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1.
Caffeine, a stimulant largely consumed around the world, is a non-selective adenosine receptor antagonist, and therefore caffeine actions at synapses usually, but not always, mirror those of adenosine. Importantly, different adenosine receptors with opposing regulatory actions co-exist at synapses. Through both inhibitory and excitatory high-affinity receptors (A1R and A2R, respectively), adenosine affects NMDA receptor (NMDAR) function at the hippocampus, but surprisingly, there is a lack of knowledge on the effects of caffeine upon this ionotropic glutamatergic receptor deeply involved in both positive (plasticity) and negative (excitotoxicity) synaptic actions. We thus aimed to elucidate the effects of caffeine upon NMDAR-mediated excitatory post-synaptic currents (NMDAR-EPSCs), and its implications upon neuronal Ca2+ homeostasis. We found that caffeine (30–200 μM) facilitates NMDAR-EPSCs on pyramidal CA1 neurons from Balbc/ByJ male mice, an action mimicked, as well as occluded, by 1,3-dipropyl-cyclopentylxantine (DPCPX, 50 nM), thus likely mediated by blockade of inhibitory A1Rs. This action of caffeine cannot be attributed to a pre-synaptic facilitation of transmission because caffeine even increased paired-pulse facilitation of NMDA-EPSCs, indicative of an inhibition of neurotransmitter release. Adenosine A2ARs are involved in this likely pre-synaptic action since the effect of caffeine was mimicked by the A2AR antagonist, SCH58261 (50 nM). Furthermore, caffeine increased the frequency of Ca2+ transients in neuronal cell culture, an action mimicked by the A1R antagonist, DPCPX, and prevented by NMDAR blockade with AP5 (50 μM). Altogether, these results show for the first time an influence of caffeine on NMDA receptor activity at the hippocampus, with impact in neuronal Ca2+ homeostasis. 相似文献
2.
The highly potent but modestly selective N-(2-amino-4-methoxy-benzothiazol-7-yl)- N-ethyl-acetamide derivative 2 was selected as the starting point for the design of novel selective A 2B antagonists, due to its excellent potency, and good drug-like properties. A series of compounds containing nonaromatic amides or ureas of five- or six-membered rings, and also bearing an m-trifluoromethyl-phenyl group (shown to impart superior potency) was prepared and evaluated for their selectivity against the A 2A and A 1 receptors. This work resulted in the identification of compound 30, with excellent potency and high selectivity against both A 2A and A 1 receptors. 相似文献
3.
A 2A adenosine receptor (A 2AR), P2Y 1 receptor (P2Y 1R) and P2Y 12 receptor (P2Y 12R) are predominantly expressed on human platelets. The individual role of each of these receptors in platelet aggregation has been actively reported. Previously, hetero-oligomerization between these three receptors has been shown to occur. Here, we show that Ca 2+ signaling evoked by the P2Y 1R agonist, 2-methylthioladenosine 5’ diphosphate (2MeSADP) was significantly inhibited by the A 2AR antagonist (ZM241385 and SCH442416) and the P2Y 12R antagonist (ARC69931MX) using HEK293T cells expressing the three receptors. It was confirmed that inhibition of P2Y 1R signaling by A 2AR and P2Y 12R antagonists was indeed mediated through A 2AR and P2Y 12R using 1321N1 human astrocytoma cells which do not express P2Y receptors. We expect that intermolecular signal transduction and specific conformational changes occur among components of hetero-oligomers formed by these three receptors. 相似文献
4.
