ATP stimulates sympathetic transmitter release via presynaptic P2X purinoceptors

ATP is a fast transmitter in sympathetic ganglia and at the sympathoeffector junction. In primary cultures of dissociated rat superior cervical ganglion neurons, ATP elicits noradrenaline release in an entirely Ca2+-dependent manner. Nevertheless, ATP-evoked noradrenaline release was only partially reduced (by approximately 50%) when either Na+ or Ca2+ channels were blocked, which indicates that ATP receptors themselves mediated transmembrane Ca2+ entry. An "axonal" preparation was obtained by removing ganglia from explant cultures, which left a network of neurites behind; immunostaining for axonal and dendritic markers revealed that all of these neurites were axons. In this preparation, ATP raised intraaxonal Ca2+ and triggered noradrenaline release, and these actions were not altered when Ca2+ channels were blocked by Cd2+. Hence, Ca2+-permeable ATP-gated ion channels, i.e., P2X purinoceptors, are located at presynaptic sites and directly mediate Ca2+-dependent transmitter release. These presynaptic P2X receptors displayed a rank order of agonist potency of ATP >/= 2-methylthio-ATP > ATPgammaS > alpha,beta-methylene-ATP approximately beta,gamma-methylene-L-ATP and were blocked by suramin or PPADS. ATP, 2-methylthio-ATP, and ATPgammaS also evoked inward currents measured at neuronal somata, but there these agonists were equipotent. Hence, presynaptic P2X receptors resemble the cloned P2X2 subtype, but they appear to differ from somatodendritic P2X receptors in terms of agonist sensitivity. Suramin reduced depolarization-evoked noradrenaline release by up to 20%, when autoinhibitory mechanisms were inactivated by pertussis toxin. These results indicate that presynaptic P2X purinoceptors mediate a positive, whereas G-protein-coupled P2Y purinoceptors mediate a negative, feedback modulation of sympathetic transmitter release.     

Adenosine: a mediator of the sleep-inducing effects of prolonged wakefulness

Both subjective and electroencephalographic arousal diminish as a function of the duration of prior wakefulness. Data reported here suggest that the major criteria for a neural sleep factor mediating the somnogenic effects of prolonged wakefulness are satisfied by adenosine, a neuromodulator whose extracellular concentration increases with brain metabolism and which, in vitro, inhibits basal forebrain cholinergic neurons. In vivo microdialysis measurements in freely behaving cats showed that adenosine extracellular concentrations in the basal forebrain cholinergic region increased during spontaneous wakefulness as contrasted with slow wave sleep; exhibited progressive increases during sustained, prolonged wakefulness; and declined slowly during recovery sleep. Furthermore, the sleep-wakefulness profile occurring after prolonged wakefulness was mimicked by increased extracellular adenosine induced by microdialysis perfusion of an adenosine transport inhibitor in the cholinergic basal forebrain but not by perfusion in a control noncholinergic region.     

Selectivity and activity of adenine dinucleotides at recombinant P2X2 and P2Y1 purinoceptors

1. Adenine dinucleotides (Ap3A, x = 2-6) are naturally-occurring polyphosphated nucleotidic substances which are found in the CNS and are known to be released in a calcium-dependent manner from storage vesicles in brain synaptosomes. The selectivity and activity of adenine dinucleotides for neuronally-derived recombinant P2 purinoceptors were studied using P2X2 and P2Y1 subtypes expressed in Xenopus oocytes. 2. For the P2Y1 subtype derived from chick brain, Ap3A was equipotent and as active as ATP (EC50 values: 375 +/- 86 nM and 334 +/- 25 nM, respectively). Ap4A was a weak partial agonist and other dinucleotides were inactive as agonists. None of the inactive dinucleotides were antagonists nor modulated the activity of Ap3A and ATP. 3. For the P2X2 subtype derived from rat PC12 cells, Ap4A was as active as ATP but less potent (EC50 values: 15.2 +/- 1 microM and 3.7 +/- 0.7 microM, respectively). Other adenosine dinucleotides were inactive as either agonists or antagonists. 4. Ap5A (1-100 nM) potentiated ATP-responses at the P2X2 subtype, showing an EC50 of 2.95 +/- 0.7 nM for this modulatory effect. Ap5A (10 nM) shifted the concentration-response curves for ATP to the left by one-half log10 unit but did not alter the Hill co-efficient for ATP (nH = 2.1 +/- 0.1). Ap5A (10 nM) failed to potentiate Ap4A-responses but did enhance the efficacy of the P2 purinoceptor antagonist, suramin, by 12 fold at the P2X2 subtype. 5. In conclusion, the results show that ionotropic (P2X2) and metabotropic (P2Y1) ATP receptors which occur in the CNS are activated selectively by naturally-occurring adenine dinucleotides which are known to be released with nucleotides from storage vesicles. The observed potentiation of P2X2-responses by Ap5A, where co-released with ATP by brain synaptosomes, may have a functional bearing in purinergic signalling in the CNS.     

