR-C69931MX, thus revealing ongoing autoinhibition. Rises in cellular cyclic AMP did not alter depolarization-evoked release nor its reduction by ADP, even though the nucleotide did inhibit cyclic AMP accumulation. ADP and the direct Ca2+ channel blocker Cd2+ inhibited voltage-activated Ca2+ currents, but not ATP-induced currents, and both agents reduced K+-evoked, but not ATP-evoked, release. Hence, if voltage-gated Ca2+ channels do not contribute to stimulation-evoked release, ADP fails to exert its inhibitory action. In primary cultures of rat sympathetic neurons, ADP also reduced Ca2+ currents and K+-evoked noradrenaline release, and AR-C69931MX acted again as competitive antagonist with an apparent affinity of 3 nm. These results show that P2Y12 receptors mediate an autoinhibition of transmitter release from PC12 cells and sympathetic neurons through an inhibition of voltage-gated Ca2+ channels.

Broad specificity of human phosphoglycerate kinase for antiviral nucleoside analogs

Nucleoside analogs used in antiviral therapies need to be phosphorylated to their tri-phospho counterparts in order to be active on their cellular target. Human phosphoglycerate kinase (hPGK) was recently reported to participate in the last step of phosphorylation of cytidine L-nucleotide derivatives [Krishnan PGE, Lam W, Dutschman GE, Grill SP, Cheng YC. Novel role of 3-phosphoglycerate kinase, a glycolytic enzyme, in the activation of L-nucleoside analogs, a new class of anticancer and antiviral agents. J Biol Chem 2003;278:36726-32]. In the present work, we extended the enzymatic study of human PGK specificity to purine and pyrimidine nucleotide derivatives in both D- and L-configuration. Human PGK demonstrated catalytic efficiencies in the 10(4)-10(5)M(-1)s(-1) range for purine ribo-, deoxyribo- and dideoxyribonucleotide derivatives, either in D- or L-configuration. In contrast, it was poorly active with natural pyrimidine D-nucleotides (less than 10(3)M(-1)s(-1)). Pyrimidine L-enantiomers, which are promising therapeutic analogs against B hepatitis, were 2-25 times better substrates than their D-counterparts. The broad specificity of substrate of human PGK suggests that this enzyme may be involved in the cellular activation of several antiviral nucleoside analogs including dideoxyinosine, acyclovir, L-2'-deoxycytosine and L-2'-deoxythymidine.

Improved antiviral activity of the aryloxymethoxyalaninyl phosphoramidate (APA) prodrug of abacavir (ABC) is due to the formation of markedly increased carbovir 5'-triphosphate metabolite levels

The anti-human immunodeficiency virus (HIV) activity of abacavir (ABC; 1-(1S,4R)-4-[2-amino-6-(cyclopropylamino)-9H-purin-9-yl]-2-cyclopentene-1-methanol) could be markedly enhanced by administering the aryloxymethoxyalaninyl phosphoramidate prodrug derivative of ABC (pro-ABC-MP) to virus-infected cell cultures. Metabolic studies with radiolabeled ABC and pro-ABC-MP in human T-lymphocyte and primary macrophage cell cultures revealed a significantly increased delivery of the activated (phosphorylated) metabolite of ABC (ABC-MP) by pro-ABC-MP, and the concomittant appearance of markedly higher intracellular levels of carbovir 5'-triphosphate (CBV-TP), which represents the eventual antivirally active metabolite of ABC. The intracellular amounts of ABC-MP and appearance of CBV-TP closely correlated with the extracellular pro-ABC-MP concentrations that were administered to the cell cultures within a concentration range between 0.5 and 100 microM. The highest amounts of CBV-TP were observed within 6-24 h after drug administration. The improved delivery of ABC-MP and metabolic conversion to CBV-TP explain the markedly enhanced antiviral activity of the prodrug of ABC, and warrant further exploration of this prodrug technology on ABC and related compounds to further enhance and optimize their antiviral efficacy.

Effects of purinenucleotide analogues on microtubule assembly

This minireview summarizes the syntheses of various purinenucleotide analogues and their effects on microtubule (Mt) assembly. 27 analogues were so far synthesized and, together with 3 analogues commercially available (ITP, XTP and dGTP), their effects on Microtubule assembly were investigated. The positions C2, C6, C8, and ribose moiety of purine nucleotides were modified or substituted. It was found that the microenvironments of the purine base and ribose moiety are important for the nucleotides to support Mt assembly. Introduction of amino group into position C2 of ATP, formation of 2-amino ATP, caused Mt assembly substantially. 2-Amino deoxy ATP and deoxy GTP are more potent than GTP in supporting assembly. The introduction of reactive thiol group into C6 (6-SH-GTP) largely reduces the activity of the analogue to support assembly. However, sequestering reactivity of the thiol group by association with methyl group largely recovers the ability of the analogue to promote assembly. Free rotation of the glycosidic linkage was found to be also innevitable in promoting assembly, as the introduction of sulfur atom between C8 of the purine base and C2' of the ribose moiety (formation of 8,2'-S-cyclo purine nucleotides) caused total inhibition. Purinenucleoside triphosphate supports assembly better than GTP but the deoxy-type analogues are totally inhibitory. 2-Amino-8-hydroxy ATP and other analogues support assembly much better than does GTP. However, their diphosphate analogues are totally incapable of supporting assembly. Introduction of a bulky fluorescent probes into C3' can be made to visualize the fluorescent signal in assembled Mts. Together with the suggestions proposed from electron chrystallography of zinc-induced tubulin sheets, interactions of the purine base and ribose moieties with surrounding amino acid residues are discussed.

Synthesis of chemically stabilized phosmidosine analogues and the structure--activity relationship of phosmidosine

Phosmidosine is known to have potent antitumor activity and the unique property of stopping cell growth at the G(1) phase in the cell cycle. However, this natural product having N-prolylphosphoramidate and O-methyl ester linkages on the 5'-phosphoryl residue is unstable under basic conditions and even during the chemical synthesis due to its inherent methyl transfer activity. To find stable derivatives of phosmidosine, a variety of phosmidosine analogues 1a-d replaced by longer alkyl groups in place of the methyl group on the phosphoramidate linkage were synthesized by reaction of alkyl N-(N-tritylprolyl)phosphorodiamidite derivatives 7a-d with an 8-oxoadenosine derivative 4 protected with acid-labile protecting groups. Consequently, the O-ethyl ester derivative 1b was found to be sufficiently stable in aqueous solution. When the prolyl group was replaced by other aminoacyl moieties, the reaction of N-tritylaminoacylamide derivatives 25a-d with an appropriately protected 8-oxoadenosine 5'-(ethyl phosphoramidite) derivative 9 gave better results than the above coupling reaction. A phosphoramidothioate derivative 17 and several simple compounds such as 11, 13, and 15 lacking partial structures of phosmidosine were also synthesized. The antitumor activities of these modified analogues were extensively studied to clarify the structure-activity relationship of phosmidosine. As a result, the two diastereoisomers of longer alkyl-containing phosmidosine analogues both proved to have similar antitumor activities. Replacement of l-proline with other l-amino acids or d-proline resulted in considerable decrease of the antitumor activity. The non-nucleotidic materials 13 did not show any antitumor activity, but a simple core compound of 11 exhibited weak cytotoxicity. The phosphoramidothioate derivative 17 maintained essentially a similar antitumor activity, but the efficiency decreased slightly.