Endothelin is one of the most potent vasoconstrictors known. It plays an important role in the regulation of vascular tone and in the development of many cardiovascular diseases. This study focuses on the receptor types and the Ca 2+ mobilization responsible for endothelin-1 (ET-1) contraction in de-endothelialized pig coronary artery rings. ET-1 contracted the artery rings with an EC 50 = 6.5 ± 1 nM and a maximum contraction which was 98.6 ± 9% of the contraction produced by 60 mM KCl. BQ123 (5 µM), an ET A antagonist, reversed 78 ± 3% of the ET-1 contraction (50 nM). IRL1620, a selective ET B agonist, produced 23 ± 3% of the total ET-1 contraction with an EC 50 = 12.7 ± 2 nM. More than 85% of the contraction due to 100 nM IRL 1620 was inhibited by 200 nMBQ788, an ET B antagonist. Therefore, approximately 80% of the ET-1 contraction in this artery occurred via ET A receptors, and the other 20% was mediated by ET B receptors. To assess the Ca 2+ pools utilized during the ET-1 response, ET-1 contraction was also examined in medium containing an L-type Ca 2+ channel blocker nitrendipine, and in Ca 2+ free medium containing 0.2 mM EGTA. In Ca 2+ containing medium the contraction elicited by ET-1 was 98.6 ± 9% of the KCl contraction, however, in the presence 10 µM nitrendipine the ET-1 induced contraction was 54 ± 7% of the KCl contraction, and in Ca 2+-free medium it was 13 ± 2%. Similarly, the IRL 1620 contractions in Ca 2+ containing medium, in the presence of nitrendipine and in Ca 2+-free medium were 22.4 ± 3%, 12 ± 3% and 11 ± 2% of the KCl response respectively. Thus, both ET A and ET B contractions utilize extracellular Ca 2+ pools via L-type Ca 2+ channels and other undefined route(s), as well as intracellular Ca 2+ pools. In the pig coronary artery smooth muscle, ET-1 contractions occur predominantly via ET A receptors, with ET B receptors using similar Ca 2+ mobilization pathways, but the ET B receptors appear to use the intracellular Ca 2+ stores to a greater extent. 相似文献
5.
Adenosine A 2A receptors (A 2ARs) and dopamine D 2 receptors (D 2Rs) form constitutive heteromers in living cells and exhibit a strong functional antagonistic interaction. Recent findings give neurochemical evidence that extended cocaine self-administration in the rat give rise to an up-regulation of functional A 2ARs in the nucleus accumbens that return to baseline expression levels during cocaine withdrawal. In the present work, the acute in vitro effects of a concentration of cocaine known to fully block the dopamine (DA) transporter without exerting any toxic actions were investigated on A 2AR and D 2LR formed heteromers in transiently co-transfected HEK-293T cells. In vitro treatment of cocaine was found to produce changes in D 2R homodimers and in A 2AR-D 2R heterodimers detected through bioluminescent energy transfer (BRET). Cocaine was found to produce a time- and concentration-dependent reduction in the BRET max between A 2AR-D 2LR heterodimers and D 2LR homodimers, but not A 2AR homodimers, indicating its effect on D 2R. Cocaine was evaluated with regard to D 2R binding using a human D 2LR stable expressing CHO cell line and was found to produce an increase in the affinity of hD 2LR for DA. At the level of G protein-coupling, cocaine produced a small, but significant increase in DA-stimulated binding of GTPγS. However, cocaine failed to modulate D 2R agonist-induced inhibition of cAMP in stable hD 2LR CHO cells or the gating of GIRK channels in oocytes. Taken together, these results indicate a direct and specific effect of a moderate concentration of cocaine on the DA D 2LR, that results in enhanced agonist recognition, G protein-coupling and an altered conformational state of D 2R homodimers and A 2AR-D 2R heterodimers. 相似文献
6.
Using fura-2-acetoxymethyl ester (AM) fluorescence imaging and patch clamp techniques, we found that endothelin-1 (ET-1) significantly
elevated the intracellular calcium level ([Ca 2+] i) in a dose-dependent manner and activated the L-type Ca 2+ channel in cardiomyocytes isolated from rats. The effect of ET-1 on [Ca 2+] i elevation was abolished in the presence of the ET A receptor blocker BQ123, but was not affected by the ET B receptor blocker BQ788. ET-1-induced an increase in [Ca 2+] i, which was inhibited 46.7% by pretreatment with a high concentration of ryanodine (10 μmol/L), a blocker of the ryanodine
receptor. The ET-1-induced [Ca 2+] i increase was also inhibited by the inhibitors of protein kinase A (PKA), protein kinase C (PKC) and angiotensin type 1 receptor
(AT1 receptor). We found that ET-1 induced an enhancement of the amplitude of the whole cell L-type Ca 2+ channel current and an increase of open-state probability (NPo) of an L-type single Ca 2+ channel. BQ123 completely blocked the ET-1-induced increase in calcium channel open-state probability. In this study we demonstrated
that ET-1 regulates calcium overload through a series of mechanisms that include L-type Ca 2+ channel activation and Ca 2+-induced Ca 2+ release (CICR). ETA receptors, PKC, PKA and AT1 receptors may also contribute to this pathway.