Evidence for the presence of both P1 and P2 purinoceptors in the rat myometrium

1. Adenosine, adenosine triphosphate (ATP) and some stable analogues of adenosine inhibited field stimulation-induced contractions of the uterus from rats treated with oestradiol cypionate (20 micrograms/kg, s.c.) 1 day previously. Adenosine was twice as potent as ATP; both were potentiated by dipyridamole (10 mumol/L). 2. The order of agonist potency of adenosine and its analogues was: 5'-N-ethylcarboxamidoadenosine (NECA) > N6-cyclohexyladenosine > or = R-phenylisopropyladenosine = S-phenylisopropyladenosine = 2-chloroadenosine > or = adenosine > or = ATP > > 2-p-(2-carboxyethyl) phenethylamino-5'-N-ethylcarboxamidoadenosine. This order suggests the presence of P1 purinoceptors of the A2B subtype. 3. Responses to agonists were antagonized to differing extents by the P1 purinoceptor antagonist 8-phenyltheophylline (10 mumol/L). 4. In uterine preparations from rats pretreated for 2 days with oestrogen (20 micrograms/kg, s.c.) and for 1 day with progesterone (3 mg/animal, s.c.), the inhibitory potencies of adenosine and NECA were reduced, indicating hormonal regulation of uterine responsiveness to P1 purinoceptor agonists. 5. Stable analogues of ATP caused contractions of unstimulated myometrial preparations from oestrogen-treated animals, indicating activation of a P2 purinoceptor, possibly of the P2X subtype, because of the relative order of potency was alpha, beta-methylene ATP > beta, gamma-methylene ATP = ATP = 2-methylthio ATP.     

Stress-response-dampening effects of alcohol: Attention as a mediator and moderator.

The present study sought to characterize alcohol's stress-response-dampening (SRD) effects on multiple measures of stress and whether these effects are mediated by reductions in sustained attention and, further, whether baseline levels of sustained attention moderate SRD. One hundred six men consumed either an alcohol (0.70 g/kg) or a placebo beverage prior to learning that they would deliver a self-disclosing speech. Structural equation models controlling for multiple baseline periods indicated that alcohol directly reduced self-reported anxiety and skin conductance levels in response to the stressor. Alcohol's effect on reducing heart rate response, in contrast, was indirect and mediated by effects on prestress baseline. As hypothesized, differences in sustained attention partially mediated the effects of alcohol on skin conductance (but not heart rate or self-reported anxiety) and served as a moderator of alcohol's effects on skin conductance response. Findings are discussed in terms of theoretical links among alcohol consumption, specific cognitive abilities, and stress reactivity. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Mobility as a mediator of the effects of child maltreatment on academic performance

This study examined the role of residential and school mobility as a mediator between child maltreatment and academic outcomes. Using a sample of 711 maltreated and nonmaltreated children ranging from 5 to 15 years old matched on gender, grade, school, and socioeconomic status, path analytic techniques were employed to assess direct and indirect effects of maltreatment on recent achievement test scores, current grades, and grade repetitions. The results indicated that mobility did help account for the effects of maltreatment on each of the outcomes. For grades in English/reading, 32.7% of the effect of maltreatment was accounted for by amount of mobility, while for test scores and grade repetitions the numbers were 14.6% and 19.1%, respectively.     