Mechanically evoked reflex electrogenic chloride secretion in rat distal colon is triggered by endogenous nucleotides acting at P2Y1, P2Y2, and P2Y4 receptors

Mechanical activation of the mucosal lining of the colon by brush stroking elicits an intestinal neural reflex and an increase in short circuit current (Isc) indicative of electrogenic chloride ion transport. We tested whether endogenous nucleotides are physiologic regulators of mucosal reflexes that control ion transport. The brush stroking-evoked Isc response in mucosa and submucosa preparations (M-SMP) of rat colon was reduced by the P2Y1 receptor (R) antagonist 2'deoxy-N6-methyl adenosine 3',5'-diphosphate diammonium salt (MRS 2179) and further blocked by tetrodotoxin (TTX). M-SMP Isc responses to serosal application of the P2Y1 R agonist 2-methylthioadenosine-diphosphate (2MeSADP) or the P2Y2/P2Y4 R agonist 5'uridine-triphosphate (UTP) were reduced but not abolished by TTX. The potency profile of nucleotides for increasing Isc was 5'adenosine-triphosphate (ATP; effective concentration at half maximal response [EC50] 0.65 x 10(4) M) congruent with UTP (EC50 1.0 x 10(-4) M) congruent with 2MeSADP (EC50 = 1.60 x 10(-4) M). Mucosal touch and distention-induced Ca2+ transients in submucous neurons were reduced by apyrase and prevented by blocking the P2Y1 R with MRS 2179 and TTX; denervation of the mucosa. It did not occur by touching a ganglion directly. 2MeSADP Ca2+ responses occurred in subsets of neurons with or without substance P (SP) responses. The potency profile of nucleotides on the neural Ca2+ response was 2MeSADP (5 x 10(-7) M) > UTP (6 x 10(-6) M) > ATP (9 x 10(-5) M). The expression of P2Y R immunoreactivity (ir) in nerve cell bodies was in the order of P2Y1 R > P2Y4 R >> P2Y2 R. P2Y1R ir occurred in the cell somas of more than 90% of neuronal nitric oxide synthase, vasoactive intestinal peptide (VIP), calretinin, or neuropeptide Y (NPY)-ir neurons, 78% of somatostatin neurons, but not in calbindin or SP neurons. P2Y2 R ir was expressed in a minority of SP, VIP, NPY, vesicular acetylcholine transporter, and calcitonin gene-related peptide-ir varicose fibers (5-20%) and those surrounding calbindin (5-20%) neurons. P2Y4 ir occurred mainly in the cell somas of 93% of NPY neurons. Reverse transcriptase polymerase chain reaction of the submucosa demonstrated mRNA for P2Y1R, P2Y2, P2Y4, P2Y6, and P2Y12 Rs. Expression of P2Y1, P2Y2, and P2Y4 protein was confirmed by western blots. In conclusion, endogenous nucleotides acting at P2YRs transduce mechanically evoked reflex chloride ion transport in rat distal colon. Nucleotides evoke reflexes by acting primarily at postsynaptic P2Y1 Rs and P2Y4 R on VIP+/NPY+ secretomotor neurons, at P2Y2 Rs on no more than 2% of VIP+ secretomotor neurons, and 2Y2 Rs mainly of extrinsic varicose fibers surrounding putative intrinsic primary afferent and secretomotor neurons. During mucosal mechanical reflexes, it is postulated that P2Y1 R, P2Y2 R, and P2Y4 R are activated by endogenous ATP, UTP, and 5'uridine-diphosphate.

Synthesis and biological properties of stable phosmidosine analogs

Phosmidosine and a variety of its analogs were synthesized by reaction of N-diisopropyl-N'-(N tritylaminoacyl)phosphorodiamidite derivatives with appropriately protected 8-oxoadenosine derivatives. It was found that replacement of the methyl group of the N-acylphosphoramidate linkage with longer alkyl groups resulted in significant stabilization of the ester linkage. Among the phosmidosine analogs synthesized, the O-ethyl derivative was easily synthesized and was found to be sufficiently stable under acidic and neutral conditions. These stable phosmidosine analogs exhibited similar antitumor activities against several cancer cell lines. The structure-activity relationship is also discussed.

Differential control of cell cycle, proliferation, and survival of primary T lymphocytes by purine and pyrimidine nucleotides

Purine and pyrimidine nucleotides play critical roles in DNA and RNA synthesis as well as in membrane lipid biosynthesis and protein glycosylation. They are necessary for the development and survival of mature T lymphocytes. Activation of T lymphocytes is associated with an increase of purine and pyrimidine pools. However, the question of how purine vs pyrimidine nucleotides regulate proliferation, cell cycle, and survival of primary T lymphocytes following activation has not yet been specifically addressed. This was investigated in the present study by using well-known purine (mycophenolic acid, 6-mercaptopurine) and pyrimidine (methotrexate, 5-fluorouracil) inhibitors, which are used in neoplastic diseases or as immunosuppressive agents. The effect of these inhibitors was analyzed according to their time of addition with respect to the initiation of mitogenic activation. We showed that synthesis of both purine and pyrimidine nucleotides is required for T cell proliferation. However, purine and pyrimidine nucleotides differentially regulate the cell cycle since purines control both G(1) to S phase transition and progression through the S phase, whereas pyrimidines only control progression from early to intermediate S phase. Furthermore, inhibition of pyrimidine synthesis induces apoptosis whatever the time of inhibitor addition whereas inhibition of purine nucleotides induces apoptosis only when applied to already cycling T cells, suggesting that both purine and pyrimidine nucleotides are required for survival of cells committed into S phase. These findings reveal a hitherto unknown role of purine and pyrimidine de novo synthesis in regulating cell cycle progression and maintaining survival of activated T lymphocytes.

Development and application of bioprobes for Mammalian cell cycle analyses

In this review, I have mainly described the cell cycle inhibitors isolated from microbial metabolites. Once the molecular target of the inhibitor is determined, the inhibitor can be used as bioprobe to dissect the diverse aspect of biological functions in chemical biology research. Reveromycin A and phosmidosine inhibited the protein synthesis of mammalian cells and arrested the cell cycle at G1 phase. Lucilactaene arrested cells at G1 phase through restoration of mutant p53. Tryprostatin A inhibited the microtubule polymerization by interfering with the interaction between tubulin and microtubule associating protein. On the contrary, cyclotryprostatin D, structurally related to tryprostatin A, enhanced the tubulin polymerization. Terpendole E inhibited the motor activity of mitotic kinesin, Eg5 and induced monoastral spindle in M phase.

Adenosine 5'-triphosphate (ATP) is an excitatory cotransmitter with noradrenaline to the smooth muscle of the rat prostate gland

1. This study investigated whether adenosine 5'-triphosphate (ATP) is involved in neurotransmission to the rat prostate gland. 2. Fluorescence immunohistochemistry carried out on formaldehyde-fixed and frozen sections of rat prostate showed immunoreactivity for the P2X(1)-receptor in the fibromuscular stroma surrounding the secretory acini but not in the glandular epithelium. P2X(2)-, P2X(3)-, P2X(4)- and P2X(7)-receptors were immunonegative in the rat prostate stroma. Double-staining procedures showed P2X(1)-receptor immunoreactivity to be colocalized with alpha-actin immunoreactivity. 3. Isolated organ bath studies investigated whether drugs, which modify purinergic mechanisms, are able to affect contractility of the rat prostate gland. Suramin (100 micro M) and alphabetamethylene ATP (10 micro M) inhibited contractile responses to trains of electrical-field stimulation (70 V, 0.5 ms, 0.1-2 Hz) in the absence and presence of prazosin (300 nM). Responses to 5-20 Hz were unaffected by suramin or alphabetamethylene ATP. 4. Exogenous application of ATP analogues to unstimulated isolated preparations of rat prostate produced concentration-dependent suramin (100 micro M) sensitive transient contractions with a relative order of potency: alphabetamethylene ATP>betagammamethylene ATP>ATP. 5. Adenosine and adenosine 5'-monophosphate (AMP) did not produce contractile responses. 6. These results suggest that P2X(1)-receptors for ATP, which mediate contractions are present in the fibromuscular stroma of the rat prostate. The relative order of potency of ATP analogues in producing contractions of the rat prostate is consistent with the activation of P2X(1)-receptors. Inhibition by suramin and alphabetamethylene ATP of electrically evoked nerve-mediated contractions of the rat prostate implies that ATP contributes to this contractile response and is therefore a cotransmitter with noradrenaline during low-frequency stimulation.