Supported by the National Natural Science Foundation of China (Grant No. 200830870910). 相似文献
7.
Depolarization-evoked increases in intraterminal free Ca 2+ are required for the induction of neurotransmitter release from nerve terminals. Although the mechanisms that regulate the voltage-induced accumulation of presynaptic Ca 2+ remain obscure, there is evidence that the phospholipase-dependent accumulation of arachidonic acid, or its metabolites, may be involved. Therefore, fura-2 loaded hippocampal mossy fiber nerve endings were used to investigate the relationships between membrane depolarization, lipid metabolism and presynaptic Ca 2+ availability. It was observed that depolarization of the nerve terminals with KCl induced an increase in intraterminal free calcium that was inhibited more than 90% by a combination of voltage-sensitive Ca 2+ channel blockers. In addition, the K +-dependent effects on Ca 2+ concentrations were attenuated in the presence of phospholipase A 2 inhibitors, but were mimicked by the phospholipase A 2 activator melittin and exogenous arachidonic acid. Both the melittin- and arachidonic acid-induced increases in presynaptic Ca 2+ were reduced by voltage-sensitive Ca 2+ channel blockers. The stimulatory effects of arachidonic acid appeared to be independent of its further metabolism to prostaglandins. In fact, inhibition of either cyclooxygenase or lipoxygenase pathways resulted in a potentiation of the depolarization-evoked increase in intraterminal free Ca 2+. From these results, we propose that some portion of the depolarization-evoked increase in intraterminal free calcium depends on the activation of phospholipase A 2 and the subsequent accumulation of unesterified arachidonic acid. 相似文献
8.
Autophagy is a cellular process responsible for delivery of proteins or organelles to lysosomes. It participates not only in maintaining cellular homeostasis, but also in promoting survival during cellular stress situations. It is now well established that intracellular Ca 2+ is one of the regulators of autophagy. However, this control of autophagy by intracellular Ca 2+ signaling is the subject of two opposite views. On the one hand, the available evidence indicates that intracellular Ca 2+ signals, and mainly inositol 1,4,5-trisphosphate receptors (IP 3Rs), suppress autophagy. On the other hand, elevated cytosolic Ca 2+ concentrations ([Ca 2+] cyt) were also shown to promote the autophagic process. Here, we will provide a critical overview of the literature and discuss both hypotheses. Moreover, we will suggest a model explaining how changes in intracellular Ca 2+ signaling can lead to opposite outcomes, depending on the cellular state. 相似文献
9.
Ca V1 and Ca V2 voltage-gated calcium channels evolved from an ancestral Ca V1/2 channel via gene duplication somewhere near the stem animal lineage. The divergence of these channel types led to distinguishing functional properties that are conserved among vertebrates and bilaterian invertebrates and contribute to their unique cellular roles. One key difference pertains to their regulation by calmodulin (CaM), wherein bilaterian Ca V1 channels are uniquely subject to pronounced, buffer-resistant Ca 2+/CaM-dependent inactivation, permitting negative feedback regulation of calcium influx in response to local cytoplasmic Ca 2+ rises. Early diverging, nonbilaterian invertebrates also possess Ca V1 and Ca V2 channels, but it is unclear whether they share these conserved functional features. The most divergent animals to possess both Ca V1 and Ca V2 channels are placozoans such as Trichoplax adhaerens, which separated from other animals over 600 million years ago shortly after their emergence. Hence, placozoans can provide important insights into the early evolution of Ca V1 and Ca V2 channels. Here, we build upon previous characterization of Trichoplax Ca V channels by determining the cellular expression and ion-conducting properties of the Ca V1 channel orthologue, TCa V1. We show that TCa V1 is expressed in neuroendocrine-like gland cells and contractile dorsal epithelial cells. In vitro, this channel conducts dihydropyridine-insensitive, high-voltage–activated Ca 2+ currents with kinetics resembling those of rat Ca V1.2 but with left-shifted voltage sensitivity for activation and inactivation. Interestingly, TCa V1, but not TCa V2, exhibits buffer-resistant Ca 2+/CaM-dependent inactivation, indicating that this functional divergence evolved prior to the emergence of bilaterian animals and may have contributed to their unique adaptation for cytoplasmic Ca 2+ signaling within various cellular contexts. 相似文献
10.