Evidence that P2X purinoceptors mediate the excitatory effects of alphabetamethylene-ADP in rat locus coeruleus neurones

Extracellular and whole-cell patch clamp recordings were used to study the excitatory responses elicited by purine nucleotides in pontine slices of the rat brain containing the locus coeruleus (LC). The P2 purinoceptor agonists, alphabeta-methyleneadenosine 5'-triphosphate (alphabetameATP) and adenosine 5'-O-(2-thiodiphosphate) (ADPalphabetaS), and a novel purinoceptor agonist, alphabeta-methyleneadenosine 5'-diphosphate (alphabetameADP), elicited concentration-dependent increases in the spontaneous firing rate over the concentration range (1-300 microM). On vagus nerve or dorsal root preparations alphabetameADP (100 microM) had no agonist activity. In the presence of both alphabetameATP (300 microM), ADPbetaS (300 microM) elicited a further and significant increase in the firing rate of the LC neurones, whilst neither alphabetameATP nor alphabetameADP (300 microM) elicited a further response. The P2 purinoceptor antagonists, suramin (100 microM) and pyridoxalphosphate-6-azophenyl-2',4'-disulphonic acid (PPADS; 30 microM), markedly attenuated responses to all three agonists. Whole-cell recording of membrane current showed that, at - 60 mV, alphabetameATP and alphabetameADP (both 100 microM) elicited inward currents of a similar magnitude, whilst the inward currents elicited by a lower concentration of ADPbetaS (30 microM) were larger and faded in the presence of this agonist. In the presence of tetrodotoxin and a combination of other neurotransmission blockers, both alphabetameATP and alphabetameADP still produced inward currents. Based on the known selectivity of the agonists used in this study, there appear to be two distinct P2 purinoceptor types present on neurones in the LC, which correspond to the P2X and P2Y types. The responses elicited by alphabetameADP appear to be mediated through a putative P2X purinoceptor, although further work is required to determine which P2X receptor subtype(s) are involved.     

Coping as a mediator of emotion.

There is widespread conviction among health care professionals that coping affects emotion. Yet theory and research have traditionally emphasized the effects of emotion on coping. The present research addresses this imbalance by evaluating the extent to which coping mediated emotions during stressful encounters in two Caucasian, community-residing samples. Subjects' recently experienced stressful encounters, the ways they coped with the demands of those encounters, and the emotions they experienced during two stages of those encounters were assessed repeatedly. The extent to which eight forms of coping mediated each of four sets of emotions was evaluated with a series of hierarchical regression analyses (of residuals). Coping was associated with changes in all four sets of emotions, with some forms of coping associated with increases in positive emotions and other forms associated with increases in negative emotions. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Differential heterologous and homologous desensitization of two receptors for ATP (P2y purinoceptors and nucleotide receptors) coexisting on endothelial cells

Bovine aortic endothelial cells in culture contain two coexisting phosphoinositidase C-linked receptors for ATP, the P2y-purinoceptors [for which 2-methylthio-ATP (2MeSATP) is a selective agonist] and the nucleotide (or P2u) receptors (for which UTP is a selective agonist). Here we have investigated the occurrence of homologous and heterologous desensitization of these two receptors and the involvement of protein kinase C-dependent mechanisms. Measuring total [3H]inositol (poly)phosphate accumulation in the presence of lithium, we showed that with long (15-min) stimulations with UTP or 2MeSATP desensitization occurred to a maximum of 40% within several minutes of preexposure to either agonist, i.e., with this procedure there is no difference between the heterologous and the homologous experimental design. In the remainder of the experiments reported we measured inositol-1,4,5-trisphosphate mass levels, using a protocol of 5-min preincubation, 2-min wash, and 5-sec stimulation. We found that preincubation with either agonist led to desensitization of the response to the same agonist of about 40%. However, whereas preincubation with 2MeSATP did not affect the subsequent response to UTP, preincubation with UTP did attenuate the 2MeSATP response. These results demonstrate that homologous desensitization occurs with both P2Y and nucleotide receptors but that heterologous desensitization follows only from activation of the nucleotide receptors. Preincubation with the protein kinase C inhibitor Ro 31-8220 enhanced the subsequent inositol-1,4,5-trisphosphate response to 2MeSATP but did not affect the desensitization of this response by preincubation with the same agonist. However, whereas the response to UTP was not enhanced by preincubation with the protein kinase C inhibitor, the desensitization caused by preincubation with UTP was partially inhibited by Ro 31-8220. These results show that multiple desensitizing events occur during the first few minutes of receptor activation and that these events are different for each of the receptors for ATP.     