The A167Y mutation converts the herpes simplex virus type 1 thymidine kinase into a guanosine analogue kinase

The thymidine (dThd) kinase (TK) encoded by herpes simplex virus type 1 (HSV-1) is not only endowed with dThd kinase, but also with thymidylate (dTMP) kinase and 2'-deoxycytidine (dCyd) kinase (dCK) activity. HSV-1 TK also recognizes a variety of antiherpetic guanine nucleoside analogues such as acyclovir (ACV), ganciclovir (GCV), lobucavir (LBV), penciclovir (PCV), and others (i.e., A5021). Site-directed mutagenesis of the highly conserved Ala-167 to Tyr in HSV-1 TK completely abolished TK, dTMP-K, and dCK activity, but maintained ACV-, GCV-, LBV-, PCV-, and A5021-phosphorylating capacity. A variety of 5-substituted pyrimidine nucleoside substrates, but also a number of selective HSV-1 TK inhibitors structurally related to thymine lost significant binding affinity for the mutant enzyme and did not markedly compete with GCV phosphorylation by the mutant enzyme. These findings could be explained by computer-assisted modeling data that revealed steric hindrance of the pyrimidine ring in the HSV-1 TK active site by the large 4-hydroxybenzyl ring of 167-Tyr, while the positioning of the purine ring of guanine-based HIV-1 TK substrates in the active site was kept virtually unaltered. Surprisingly, the efficiency of conversion the antiherpetic 2'-deoxyguanosine analogues ACV, GCV, LBV, PCV, and A5021 to their phosphorylated forms by the A167Y mutant HSV-1 TK was far more pronounced than for the wild-type enzyme. Therefore, the single A167Y mutation converts the wild-type HSV-1 TK from a predominantly pyrimidine nucleos(t)ide kinase into a virtually exclusive purine (guanine) nucleoside analogue kinase.

First synthesis and anticancer activity of phosmidosine and its related compounds

This paper describes the first synthesis of phosmidosine and phosmidosine B, i.e., nucleotide antibiotics composed of 8-oxoadenosine and L-proline which are connected via a unique N-acyl phosphoramidate linkage. Phosmidosine has a yet-undetermined chiral center at the phosphorus atom of the N-acyl phosphoramidate linkage. Phosmidosine B is a demethylated phosmidosine derivative with no chirality on the phosphorus. Phosmidosine B was successfully synthesized by the reaction of an N-acetyl-8-oxoadenosine 5'-O-phosphoramidite derivative with an N-protected prolinamide in the presence of 5-(3,5-dinitrophenyl)-1H-tetrazole. The successful synthesis of phosmidosine was achieved by use of a tert-butoxycarbonyl (Boc) group, which was found to be selectively introduced into the 7-NH function of 8-oxoadenosine and to serve as a pseudo-protecting group due to its steric effect in such manner that the unmasked 6-amino group was not phosphitylated. Final coupling reaction of the 8-oxoadenosine 5'-phosphoramidite derivative with N-tritylprolinamide followed by full deprotection gave a mixture of phosmidosine and its diastereoisomer. The (13)C NMR spectra of the diastereomers suggest that the slow-eluted diastereomer 1b is the naturally occurring phosmidosine. The growth inhibitory activity of phosmidosine 1b, its diastereomer 1a, and phosmidosine B in various tumor cell lines was evaluated by the MTT assay. As the result, phosmidosine B showed high anticancer activities and both the diastereomers 1a and 1b of phosmidosine isolated were found to have similar but approximately 10 times higher anticancer activities than phosmidosine B. Moreover, it turned out that these phosmidosine derivatives showed characteristic inhibitory activities against cancer cells independent of their p53 phenotypes. These results suggest that phosmidosine and its related compounds would be promising as a new type of anticancer agents having a wide range of inhibitory activities against tumor cells.

The involvement of smooth muscle P2X receptors in the prolonged vasorelaxation response to purine nucleotides in the rat mesenteric arterial bed

1. ATP and adenine dinucleotides can elicit three different types of vasomotor response in the rat mesenteric arterial bed; vasocontraction, rapid relaxation (which may be masked by contraction) and slow and prolonged vasorelaxation. Contraction is mediated by smooth muscle P2X receptors and rapid relaxation by endothelial P2Y receptors. The mechanism of prolonged relaxation is, however, controversial. 2. In the present study, bolus injection of doses of alpha,beta-methylene ATP (alpha,beta-meATP; 5 pmol - 0.5 micromol; P2X receptor agonist) in methoxamine-preconstricted rat isolated mesenteric arterial beds, mimicked the action of ATP, causing contraction (R(max) 76+/-9 mmHg) followed by prolonged relaxation (78+/-11%; t(1/2) 14.6+/-1.5 min). KCl also elicited a biphasic response (R(max) contraction 73+/-8 mmHg; R(max) prolonged relaxation 70+/-6%; t(1/2) 7.7+/-1.9 min). 3. P2X receptor desensitization caused by perfusion with alpha,beta-meATP (10 microM) abolished contraction and prolonged relaxation to doses of alpha,beta-meATP (50 nmol). Rapid relaxation (32+/-7%; t(1/2) 32+/-2 s) was revealed, which was abolished by removal of the endothelium using distilled water. 4. Sodium deoxycholate treatment blocked contractile and prolonged relaxation responses to alpha,beta-meATP, ATP and KCl, whilst distilled water treatment had no significant effect on either phase of the biphasic responses. 5. These data indicate that smooth muscle P2X receptors are involved in both phases of the biphasic response (contraction followed by prolonged relaxation) to purine nucleotides in the rat isolated mesenteric arterial bed. Caution should be applied when using sodium deoxycholate to remove the endothelium because of possible damage caused by the detergent to receptors and/or the vascular smooth muscle.

ATP and other purine nucleotides stimulate the inactivation of ornithine transcarbamylase by broken lysosomes

Ornithine transcarbamylase (OTC) is very stable in rat liver homogenates, or mitochondria. However, pure OTC from rat or beef liver is inactivated by broken lysosomes. ATP and a number of purine nucleotides, particularly epsilon-ATP, stimulate the inactivation of OTC by broken lysosomes. Inactivation of OTC by trypsin and elastase is also stimulated by epsilon-ATP. Carbamoyl phosphate protects OTC against proteolytic attack by elastase or by broken lysosomes. Thus, environmental factors, e.g., ATP and carbamoyl phosphate, appear to influence OTC stability to proteases.

Regulation of rRNA transcription correlates with nucleoside triphosphate sensing

We have previously shown that the activity of the Escherichia coli rRNA promoter rrnB P1 in vitro depends on the concentration of the initiating nucleotide, ATP, and can respond to changes in ATP pools in vivo. We have proposed that this nucleoside triphosphate (NTP) sensing might contribute to regulation of rRNA transcription. To test this model, we have measured the ATP requirements for transcription from 11 different rrnB P1 core promoter mutants in vitro and compared them with the regulatory responses of the same promoters in vivo. The seven rrnB P1 variants that required much lower ATP concentrations than the wild-type promoter for efficient transcription in vitro were defective for response to growth rate changes in vivo (growth rate-dependent regulation). In contrast, the four variants requiring high ATP concentrations in vitro (like the wild-type promoter) were regulated with the growth rate in vivo. We also observed a correlation between NTP sensing in vitro and the response of the promoters in vivo to deletion of the fis gene (an example of homeostatic control), although this relationship was not as tight as for growth rate-dependent regulation. We conclude that the kinetic features responsible for the high ATP concentration dependence of the rrnB P1 promoter in vitro are responsible, at least in part, for the promoter's regulation in vivo, consistent with the model in which rrnB P1 promoter activity can be regulated by changes in NTP pools in vivo (or by hypothetical factors that work at the same kinetic steps that make the promoter sensitive to NTPs).