Docosahexaenoic acid (DHA) and arachidonic acid (AA) are found in high concentrations in brain cell membranes and are important for brain function and structure. Studies suggest that AA and DHA are hydrolyzed selectively from the sn-2 position of synaptic membrane phospholipids by Ca 2+-dependent cytosolic phospholipase A 2 (cPLA 2) and Ca 2+-independent phospholipase A 2 (iPLA 2), respectively, resulting in increased levels of the unesterified fatty acids and lysophospholipids. Cell studies also suggest that AA and DHA release depend on increased concentrations of Ca 2+, even though iPLA 2 has been thought to be Ca 2+-independent. The source of Ca 2+ for activation of cPLA 2 is largely extracellular, whereas Ca 2+ released from the endoplasmic reticulum can activate iPLA 2 by a number of mechanisms. This review focuses on the role of Ca 2+ in modulating cPLA 2 and iPLA 2 activities in different conditions. Furthermore, a model is suggested in which neurotransmitters regulate the activity of these enzymes and thus the balanced and localized release of AA and DHA from phospholipid in the brain, depending on the primary source of the Ca 2+ signal. 相似文献
11.
T-type Ca 2+ channels have been implicated in tremorogenesis and motor coordination. The α1 subunit of the Ca V3.1 T-type Ca 2+ channel is highly expressed in motor pathways in the brain, but knockout of the Ca V3.1 gene (α1G -/-) per se causes no motor defects in mice. Thus, the role of Ca V3.1 channels in motor control remains obscure in vivo. Here, we investigated the effect of the Ca V3.1 knockout in the null genetic background of α1 GABA A receptor (α1 −/−) by generating the double mutants (α1 −/−/α1G -/-). α1 −/−/α1G -/- mice showed severer motor abnormalities than α1 −/− mice as measured by potentiated tremor activities at 20 Hz and impaired motor learning. Propranolol, an anti-ET drug that is known to reduce the pathologic tremor in α1 −/− mice, was not effective for suppressing the potentiated tremor in α1 −/−/α1G -/- mice. In addition, α1 −/−/α1G -/- mice showed an age-dependent loss of cerebellar Purkinje neurons. These results suggest that α1 −/−/α1G -/- mice are a novel mouse model for a distinct subtype of ET in human and that Ca V3.1 T-type Ca 2+ channels play a role in motor coordination under pathological conditions. 相似文献
12.
Evidence exists that the adenosine receptor A 2AR and the dopamine receptor D 2R form constitutive heteromers in living cells. Mass spectrometry and pull-down data showed that an arginine-rich domain of the D 2R third intracellular loop binds via electrostatic interactions to a specific motif of the A 2AR C-terminal tail. It has been indicated that the phosphorylated serine 374 might represent an important residue in this motif. In the present study, it was found that a point mutation of serine 374 to alanine reduced the A 2AR ability to interact with D 2R. Also, this point mutation abolished the A 2AR-mediated inhibition of both the D 2R high affinity agonist binding and signaling. These results point to a key role of serine 374 in the A 2AR-D 2R interface. All together these results indicate that by targeting A 2AR serine 374 it will be possible to allosterically modulate A 2AR-D 2R function, thus representing a new approach for therapeutically modulate D 2R function. 相似文献
13.