Purinoceptors: are there families of P2X and P2Y purinoceptors?

There has been an exponential growth in interest in purinoceptors since the potent effects of purines were first reported in 1929 and purinoceptors defined in 1978. A distinction between P1 (adenosine) and P2 (ATP/ADP) purinoceptors was recognized at that time and later, A1 and A2, as well as P2x and P2y subclasses of P1 and P2 purinoceptors were also defined. However, in recent years, many new subclasses have been claimed, particularly for the receptors to nucleotides, including P2t, P2z, P2u(n) and P2D, and there is some confusion now about how to incorporate additional discoveries concerning the responses of different tissues to purines. The studies beginning to appear defining the molecular structure of P2-purinoceptor subtypes are clearly going to be important in resolving this problem, as well as the introduction of new compounds that can discriminate pharmacologically between subtypes. Thus, in this review, on the basis of this new data and after a detailed analysis of the literature, we propose that: (1) P2X(ligand-gated) and P2Y(G-protein-coupled) purinoceptor families are established; (2) four subclasses of P2X-purinoceptor can be identified (P2X1-P2X4) to date; (3) the variously named P2-purinoceptors that are G-protein-coupled should be incorporated into numbered subclasses of the P2Y family. Thus: P2Y1 represents the recently cloned P2Y receptor (clone 803) from chick brain; P2Y2 represents the recently cloned P2u (or P2n) receptor from neuroblastoma, human epithelial and rat heart cells; P2Y3 represents the recently cloned P2Y receptor (clone 103) from chick brain that resembles the former P2t receptor; P2Y4-P2Y6 represent subclasses based on agonist potencies of newly synthesised analogues; P2Y7 represents the former P2D receptor for dinucleotides. This new framework for P2 purinoceptors would be fully consistent with what is emerging for the receptors to other major transmitters, such as acetylcholine, gamma-aminobutyric acid, glutamate and serotonin, where two main receptor families have been recognised, one mediating fast receptor responses directly linked to an ion channel, the other mediating slower responses through G-proteins. We fully expect discussion on the numbering of the different receptor subtypes within the P2X and P2Y families, but believe that this new way of defining receptors for nucleotides, based on agonist potency order, transduction mechanisms and molecular structure, will give a more ordered and logical approach to accommodating new findings. Moreover, based on the extensive literature analysis that led to this proposal, we suggest that the development of selective antagonists for the different P2-purinoceptor subtypes is now highly desirable, particularly for therapeutic purposes.     

Partner support as a mediator of intervention outcome

Following up on previous work demonstrating that an intervention with at-risk mothers made a positive impact on the quality of mothers' partner support, responsiveness to the needs of the child, the child's expectation of being cared for, and child's response to a brief separation, the present paper examines whether quality of the mother's partner support mediated the impact of the intervention on these outcomes.     

Exercise as a mediator of psychological and nutritional effects of testosterone therapy in HIV+ men