Feedback inhibition of amidophosphoribosyltransferase regulates the rate of cell growth via purine nucleotide, DNA, and protein syntheses

To clarify the contributions of amidophosphoribosyltransferase (ATase) and its feedback regulation to the rates of purine de novo synthesis, DNA synthesis, protein synthesis, and cell growth, mutated human ATase (mhATase) resistant to feedback inhibition by purine ribonucleotides was engineered by site-directed mutagenesis and expressed in CHO ade (-)A cells (an ATase-deficient cell line of Chinese hamster ovary fibroblasts) and in transgenic mice (mhATase-Tg mice). In Chinese hamster ovary transfectants with mhATase, the following parameters were examined: ATase activity and its subunit structure, the metabolic rates of de novo and salvage pathways, DNA and protein synthesis rates, and the rate of cell growth. In mhATase-Tg mice, ATase activity in the liver and spleen, the metabolic rate of the de novo pathway in the liver, serum uric acid concentration, urinary excretion of purine derivatives, and T lymphocyte proliferation by phytohemagglutinin were examined. We concluded the following. 1) ATase and its feedback inhibition regulate not only the rate of purine de novo synthesis but also DNA and protein synthesis rates and the rate of cell growth in cultured fibroblasts. 2) Suppression of the de novo pathway by the salvage pathway is mainly due to the feedback inhibition of ATase by purine ribonucleotides produced via the salvage pathway, whereas the suppression of the salvage pathway by the de novo pathway is due to consumption of 5-phosphoribosyl 1-pyrophosphate by the de novo pathway. 3) The feedback inhibition of ATase is more important for the regulation of the de novo pathway than that of 5-phosphoribosyl 1-pyrophosphate synthetase. 4) ATase superactivity leads to hyperuricemia and an increased bromodeoxyuridine incorporation in T lymphocytes stimulated by phytohemagglutinin.

Properties of native P2X receptors in rat trigeminal mesencephalic nucleus neurones: lack of correlation with known, heterologously expressed P2X receptors

Trigeminal mesencephalic nucleus (MNV) neurones express functional P2X receptors. In order to determine the molecular identity of the P2X receptors in this nucleus we have used whole cell patch clamp recording of P2X receptor-mediated currents to determine the pharmacological properties of the receptors, and have compared them with those of cloned P2X receptor subunits. The purine nucleotides ATP (300 microM), ATP-gamma-S (30 microM) and alphabetameATP (300 microM) evoked inward currents in all MNV neurones whereas alphabetameADP (300 microM) did not. betagammame-L-ATP (300 microM) evoked only a small ( approximately 20 pA) current in 3 out of 6 MNV neurones. The P2X receptor antagonist TNP-ATP (10 nM-10 microM) and raised extracellular Ca(2+) (8 and 30 mM) reduced, but did not abolish, the current evoked by ATP-gamma-S. The current remaining in TNP-ATP was insensitive to blockade by raised Ca(2+). These properties suggest that MNV neurones do not express homomeric P2X(3), P2X(4) or P2X(6) receptors. Whilst the TNP-ATP-insensitive ATP-gamma-S-evoked current has many characteristics similar to both homomeric P2X(2) and P2X(5) receptors, its insensitivity to blockade by raised Ca(2+) is difficult to reconcile with the receptor being a P2X(2) or P2X(5) homomeric channel. More likely, the receptor is a heteromer that comprises either or both of these subunits. The TNP-ATP-sensitive component of the ATP-gamma-S-evoked current is dissimilar to known cloned homomeric or heteromeric P2X receptors.

Structure-function relationships in UCP1, UCP2 and chimeras: EPR analysis and retinoic acid activation of UCP2

Uncoupling proteins (UCPs) are composed of three repeated domains of approximately 100 amino acids each. We have used chimeras of UCP1 and UCP2, and electron paramagnetic resonance (EPR), to investigate domain specific properties of these UCPs. Questions include: are the effects of nucleotide binding on proton transport solely mediated by amino acids in the third C-terminal domain, and are the amino acids in the first two domains involved in retinoic or fatty acid activation? We first confirmed that our reconstitution system produced UCP1 that exhibited known properties, such as activation by fatty acids and inhibition of proton transport by purine nucleotides. Our results confirm the observations reported for recombinant yeast that retinoic acid, but not fatty acids known to activate UCP1, activates proton transport by UCP2 and that this activation is insensitive to nucleotide inhibition. We constructed chimeras in which the last domains of UCP1 or UCP2 were switched and tested for activation by fatty acids or retinoic acid and inhibition by nucleotides. U1U2 is composed of mUCP1 (amino acids 1-198) and hUCP2 (amino acids 211-309). Fatty acids activated proton transport of U1U2 and GTP mediated inhibition. In the other chimeric construct U2U1, hUCP2 (amino acids 1-210) and mUCP1 (amino acids 199-307), retinoic acid still acted as an activator, but no inhibition was observed with GTP. Using EPR, a method well suited to the analysis of the structure of membrane proteins such as UCPs, we confirmed that UCP2 binds nucleotides. The EPR data show large structural changes in UCP1 and UCP2 on exposure to ATP, implying that a putative nucleotide-binding site is present on UCP2. EPR analysis also demonstrated changes in conformation of UCP1/UCP2 chimeras following exposure to purine nucleotides. These data demonstrate that a nucleotide-binding site is present in the C-terminal domain of UCP2. This domain was able to inhibit proton transport only when fused to the N-terminal part of UCP1 (chimera U1U2). Thus, residues involved in nucleotide inhibition of proton transport are located in the two first carrier motifs of UCP1. While these results are consistent with previously reported effects of the C-terminal domain on nucleotide binding, they also demonstrate that interactions with the N-terminal domains are necessary to inhibit proton transport. Finally, the results suggest that proteins such as UCP2 may transport protons even though they are not responsible for basal or cold-induced thermogenesis.

Purine and pyrimidine nucleotide-sensitive phospholipase A(2) in ampulla from frog semicircular canal

This study was attempted to characterize pharmacologically the P2Y receptors triggering phospholipase A(2) (PLA(2)) activation in ampulla from frog semicircular canal. A microassay was developed to screen the abilities of UTP analogs to stimulate [(3)H]arachidonic acid release by labeled ampullas. At 26 degrees C UTP induced a dose-dependent and saturable increase of PLA(2) activity (apparent activation constant 1.3 +/- 0.4 microM, Hill coefficient 0.9 +/- 0.2, maximal stimulating factor 2.0 +/- 0.1). The rank order of potency of agonists for PLA(2) activation was UTP > or = UDP > adenosine 5'-O-(2-thiodiphosphate) = adenosine 5'-O-(3-thiotriphosphate) > or = ATP = 2-methylthio-ATP > or = ADP = diadenosine tetraphosphate > or = alpha,beta-methylene-ATP = CTP > 2' and 3'-O-(4-benzoylbenzoyl)-ATP > or = AMP = UMP >> uridine and adenosine. UTP- and 2-methylthio-ATP-induced PLA(2) activations were inhibited by U-73122, GF-109203X, and methyl arachidonyl fluorophosphate. Basal activity was stimulated by phorbol ester and epinephrine and reduced by vasotocin, isoproterenol, prostaglandin E(2), cAMP, and forskolin. H-89 restored the cAMP- and forskolin-inhibited PLA(2) activities. Results indicate that P2Y receptor-mediated PLA(2) stimulation requires phopholipase C and protein kinase C activations and basal activity is inhibited by agonist-stimulated cAMP-dependent mechanisms.