Primary lens epithelial cell (LEC) cultures derived from newborn (P0) and one-month-old (P30) mouse lenses were used to study GABA (gamma-aminobutyric acid) signaling expression and its effect on the intracellular Ca 2+ ([Ca 2+] i) level. We have found that these cultures express specific cellular markers for lens epithelial and fiber cells, all components of the functional GABA signaling pathway and GABA, thus recapitulating the developmental program of the ocular lens. Activation of both GABA-A and GABA-B receptors (GABA AR and GABA BR) with the specific agonists muscimol and baclofen, respectively induces [Ca 2+] i transients that could be blocked by the specific antagonists bicuculline and CGP55845 and were dependent on extracellular Ca 2+. Bicuculline did not change the GABA-evoked Ca 2+ responses in Ca 2-containing buffers, but suppressed them significantly in Ca 2+-free buffers suggesting the two receptors couple to convergent Ca 2+ mobilization mechanisms with different extracellular Ca 2+ sensitivity. Prolonged activation of GABA BR induced wave propagation of the Ca 2+ signal and persistent oscillations. The number of cells reacting to GABA or GABA + bicuculline in P30 mouse LEC cultures expressing predominantly the synaptic type GABA AR did not differ significantly from the number of reacting cells in P0 mouse LEC cultures. The GABA-induced Ca 2+ transients in P30 (but not P0) mouse LEC could be entirely suppressed by co-application of bicuculline and CGP55845. The GABA-mediated Ca 2+ signaling may be involved in a variety of Ca 2+-dependent cellular processes during lens growth and epithelial cell differentiation. 相似文献
14.
Adenosine A 2a receptor (A 2aR) colocalizes with dopamine D 2 receptor (D 2R) in the basal ganglia and modulates D 2R-mediated dopaminergic activities. A 2aR and D 2R couple to stimulatory and inhibitory G proteins, respectively. Their opposing roles in regulating neuronal activities, such as locomotion and alcohol consumption, are mediated by their opposite actions on adenylate cyclase, which often serves as “co-incidence detector” of various activators. On the other hand, the neural actions of A 2aR and D 2R are also, at least partially, independent of each other, as indicated by studies using D 2R and A 2aR knock-out mice. Here we co-expressed human A 2aR and human D 2LR in CHO cells and examined their signaling characteristics. Human A 2aR desensitized rapidly upon agonist stimulation. A 2aR activity (80%) was diminished after 2 hr of pretreatment with its agonist CGS21680. In contrast, human D 2LR activity was sustained even after 2 hr and 18 hr pretreatment with its agonist quinpirole. Long-term (18 hr) stimulation of human D 2LR also increased basal cAMP levels in CHO cells, whereas long-term (18 hr) activation of human A 2aR did not affect basal cAMP levels. Furthermore, long-term (18 hr) activation of D 2LR dramatically sensitized A 2aR-induced stimulation of adenylate cyclase in a pertussis toxin-sensitive way. Forskolin-induced cAMP accumulation was significantly increased after short-term (2 hr) human D 2LR stimulation and further elevated after long-term (18 hr) D 2LR activation. However, neither short-term (2 hr) nor long-term (18 hr) stimulation of A 2aR affected the inhibitory effects of D 2LR on adenylate cyclase. Co-stimulation of A 2aR and D 2LR could not induce desensitization or sensitization of D 2LR either. In summary, signaling t hrough A 2aR and D 2LR is distinctive and synergistic, supporting their unique and yet integrative roles in regulating neuronal functions when both receptors are present. 相似文献
15.
Here we elaborated an analytical approach for the simulation of dose-response curves mediated by cellular receptors coupled to PLC and Ca 2+ mobilization. Based on a mathematical model of purinergic Ca 2+ signaling in taste cells, the analysis of taste cells responsiveness to nucleotides was carried out. Consistently with the expression of P2Y 2 and P2Y 4 receptors in taste cells, saturating ATP and UTP equipotently mobilized intracellular Ca 2+. Cellular responses versus concentration of BzATP, a P2Y 2 agonist and a P2Y 4 antagonist, implicated high and low affinity BzATP receptors. Suramin modified the BzATP dose-response curve in a manner that suggested the low affinity receptor to be weakly sensitive to this P2Y antagonist. Given that solely P2Y 2 and P2Y 11 are BzATP receptors, their high sensitivity to suramin is poorly consistent with the suramin effects on BzATP responses. We simulated a variety of dose-response curves for different P2Y receptor sets and found that the appropriate fit of the overall pharmacological data was achievable only with dimeric receptors modeled as P2Y 2/P2Y 4 homo- and heterodimers. Our computations and analytical analysis of experimental dose-response curves raise the possibility that ATP responsiveness of mouse taste cells is mediated by P2Y 2 and P2Y 4 receptors operative mostly in the dimeric form. 相似文献
16.