PURPOSE: The purpose of this study was to determine whether exercise mediates the psychological and nutritional effects of testosterone therapy in men with symptomatic HIV illness, low serum testosterone, and clinical symptoms of hypogonadism. METHODS: A 12-wk open trial of biweekly intramuscular testosterone injections was conducted, with 54 men completing the trial and exercise assessments. Most (71%) men were diagnosed with AIDS; 41% had a CD4 < 50. One-third of the men were diagnosed with major depression, and nearly half had some evidence of wasting. Twenty-nine men (54%) engaged in exercise (predominantly resistance training) during the trial. Exercisers did not differ from nonexercisers on any measure of psychological well being or nutritional status at baseline. RESULTS: After 12 wk of testosterone treatment, those who exercised showed significant improvement in mood (Hamilton Rating Scale for Depression; HAM-D) and overall distress (Brief Symptom Inventory; BSI) (P < 0.000 for both), as well as a significant increase in body cell mass (P < 0.01) and lean body mass (mean increase of 2.6 kg; P < 0.000) as measured by bioelectric impedance analysis. In contrast, nonexercisers showed improvement on the HAM-D (P < 0.000), but not the BSI or measures of nutritional status. CONCLUSION: These findings indicate that exercise may be an important adjunct to testosterone therapy in the treatment of psychological distress and wasting symptoms in men with symptomatic HIV illness.     

The alliance as mediator of expectancy effects in short-term individual therapy.

The authors investigated the hypothesis that the therapeutic alliance mediates the relationship between pretherapy expectancy of improvement and psychotherapy outcome. Data were drawn from a comparative trial of 2 forms of short-term, time-limited individual psychotherapy (W. E. Piper, A. S. Joyce. M. McCallum, & H. F. Azim, 1998). Measures of expectancy and outcome were based on an individualized assessment of target objectives; outcome was considered from 3 perspectives (patient, independent assessor, therapist). Using the R. M. Baron and D. A. Kenny (1986) procedure, the authors, found evidence in support of the hypothesized mediation effect. The effect was evident when the alliance was rated from the perspective of either patient or therapist, and it accounted for one third of the direct impact of expectancy on outcome. Clinical implications and limitations of the study are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Potential role of WAF1/Cip1/p21 as a mediator of TGF-beta cytoinhibitory effect

Transforming growth factor-beta (TGF-beta) inhibits cell cycle progression of many types of human cells by arresting them in the G1 phase of the cell cycle. The arrest is mediated through interactions of various cyclin-dependent protein kinases (CDKs) and their inhibitors. We demonstrate that treatment with TGF-beta induces increased levels of WAF1/Cip1/p21, a potent inhibitor of various cyclin-CDK kinase activities, in two colon cancer cell lines (LS1034 and LS513), which are sensitive to TGF-beta-induced growth arrest. The induction in at least one of these cell lines (LS1034,p53-) is p53-independent. No WAF1 induction was observed after TGF-beta treatment in a third cell line (HT-29), which is completely insensitive to the cytoinhibitory effect of TGF-beta. In both LS513 and LS1034, WAF1 induction correlated with reduced cyclin E-associated kinase activity in vitro and suppression of the retinoblastoma susceptibility gene (Rb) protein phosphorylation in vivo. In addition, WAF1 was physically associated with cyclin E in the two sensitive cell lines. These results suggest that WAF1/Cip1/p21 is a mediator of cellular sensitivity to TGF-beta.     

Mood as a mediator of place dependent memory.

Converging evidence from 3 studies suggests that how well information transfers from one environment to another depends on how similar the environments feel rather than on how similar they look. Thus, even when target events are encoded and retrieved in the same physical setting, memory performance suffers if the attending affective states differ. Conversely, a change in environment produces no performance decrement if, whether by chance (Experiments 1 and 2) or by design (Experiment 3), the mood at encoding matches the mood at retrieval. These observations imply that place dependent effects are mediated by alterations in affect or mood, and that data that appear on the surface to demonstrate place dependent memory may, at a deeper level, denote the presence of mood dependent memory. Discussion focuses on prospects for future research aimed at clarifying the relations among moods, places, and memory. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine as a substrate of cytochrome P450 2D6: allosteric effects of NADPH-cytochrome P450 reductase