Selective regulatory effects of purine and pyrimidine nucleotides on vacuolar transport of amino acids

The release of amino acids from their vacuolar store was studied in situ, i.e. in cells with selectively permeabilized plasma membrane and functionally intact vacuoles. As we previously described [Roos et al., J. Biol. Chem. 272 (1997) 15849-15855], this transport process is regulated by extravacuolar adenylates at their physiological concentrations. We now show, using our test object Penicillium cyclopium, that not only purine but also pyrimidine nucleotides are involved in the control of efflux of vacuolar phenylalanine. At 0.1 mM adenosine or guanosine phosphates inhibit, whereas cytidine or uridine phosphates stimulate the rate of efflux. At 1 mM the same nucleotides have no measurable impact on efflux but abolish the effects of other nucleotides present at 0.1 mM. This argues for at least two interacting binding sites with different nucleotide affinities. The minimum structural requirement for any of the observed effects is a non-cyclic ribonucleoside monophosphate. In intact cells, cytosolic concentrations of ATP (representing purine nucleotides) and CTP (representing pyrimidine nucleotides) are 1-2 mM and 0.05-0.2 mM, respectively. ATP is therefore assumed to dominate transport control and allow optimum efflux (and uptake) rates. Short-time starvation of carbon and nitrogen adjusts CTP and ATP at levels that cause declining efflux rates. During prolonged starvation both nucleotides fall below their transport-controlling concentrations and thus allow increasing rates of efflux from the still maintained vacuolar pool. Hence, efflux control under nutrient limitation includes an interplay of purine and pyrimidine nucleotides which precisely regulates the release of vacuolar amino acids and enables flexible adjustment to either amino acid saving or cell survival.

Regulation of the activity of 27 pS nonselective cation channels in excised membrane patches from rat brown-fat cells

The regulation of the activity of the approximately 30 pS nonselective cation channel (NSC channel) was studied by the patch-clamp technique in inside-out patches obtained from rat brown-fat cells. NSC channel activity was induced by excision; reduced redox state induced by dithiothreitol accelerated the kinetics in the excised state. The NSC channels were inhibited by the fenamates flufenamic acid and mefenamic acid but not by NS-1619 or SKF-96365. The channels were inhibited by purine nucleotides but not by polyamines. No evidence for protein kinase C, CaM kinase or protein kinase A activation of the NSC channel was obtained. NSC-channel activity was stimulated in a concentration-dependent manner by Ca2+ but the EC50 was very high (0.81 mM), in comparison to expected cytosolic Ca2+ levels. In the presence of ATP, even higher Ca2+ levels were necessary for comparable NSC-channel activation. The increase in Po was not associated with an increase in open-time constants. We conclude that although high Ca2+ levels can experimentally activate the NSC channel, a further mediatory step must probably be postulated in order to link alpha1-adrenergic stimulation to NSC-channel activation.

Uncoupling proteins 1 and 3 are regulated differently

Using a heterologous yeast expression system, we have previously found a marked discordance between the effects of uncoupling protein (UCP) 1 and UCP3L on basal O(2) consumption in whole yeast versus isolated mitochondria. In whole yeast, UCP3L produces a greater stimulation of basal O(2) consumption, while in isolated mitochondria, UCP1 produces a much greater effect. As shown previously and in this report, UCP3L, in contrast to UCP1, is not inhibited by purine nucleotides. In the present study, we addressed two hypothetical mechanisms that could account for the observed discordance: (i) in whole yeast, purine nucleotides inhibit UCP1 but not UCP3L and (ii) preparations of isolated mitochondria lack an activator of UCP3L that is normally present in vivo. By use of a mutant of UCP1 that lacks purine nucleotide inhibition, it is demonstrated that cytosolic concentrations of purine nucleotides present in yeast effectively inhibit UCP1 activity. This suggests that the lower activity of UCP1 compared to UCP3L in whole yeast is due to purine nucleotide inhibition of UCP1 but not UCP3L. As potential activators of UCP3L we tested free fatty acids in whole yeast and isolated mitochondria. While UCP1 was strongly activated by free fatty acids, no stimulatory effect on UCP3L was observed. In summary, this study indicates that UCP1 and UCP3L differ in their regulation by purine nucleotides and free fatty acids. This different regulation may be related to different physiological functions of the two proteins.

[Efficacy of purine nucleotides on purinergic P2 platelet receptors by small angle light scattering]

The effect of purines on the activation and aggregation of thrombocytes in rats and rabbits was studied by the method of small-angle light scattering. The EC50 values of ADP, inducing the activation and aggregation of thrombocytes, reflect the sequence of the agonist action on various receptors: P2X1, 20-40 nM; P2Y1, 90-110 nM; P2YADP, 120-240 nM. It was demonstrated that ADP behaves as partial agonist not only with respect to P2X1 receptors, but with respect to P2Y1 receptors as well. Thrombocytes activated by 20 nM ADP or 100-nM ATP pass into a refracter state in the absence of further stimulation. The reaction halftime is tau 1/2 = 6.0 +/- 0.2 min for the cells activated with ADP and tau 1/2 = 16.5 +/- 0.2 min for ADP.

Transport function and regulation of mitochondrial uncoupling proteins 2 and 3

Uncoupling protein 1 (UCP1) dissipates energy and generates heat by catalyzing back-flux of protons into the mitochondrial matrix, probably by a fatty acid cycling mechanism. If the newly discovered UCP2 and UCP3 function similarly, they will enhance peripheral energy expenditure and are potential molecular targets for the treatment of obesity. We expressed UCP2 and UCP3 in Escherichia coli and reconstituted the detergent-extracted proteins into liposomes. Ion flux studies show that purified UCP2 and UCP3 behave identically to UCP1. They catalyze electrophoretic flux of protons and alkylsulfonates, and proton flux exhibits an obligatory requirement for fatty acids. Proton flux is inhibited by purine nucleotides but with much lower affinity than observed with UCP1. These findings are consistent with the hypothesis that UCP2 and UCP3 behave as uncoupling proteins in the cell.

Identification and characterization of a protozoan uncoupling protein in Acanthamoeba castellanii

An uncoupling protein (UCP) has been identified in mitochondria from Acanthamoeba castellanii, a nonphotosynthetic soil amoeboid protozoon that, in molecular phylogenesis, appears on a branch basal to the divergence points of plants, animals, and fungi. The existence of UCP in A. castellanii (AcUCP) has been revealed using antibodies raised against plant UCP. Its molecular mass (32,000 Da) was similar to those of plant and mammalian UCPs. The activity of AcUCP has been investigated in mitochondria depleted of free fatty acids. Additions of linoleic acid stimulated state 4 respiration and decreased transmembrane electrical potential (DeltaPsi) in a manner expected from fatty acid cycling-linked H(+) reuptake. The half-maximal stimulation by linoleic acid was reached at 8.1 +/- 0.4 microM. Bovine serum albumin (fatty acid-free), which adsorbs linoleic acid, reversed the respiratory stimulation and correspondingly restored DeltaPsi. AcUCP was only weakly inhibited by purine nucleotides like UCP in plants. A single force-flow relationship has been observed for state 4 respiration with increasing concentration of linoleic acid or of an uncoupler and for state 3 respiration with increasing concentration of oligomycin, indicating that linoleic acid has a pure protonophoric effect. The activity of AcUCP in state 3 has been evidenced by ADP/oxygen atom determination. The discovery of AcUCP indicates that UCPs emerged, as specialized proteins for H(+) cycling, early during phylogenesis before the major radiation of phenotypic diversity in eukaryotes and could occur in the whole eukaryotic world.

Effects of guanine, inosine, and xanthine nucleotides on beta(2)-adrenergic receptor/G(s) interactions: evidence for multiple receptor conformations

The aim of our study was to examine the effects of different purine nucleotides [GTP, ITP, and xanthosine 5'-triphosphate (XTP)] on receptor/G protein coupling. As a model system, we used a fusion protein of the beta(2)-adrenergic receptor and the alpha subunit of the G protein G(s). GTP was more potent and efficient than ITP and XTP at inhibiting ternary complex formation and supporting adenylyl cyclase (AC) activation. We also studied the effects of several beta(2)-adrenergic receptor ligands on nucleotide hydrolysis and on AC activity in the presence of GTP, ITP, and XTP. The efficacy of agonists at promoting GTP hydrolysis correlated well with the efficacy of agonists for stimulating AC in the presence of GTP. This was, however, not the case for ITP hydrolysis and AC activity in the presence of ITP. The efficacy of ligands at stimulating AC in the presence of XTP differed considerably from the efficacies of ligands in the presence of GTP and ITP, and there was no evidence for receptor-regulated XTP hydrolysis. Our findings support the concept of multiple ligand-specific receptor conformations and demonstrate the usefulness of purine nucleotides as tools to study conformational states of receptors.