Biased agonism describes a multistate model of G protein-coupled receptor activation in which each ligand induces a unique structural conformation of the receptor, such that the receptor couples differentially to G proteins and other intracellular proteins. P2Y receptors are G protein-coupled receptors that are activated by endogenous nucleotides, such as adenosine 5′-triphosphate (ATP) and uridine 5′-triphosphate (UTP). A previous report suggested that UTP may be a biased agonist at the human P2Y 11 receptor, as it increased cytosolic [Ca 2+], but did not induce accumulation of inositol phosphates, whereas ATP did both. The mechanism of action of UTP was unclear, so the aim of this study was to characterise the interaction of UTP with the P2Y 11 receptor in greater detail. Intracellular Ca 2+ was monitored in 1321N1 cells stably expressing human P2Y 11 receptors using the Ca 2+-sensitive fluorescent indicator, fluo-4. ATP evoked a rapid, concentration-dependent rise in intracellular Ca 2+, but surprisingly, even high concentrations of UTP were ineffective. In contrast, UTP was slightly, but significantly more potent than ATP in evoking a rise in intracellular Ca 2+ in 1321N1 cells stably expressing the human P2Y 2 receptor, with no difference in the maximum response. Thus, the lack of response to UTP at hP2Y 11 receptors was not due to a problem with the UTP solution. Furthermore, coapplying a high concentration of UTP with ATP did not inhibit the response to ATP. Thus, contrary to a previous report, we find no evidence for an agonist action of UTP at the human P2Y 11 receptor, nor does UTP act as an antagonist. 相似文献
17.
Adenosine A 2B receptors of native human and rodent cell lines were investigated using [ 3H]PSB-298 [(8-{4-[2-(2-hydroxyethylamino)-2-oxoethoxy]phenyl}-1-propylxanthine] in radioligand binding studies. [ 3H]PSB-298 showed saturable and reversible binding. It exhibited a K D value of 60 ± 1 nM and limited capacity (B max = 3.511 fmol per milligram protein) at recombinant human adenosine A 2B receptors expressed in human embryonic kidney cells (HEK-293). The addition of sodium chloride (100 mM) led to a threefold increase in the number of binding sites recognized by the radioligand. The curve of the agonist 5′-N-ethylcarboxamidoadenosine (NECA) was shifted to the right in the presence of NaCl, while the curve of the antagonist PSB-298 was shifted to the left, indicating that PSB-298 may be an inverse agonist at A 2B receptors. Adenosine A 2B receptors were shown to be the major adenosine A 2 receptor subtype on the mouse neuroblastoma x rat glioma hybrid cell line NG108-15 cells. Binding studies at rat INS-1 cells (insulin secreting cell line) demonstrated that [ 3H]PSB-298 is a selective radioligand for adenosine A 2B binding sites in this cell line. 相似文献
18.
Contraction and relaxation of urinary bladder smooth muscle cells (UBSMCs) represent the important physiological functions of the bladder. Contractile responses in UBSMCs are regulated by a number of ion channels including big-conductance Ca 2+- activated K + (BK) channels. Great progress has been made in studies of BK channels in UBSMCs. The intent of this review is to summarize recent exciting findings with respect to the functional interactions of BK channels with muscarinic receptors, ryanodine receptors (RyRs) and inositol triphosphate receptors (IP 3Rs) as well as their functional importance under normal and pathophysiological conditions. BK channels are highly expressed in UBSMCs. Activation of muscarinic M 3 receptors inhibits the BK channel activity, facilitates opening of voltage-dependent Ca 2+ (Ca V) channels, and thereby enhances excitability and contractility of UBSMCs. Signaling molecules and regulatory mechanisms involving RyRs and IP 3Rs have a significant effect on functions of BK channels and thereby regulate cellular responses in UBSMCs under normal and pathophysiological conditions including overactive bladders. Moreover, BK channels may represent a novel target for the treatment of bladder dysfunctions. 相似文献
19.