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), a neurotoxin that produces Parkinsonism symptoms in man, has been examined as a substrate of recombinant human cytochrome P450 2D6. When cumene hydroperoxide is used as an oxygen and electron donor, a single product is formed, identified as 4-phenyl-1,2,3,6-tetrahydropyridine. The K(m) for formation of this product (130 microM) is in agreement with the dissociation constants for MPTP binding to the enzyme determined by optical and nuclear magnetic resonance (NMR) spectroscopy. When the reaction is carried out with nicotinamide adenine dinucleotide phosphate (reduced) (NADPH) and recombinant human NADPH-cytochrome P450 reductase, a second product, identified as 1-methyl-4-(4'-hydroxyphenyl)-1,2,3,6-tetrahydropyridine, is formed in addition to 4-phenyl-1,2,3,6-tetrahydropyridine. The K(m) values for formation of these two products are 19 microM and 120 microM, respectively. Paramagnetic relaxation experiments have been used to measure distances between the protons of bound MPTP and the heme iron, and these have been used to construct models for the position and orientation of MPTP in the active site. For the cytochrome alone, a single mode of binding was observed, with the N-methyl close to the heme iron in a position appropriate for the observed N-demethylation reaction. In the presence of the reductase, the data were not consistent with a single mode of binding but could be explained by the existence of two alternative orientations of MPTP in the active site. One of these, characterized by a dissociation constant of 150 microM, is essentially identical to that observed in the absence of the reductase. In the second, which has a K(d) of 25 microM, the MPTP is oriented so that the aromatic ring is close to the heme iron, in a position appropriate for p-hydroxylation leading to the formation of the product seen only in the presence of the reductase. In the case of codeine, another substrate for cytochrome P450 2D6, the addition of reductase had no effect on the nature of the product formed, the dissociation constant, or the orientation in the binding site. These observations show that NADPH-cytochrome P450 reductase has an allosteric effect on the active site of cytochrome P450 2D6 that affects the binding of some substrates but not others.     

Analysis of the influence of nucleotidases on the apparent activity of exogenous ATP and ADP at P2Y1 receptors

The multifunctional cytokine interleukin-1 (IL-1) is a key mediator in the cytokine network. The IL-1 family consists of two zymogen isoforms of IL-1 (IL-1alpha and IL-1beta), the IL-1 receptor antagonists, two receptors and receptor-associated proteins. Identification of the enzyme responsible for cleavage and activation of the IL-1beta precursor, the IL-1beta converting enzyme (ICE; caspase 1), unexpectedly linked the IL-1 family to the apoptosis machinery, since ICE is the founding molecule of the caspase family, which is important for regulation of apoptosis. Although it has been suggested that cytokines are involved in pathogenesis of cardiovascular diseases only few informations exist regarding the endogenous production and function of IL-1 and the associated enzyme(s) of the caspase family in the cardiovascular system. Here, we summarize informations regarding the IL-1 and the caspase family in the cardiovascular system.     

ATP1AL1, a member of the non-gastric H,K-ATPase family, functions as a sodium pump

The human ATP1AL1-encoded protein (an alpha subunit of the human non-gastric H,K-ATPase) has previously been shown to assemble with the gastric H,K-ATPase beta subunit (gH,Kbeta) to form a functionally active ionic pump in HEK 293 cells. This pump has been found to be sensitive to both SCH 28080 and ouabain. However, the 86Rb+-influx mediated by the ATP1AL1-gH,Kbeta heterodimer in HEK 293 cells is at least 1 order of magnitude larger than the maximum ouabain-sensitive proton efflux detected in the same cells. In this study we find that the intracellular Na+ content in cells expressing ATP1AL1 and gH,Kbeta is two times lower than that in control HEK 293 cells in response to incubation for 3 h in the presence of 1 microM ouabain. Moreover, analysis of net Na+ efflux in HEK 293 expressing the ATP1AL1-gH,Kbeta heterodimer reveals the presence of Na+ extrusion activity that is not sensitive to 1 microM ouabain but can be inhibited by 1 mM of this drug. In contrast, ouabain-inhibitable Na+ efflux in control HEK 293 cells is similarly sensitive to either 1 microM or 1 mM ouabain. Finally, 86Rb+ influx through the ATP1AL1-gH,Kbeta complex is comparable to the 1 mM ouabain-sensitive Na+ efflux in the same cells. The data presented here suggest that the enzyme formed by ATP1AL1 and the gastric H,K-ATPase beta subunit in HEK 293 cells mediates primarily Na+,K+ rather than H+,K+ exchange.