Structure-antiviral activity relationship in the series of pyrimidine and purine N-[2-(2-phosphonomethoxy)ethyl] nucleotide analogues. 1. Derivatives substituted at the carbon atoms of the base

A series of dialkyl esters of purine and pyrimidine N-[2-(phosphonomethoxy)ethyl] derivatives substituted at position 2, 6, or 8 of the purine base or position 2, 4, or 5 of the pyrimidine base were prepared by alkylation of the appropriate heterocyclic base with 2-chloroethoxymethylphosphonate diester in the presence of sodium hydride, cesium carbonate, or 1,8-diazabicyclo[5,4, 0]undec-7-ene (DBU) in dimethylformamide. Additional derivatives were obtained by the transformations of the bases in the suitably modified intermediates bearing reactive functions at the base moiety. The diesters were converted to the corresponding monoesters by sodium azide treatment, while the free acids were obtained from the diester by successive treatment with bromotrimethylsilane and hydrolysis. None of the PME derivatives in the pyrimidine series, their 6-aza or 3-deaza analogues, exhibited any activity against DNA viruses or retroviruses tested, except for the 5-bromocytosine derivative. Substitution of the adenine ring in PMEA at position 2 by Cl, F, or OH group decreased the activity against all DNA viruses tested. PMEDAP was highly active against HSV-1, HSV-2, and VZV in the concentration range (EC50) of 0.07-2 microg/mL. Also the 2-amino-6-chloropurine derivative was strongly active (EC50 = 0.1-0. 4 microg/mL) against herpes simplex viruses and (EC50 = 0.006-0.3 microg/mL) against CMV and VZV. PMEG was the most active compound of the whole series against DNA viruses (EC50 approximately 0.01-0.02 microg/mL), though it exhibited significant toxicity against the host cells. The base-modified compounds did not show any appreciable activity against DNA viruses except for 7-deazaPMEA (IC50 approximately 7.5 microg/mL) against HIV-1 and MSV. The neutral (diisopropyl, diisooctyl) diesters of PMEA were active against CMV and VZV, while the corresponding monoesters were inactive. The diisopropyl ester of the 2-chloroadenine analogue of PMEA showed substantially (10-100x) higher activity against CMV and VZV than the parent phosphonate. Also, the diisopropyl and diisooctyl ester of PMEDAP inhibited CMV and VZV, but esterification of the phosphonate residue did not improve the activity against either MSV or HIV.

Purine metabolites suppress proliferation of human NK cells through a lineage-specific purine receptor

NK cell proliferation is suppressed in some patients with cancer by unknown mechanisms. Because purine metabolites released into the extracellular space during cell lysis may affect cell function, we hypothesized that these metabolites could serve as feedback regulators of NK cell proliferation. Sorted NK (CD56+/CD3-) cells were incubated with IL-2 (1000 U/ml) in a 4-day thymidine uptake assay with or without 10-10,000 microM of nucleotides. Adenine nucleotides inhibited NK cell proliferation, with ATP = ADP > 5'-adenylylimidodiphosphate > AMP = adenosine; ADP-ribose and nicotinamide adenine dinucleotide, but not nicotinamide or UTP, caused a dose-dependent suppression of thymidine uptake. A total of 100 microM ATP, a concentration that induced a maximal (80%) inhibition of thymidine uptake, did not inhibit cytotoxic activity against K562 targets. Because NK cells retained the ability to lyse K562 targets 4 days after exposure to 500 microM ATP or 1000 microM adenosine, inhibition of thymidine uptake was not due to cell death. Incubation of NK cells with dibutyryl cAMP and forskolin also suppressed thymidine uptake. Cholera toxin and pertussis toxin suppressed NK cell proliferation. Pertussis toxin did not block the adenine nucleotide effects. Further, ATP, but not adenosine or other nucleotides, markedly increased intracellular cAMP in a dose-dependent manner. The ATP-induced increase in cAMP was specific to cytolytic cells, because CD19+ B cells and CD4+ T cells did not increase their intracellular cAMP. These studies demonstrate that NK proliferation is regulated through purine receptors by adenine nucleotides, which may play a role in decreased NK cell activity. The response to adenine nucleotides is lineage-specific.

Purine and pyrimidine nucleotides inhibit a noninactivating K+ current and depolarize adrenal cortical cells through a G protein-coupled receptor

Bovine adrenal zona fasciculata (AZF) cells express a noninactivating K+ current (IAC) that sets the resting membrane potential and may mediate depolarization-dependent cortisol secretion. External ATP stimulates cortisol secretion through activation of a nucleotide receptor. In whole-cell patch clamp recordings from bovine AZF cells, we found that ATP selectively inhibited IAC K+ current by a maximum of 75.7 +/- 3% (n = 13) with a 50% inhibitory concentration of 1.3 microM. A rapidly inactivating A-type K+ current was not inhibited by ATP. Other nucleotides, including ADP and the pyrimidines UTP and UDP, also inhibited IAC, whereas 2-methylthio-ATP (2-MeSATP) and CTP were completely ineffective. The rank order of potency for six nucleotides was UTP = ADP > ATP > UDP >> 2-MeSATP = CTP. At maximally effective concentrations, UTP, ADP, and UDP inhibited IAC current by 81.4 +/- 5.2% (n = 7), 70.7 +/- 7.2% (n = 4), and 65.2 +/- 7.9% (n = 5), respectively. Inhibition of IAC by external ATP was reduced from 71. 3 +/- 3.2% to 22.8 +/- 4.5% (n = 18) by substituting guanosine 5'-O-2-(thio) diphosphate for GTP in the patch pipette. Inhibition of IAC by external ATP (10 microM) was markedly suppressed (to 17.3 +/- 5.5%, n = 9) by the nonspecific protein kinase antagonist staurosporine (1 microM) and eliminated by substituting the nonhydrolyzable ATP analog 5-adenylyl-imidodiphosphate or UTP for ATP in the pipette. ATP-mediated inhibition of IAC was not altered by the kinase C antagonist calphostin C, the calmodulin inhibitory peptide, or by buffering the intracellular (pipette) Ca++ with 20 mM 1,2-bis-(2-aminophenoxy)ethane-N, N,N',N'-tetraacetic acid. In current clamp recordings, ATP and UTP (but not CTP) depolarized AZF cells at concentrations that inhibited IAC K+ current. These results demonstrate that bovine AZF cells express a nucleotide receptor with a P2Y3 agonist profile that is coupled to the inhibition of IAC K+ channels through a GTP-binding protein. The inhibition of IAC K+ current and associated membrane depolarization are the first cellular responses demonstrated to be mediated through this receptor. Nucleotide inhibition of IAC proceeds through a pathway that is independent of phospholipase C, but that requires ATP hydrolysis. The identification of a new signaling pathway in AZF cells, whereby activation of a nucleotide receptor is coupled to membrane depolarization through inhibition of a specific K+ channel, suggests a mechanism for ATP-stimulated corticosteroid secretion that depends on depolarization-dependent Ca++ entry. This may be a means of synchronizing the stress-induced secretion of corticosteroids and catecholamines from the adrenal gland.