In vitro studies show that docosahexaenoic acid (DHA) can be released from membrane phospholipid by Ca 2+-independent phospholipase A 2 (iPLA 2), Ca 2+-independent plasmalogen PLA 2 or secretory PLA 2 (sPLA2), but not by Ca 2+-dependent cytosolic PLA 2 (cPLA2), which selectively releases arachidonic acid (AA). Since glutamatergic NMDA (N-methyl-D-aspartate) receptor activation allows extracellular Ca 2+ into cells, we hypothesized that brain DHA signaling would not be altered in rats given NMDA, to the extent that in vivo signaling was mediated by Ca 2+-independent mechanisms. Isotonic saline, a subconvulsive dose of NMDA (25 mg/kg), MK-801, or MK-801 followed by NMDA was administered i.p. to unanesthetized rats. Radiolabeled DHA or AA was infused intravenously and their brain incorporation coefficients k*, measures of signaling, were imaged with quantitative autoradiography. NMDA or MK-801 compared with saline did not alter k* for DHA in any of 81 brain regions examined, whereas NMDA produced widespread and significant increments in k* for AA. In conclusion, in vivo brain DHA but not AA signaling via NMDA receptors is independent of extracellular Ca 2+ and of cPLA 2. DHA signaling may be mediated by iPLA 2, plasmalogen PLA 2, or other enzymes insensitive to low concentrations of Ca 2+. Greater AA than DHA release during glutamate-induced excitotoxicity could cause brain cell damage. 相似文献
20.
Benign prostatic hypertrophy has been related with glandular ischemia processes and adenosine is a potent vasodilator agent. This study investigates the mechanisms underlying the adenosine-induced vasorelaxation in pig prostatic small arteries. Adenosine receptors expression was determined by Western blot and immunohistochemistry, and rings were mounted in myographs for isometric force recording. A 2A and A 3 receptor expression was observed in the arterial wall and A 2A-immunoreactivity was identified in the adventitia–media junction and endothelium. A 1 and A 2B receptor expression was not obtained. On noradrenaline-precontracted rings, P1 receptor agonists produced concentration-dependent relaxations with the following order of potency: 5′- N-ethylcarboxamidoadenosine (NECA) = {"type":"entrez-protein","attrs":{"text":"CGS21680","term_id":"878113053","term_text":"CGS21680"}}CGS21680 > 2-Cl-IB-MECA = 2-Cl-cyclopentyladenosine = adenosine. Adenosine reuptake inhibition potentiated both NECA and adenosine relaxations. Endothelium removal and ZM241385, an A 2A antagonist, reduced NECA relaxations that were not modified by A 1, A 2B, and A 3 receptor antagonists. Neuronal voltage-gated Ca 2+ channels and nitric oxide (NO) synthase blockade, and adenylyl cyclase activation enhanced these responses, which were reduced by protein kinase A inhibition and by blockade of the intermediate (IK Ca)- and small (SK Ca)-conductance Ca 2+-activated K + channels. Inhibition of cyclooxygenase (COX), large-conductance Ca 2+-activated-, ATP-dependent-, and voltage-gated-K + channel failed to modify these responses. These results suggest that adenosine induces endothelium-dependent relaxations in the pig prostatic arteries via A 2A purinoceptors. The adenosine vasorelaxation, which is prejunctionally modulated, is produced via NO- and COX-independent mechanisms that involve activation of IK Ca and SK Ca channels and stimulation of adenylyl cyclase. Endothelium-derived NO playing a regulatory role under conditions in which EDHF is non-functional is also suggested. Adenosine-induced vasodilatation could be useful to prevent prostatic ischemia. 相似文献
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