Purine nucleotide- and sugar phosphate-induced inhibition of the carboxyl methylation and catalysis of protein phosphatase-2A in insulin-secreting cells: protection by divalent cations

Recently, we demonstrated that the 36 kDa catalytic subunit of protein phosphatase 2A (PP2Ac) undergoes methylation at its C-terminal leucine in normal rat islets, human islets and isolated beta cells; this modification increases the catalytic activity of PP2A [Kowluru et al. Endocrinology. 137:2315-2323, 1996]. Previous studies have suggested that adenine and guanine nucleotides or glycolytic intermediates [which are critical mediators in beta cell function] also modulate phosphatase activity in the pancreatic beta cell. Therefore, we examined whether these phosphorylated molecules specifically regulate the carboxyl methylation and the catalytic activity of PP2A in beta cells. Micromolar concentrations of ATP, ADP, GTP or GDP each inhibited the carboxyl methylation of PP2Ac and, to a lesser degree, the catalytic activity of PP2A. Likewise, the carboxyl methylation of PP2Ac and its catalytic activity were inhibited by [mono- or di-] phosphates of glucose or fructose. Additionally, however, the carboxyl methylation of PP2Ac was significantly stimulated by divalent metal ions (Mn2+ > Mg2+ > Ca2+ > control). The nucleotide or sugar phosphate-mediated inhibition of carboxyl methylation of PP2Ac and the catalytic activity of PP2A were completely prevented by Mn2+ or Mg2+. These data indicate that divalent metal ions protect against the inhibition by purine nucleotides or sugar phosphates of the carboxyl methylation of PP2Ac perhaps permitting PP2A to function under physiologic conditions. Therefore, these data warrant caution in interpretation of extant data on the regulation of phosphatase function by purine nucleotides.

Neurochemical and morphological responses to acutely and chronically implanted brain microdialysis probes

The purpose of this study was to compare, in rats, brain microdialysis results obtained using microdialysis probes implanted acutely for 2 h versus probes implanted chronically for 24 h in the caudate. Specific comparisons included: (1) dialysate purine and amino acid profiles during cerebral ischemia; (2) diffusional characteristics of the microdialysis probe; and (3) tissue morphology surrounding the probe. During ischemia, the increase in dialysate levels of adenosine, inosine, and hypoxanthine was less pronounced from probes implanted chronically, while dialysate xanthine levels increased to a greater extent. An increase in dialysate amino acid neurotransmitters during cerebral ischemia was observed in the acutely implanted probes within 10 min of the onset of cerebral ischemia; in the chronically implanted probes this increase did not occur until after 50 min of severe ischemia. Both in vitro and in vivo tests revealed a diffusional barrier in chronically implanted probes. Moreover, the tissue surrounding chronically implanted probes exhibited a high degree of inflammation, and fibrin deposits were substantial. In addition, uric acid levels (an indicator of tissue injury) sampled from chronically implanted probes were 7-fold greater than levels sampled from acutely implanted probes. These data raise concerns about the use of chronically implanted microdialysis probes for the measurement of purine and amino acid profiles during cerebral ischemia.

Inhibition of cyclin D1 expression and phosphorylation of retinoblastoma protein by phosmidosine, a nucleotide antibiotic

In this report, we studied the effect of phosmidosine, a proline-containing nucleotide on the serum-induced cell cycle progression in human lung fibroblast WI-38 cells. Phosmidosine suppressed S-phase entry and arrested cell cycle progression at the G1 phase. In serum-stimulated cells, phosmidosine did not affect the activation of the mitogen-activated protein kinase cascade. However, phosmidosine inhibited hyperphosphorylation of retinoblastoma (RB) protein by RB-kinases such as cyclin-dependent kinase 4 and cyclin-dependent kinase 2, probably as a result of the inhibition of cyclin D1 expression. Furthermore, in tsFT210 cells, a temperature-sensitive cdc2 mutant isolated from the mouse mammary carcinoma cell line FM3A, phosmidosine, irreversibly inhibited the cell cycle progression at G1 without affecting the G2 to M transition. Phosmidosine acts at an earlier point in G1 compared with mimosine or aphidicolin, well-known cell cycle blockers at the G1-S boundary. Taken together, phosmidosine arrested cells at a specific point between the start point and restriction point in G1 and is a useful drug that may contribute to the understanding of the regulatory mechanisms of G1 progression.

Nucleoside transport mechanisms in the pigmented rabbit conjunctiva

PURPOSE

To elucidate the mechanisms of nucleoside transport in the pigmented rabbit conjunctiva using [3H]uridine as the substrate.

METHODS

Excised pigmented rabbit conjunctiva was mounted in a modified Ussing chamber for measurement of short-circuit current (Isc) and [3H]uridine transport.

RESULTS

[3H]Uridine transport in the mucosal-to-serosal direction at 10 microM exhibited directionality, temperature dependency, and phlorizin sensitivity. Uridine transport appeared to be mediated via saturable Na(+)-dependent and nitrobenzylthioinosine-insensitive Na(+)-independent processes. The corresponding Michaelis-Menten constants (K(m)) were 1.9 microM and 200 microM, and the maximal uridine fluxes (Jmax) were 29.3 and 46.7 pmol/cm2 per minute. When added to the mucosal side containing 141 mM Na+, uridine increased the Isc in a dose-dependent manner from 0.005 mM to 1.0 mM at 37 degrees C. The K(m) value was 7.6 microM, and the maximal increase in Isc was 0.71 microA/cm2. Hill analysis of uridine transport at 10 microM in the presence of varying Na+ concentrations in the mucosal bathing fluid yielded a Hill coefficient of 1.1, suggesting a 1:1 coupling between Na+ and uridine. Na(+)-dependent uridine transport was inhibited by 10 microM adenosine, guanosine, and inosine, but not by thymidine, suggesting that the transport process may be mainly selective for purine nucleosides. Moreover, 2'-deoxyuridine, 5-iodo-2'-deoxyuridine, and 5-(2-bromovinyl)-2'-deoxyuridine were potent inhibitors of Na(+)-dependent uridine transport.

CONCLUSIONS

Na(+)-dependent and Na(+)-independent nucleoside transport processes appeared to be localized on the mucosal aspect of the pigmented rabbit conjunctiva. One or more Na(+)-coupled uridine cotransport processes exhibited a 1:1 stoichiometry and an apparent preference toward purine nucleosides.

Mechanism of the synergistic end-product regulation of Bacillus subtilis glutamine phosphoribosylpyrophosphate amidotransferase by nucleotides

De novo purine nucleotide synthesis is regulated, at least in part, by end-product inhibition of glutamine PRPP amidotransferase. An important feature of this inhibition is the fact that certain synergistic nucleotide pairs give more than additive inhibition. The physiological importance of synergism is in amplifying regulation by the adenine and guanine nucleotide end products of de novo synthesis. Using a new method to quantitate synergism, ADP plus GMP were confirmed [Meyer, E., and Switzer, R. L. (1978) J. Biol. Chem. 254, 5397-5402] to give strong synergistic inhibition of Bacillus subtilis glutamine PRPP amidotransferase. An X-ray structure of the ternary enzyme.ADP.GMP complex established that ADP binds to the allosteric A site and GMP to the catalytic C site. GMP increased the binding affinity of ADP for the A site by approximately 20-fold. Synergism results from a specific nucleotide-nucleotide interaction that is dependent upon a nucleoside diphosphate in the A site and a nucleoside monophosphate in the C site. Furthermore, synergism is enhanced by the competition between nucleotide inhibitor and PRPP substrate for the C site. Purine base specificity results from a backbone carbonyl interaction of Lys305' with the 6-NH2 group of adenine in the A site and a Ser347 Ogamma interaction with the 2-NH2 group of guanine in the C site. Steric considerations favor binding of the nucleoside diphosphate to the A site. Site-directed replacements of key residues increased the nucleotide concentrations needed for 50% inhibition and in some cases perturbed synergism. Mutations in either of the nucleotide sites perturbed function at both sites, supporting the important role of synergism.

[Development of new antitumor reagents which block the cell cycle progression]

Most tumor cells have abnormalities in the cell-cycle regulation system. Cyclin-dependent kinases (cdk) are major regulatory molecules for the cell cycle control. Therefore, cell cycle inhibitors, especially cdk-inhibitors, may be a promising new type of antitumor drug. In this review, low-molecular-weight cell-cycle inhibitors isolated from mainly microorganisms are described. As the activation of cdk is caused by the association with cyclins as well as by their phosphorylation and dephosphorylation, kinase inhibitors and phosphatase inhibitors are also candidates for cell cycle inhibitors.

Characterization of P2 receptors for purine and pyrimidine nucleotides in human placental cotyledons

1. The aim of this study was to characterize P2 receptors in the arterial vascular bed of human perfused placental cotyledons. Vasoconstrictor responses to bolus injections of purine and pyrimidine nucleotides were tested at basal tone, and vasodilator responses in preparations with tone raised by perfusion with prostaglandin F2alpha (PGF2alpha; 10-50 nM). 2. At basal tone, bolus injections of the P2X-selective agonist alpha,beta-methylene ATP (alpha,beta-meATP; 0.5-500 nmol) elicited dose-dependent vasoconstriction. ATP (0.005-5 micromol) also elicited dose-dependent vasoconstriction, but was less potent than alpha,beta-meATP. Vasoconstriction was also elicited by other nucleotides, but only at the highest dose tested (5 micromol): UTP > CTP = ITP (n = 6). GTP and TTP did not cause vasoconstriction. 3. Constrictor responses to bolus injections of alpha,beta-meATP were resistant to desensitization and were not significantly affected when carried out in the presence of 1 microM alpha,beta-meATP added to the perfusate. However, responses to bolus injections of alpha,beta-meATP were partially blocked by perfusion with 10 microM alpha,beta-meATP. In contrast, responses to ATP and UTP were unaffected by 10 microM alpha,beta-meATP. The P2X receptor antagonist pyridoxalphosphate-6-azophenyl-2',4'-disulphonic acid (PPADS; 10 and 100 microM) had no significant effect on vasoconstriction mediated by alpha,beta-meATP and ATP. 4. Removal of the endothelium had no significant effect on constrictor responses to alpha,beta-meATP, ATP and UTP. Inhibition of nitric oxide (NO) synthesis with N(G)-nitro-L-arginine methyl ester (L-NAME; 100 microM) had no significant effect on vasoconstriction to ATP and alpha,beta-meATP. 5. In preparations with tone raised with PGF2alpha (10-50 nM) vasodilatation was elicited by nucleotides with the following order of potency: 2MeSATP = ADP >> ATP > UTP > CTP = GTP = ITP = TTP. pD2 values were: 2MeSATP, 10.03+/-0.26 (n=7); ADP, 9.97+/-0.40 (n=5); ATP, 8.89+/-0.18 (n=7); UTP, 7.79+/-0.35 (n=7). Maximal responses to 2MeSATP and ADP were similar and were approximately 40% greater than maximal responses to ATP and UTP. 6. Vasodilator responses to nucleotides were abolished by L-NAME (100 microM) and by removal of the endothelium. 7. In conclusion, contractile responses mediated by alpha,beta-meATP and ATP in human placental smooth muscle are resistant to desensitization and insensitive to PPADS and, thus, show a dissimilar pharmacological profile to the classic smooth muscle P2X1 receptor. There may be two subtypes of smooth muscle P2 receptor based on differential antagonism of alpha,beta-meATP and ATP with alpha,beta-meATP. A smooth muscle P2 receptor mediates vasoconstriction to UTP, and may indicate a further subtype. Endothelium-dependent, NO-dependent, vasodilatation to 2MeSATP and ADP may be mediated by P2Y1 receptors, while endothelial P2Y2 receptors are likely to mediate NO-dependent relaxation to ATP and UTP.

Roles of purine nucleotides and adenosine in enhancing NOS II gene expression in interleukin-1 beta-stimulated rat vascular smooth muscle cells

The production of nitric oxide (NO) by vascular smooth muscle cells (VSMC) is stimulated by interleukin-1 beta (IL-1 beta). This is enhanced in a dose-dependent manner by ADP, although it alone failed to induce nitrite accumulation. Purine nucleotides and their nonhydrolizable analogues as well as adenosine also exhibit variable enhancing effects. This enhanced nitrite formation was due to induction of the NO synthase (NOS II) gene as judged by Northern hybridization using an NOS II specific probe and by Ca2+ independency of the NOS II activity. 8-(p-Sulfophenyl)-theophylline, a blocker of adenosine receptors, suppressed the enhanced NO production by adenosine and ADP to the level of that with IL-1 beta alone. These data indicate that activation of the adenosine receptor on VSMC may enhance production of NOS II by modulating a signal transducing pathway of IL-1 beta. Although cAMP is a candidate as the second messenger, it was not significantly elevated by either ADP or adenosine treatment in IL-1 beta-stimulated cells. This mechanism might be stimulated under conditions with release of various purine and their derivatives.

Effects of purine nucleotides and nucleoside on cytosolic calcium levels in rat tracheal smooth muscle cells

Extracellular adenosine triphosphate (ATP) has a range of effects on a wide variety of cells through the activation of specific purinoceptors. The aim of this study was to establish whether P2 purinoceptors are present on airway smooth muscle cells. Experiments were conducted on cultured rat tracheal smooth-muscle cells (first through third passage). Intracellular Ca2+ ([Ca2+]i) was measured using Fura-2 and dual-excitation wavelength microfluorometry. The effects of ATP, adenosine diphosphate (ADP), uridine triphosphate (UTP), and adenosine (ADO) were measured in concentrations from 10(-6) to 10(-3) M. At a concentration of 10(-4) M, the peak [Ca2+]i was 502 +/- 92 nM for ATP and 543 +/- 76 nM for UTP (mean +/- standard error of the mean). ADO had no significant effect on Ca2+ release. Peak [Ca2+]i induced by ATP was not dependent on extracellular Ca2+ but was blocked by U-73122, an inhibitor of phospholipase C. Pretreatment with adenosine deaminase and desensitization with alphabeta-MeATP had no effect on ATP-induced Ca2+ release. The effects of ATP (10(-4) M) on peak [Ca2+]i were potentiated by the presence of ADO 10(-5) M (969 +/- 257 nM; P < 0.05). The presence of XAC, a blocker of A1 and A2 ADO receptors did not prevent this effect. In the presence of XAC, ADO 10(-6) M potentiated the effects of ATP (peak [Ca2+]i: 1,300 +/- 229 nM). The addition of 1433U83, a blocker of A3 ADO receptors, blocked the synergistic effect of ADO 10(-6) M on ATP. These data show that P2 purinoceptors, most likely of the P2U subtype, are present on airway smooth muscle cells and that the newly discovered A3 ADO receptor appears to be also present.

Purine and pyrimidine nucleotide-sensitive phosphoinositidase C in ampulla from frog semicircular canal

A microassay was developed to screen the abilities of ATP analogues to stimulate phosphoinositidase C in single ventral regions (including dark cells and sensory cells) of ampullas microdissected from posterior vertical semicircular canals of Rana ridibundo and labeled with myo-[3H]inositol. ATP induced a dose-dependent and saturable increase of total [3H]linositol phosphate production accompanied by an equivalent decrease in the [3H]phosphoinositide pool. The rank order of analogues revealing agonistic potencies for phosphoinositidase C activation was as follows: uridine 5'-triphosphate > or = adenosine 5'-O-[3-thiophosphate] tetralithium > adenosine 5'-O-[2-thiodiphosphate] trilithium > or = ATP > or = ADP = inosine 5'-triphosphate > or = guanosine 5'-triphosphate > or = 2-methylthio-adenosine 5'-triphosphate tetrasodium > or = 2'-desoxy-thymidine 5'-triphosphate > or = cytidine 5'-triphosphate = (alpha, beta)-methyl ATP > AMP, whereas adenosine 3',5'-cyclic monophosphate and adenosine were almost devoid of activity. For antagonists, 1,4'-diisothiocyanostilbene-2, 2'-disulfonic acid was far more active than suramin for competitive inhibition of ATP-induced enzyme stimulation, whereas reactive blue 2 acted as a noncompetitive inhibitor. Results indicate that the putative P2 receptors triggering phosphoinositidase C activation in ventral ampullary epithelium from frog semicircular canal exhibit mainly the functional properties of P2Y and P2U receptors.