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1.
We warmed the top soil of a mature coniferous forest stand by means of heating cables on control and trenched plots within
24 h by 10°C at 1 cm soil depth (9°C at 5 cm depth) and measured the effect on the autotrophic (R A) and heterotrophic (R H) component of total soil CO 2 efflux (R S). The short time frame of warming enabled us to exclude confounding fluctuations in soil moisture and carbon (C) flow from
the canopy. The results of the field study were backed up by a lab soil incubation experiment. During the first 12 h of warming,
R A strongly responded to soil warming; The Q
10 values were 5.61 and 6.29 for 1 and 5 cm soil depth temperature. The Q
10 values for R A were almost twice as high as the Q
10 values of R H (3.04 and 3.53). Q
10 values above 5 are above reasonable plant physiological values for root respiration. We see interactions of roots, mycorrhizae
and heterotrophic microbes, combined with fast substrate supply to the rhizosphere as an explanation for the high short-term
temperature response of R A. When calculated over the whole duration (24 h) of the field soil-warming experiment, temperature sensitivities of R A and R H were similar (no significant difference at P < 0.05); Q
10 values were 3.16 and 3.96 for R A and 2.94 and 3.35 for R H calculated with soil temperatures at 1 and 5 cm soil depth, respectively. Laboratory incubation showed that different soil
moisture contents of trenched and control plots affected rates of R H, but did not affect the temperature sensitivity of R H. We conclude that a single parameter is sufficient to describe the temperature sensitivity of R S in soil C models which operate on larger temporal and spatial scales. The strong short-term response of R A may be of relevance in soils suspected to experience increasingly strong diurnal temperature variations. 相似文献
2.
Several genotype-by-environment stability measures are in use, but little information exists about their inheritance or genetic
inter-relationships. Among those measures in common use are the linear regression coefficient (b), deviations from regression
(s b), coefficient of determination (R 2), coefficient of phenotypic variation (CPV) and, more recently, interaction principal components (IPCA) of the additive-main-effect-and-multiplicative-interaction
(AMMI) model. Because of the factorial structure of the data, the diallel cross is well suited to study these parameters and
their relationship to quantitative traits. For this study a complete diallel cross, derived by mating eight lines from a broad
based bread wheat breeding population, was grown for several growing seasons at two Ugandan locations, one of which was prone
to yellow rust. Stability parameters and grain yield were measured for each cross. CPV had the highest narrow-sense heritability
(h 2=0.522) followed by IPCA1 of the AMMI (h 2=0.461). Lowest narrow-sense heritabilities were calculated for b and R 2 (h 2=0.150 and 0.100 respectively). There were high additive genetic correlations (r A) between grain yield and CPV (r A=−0.933), grain yield and IPCA1 (r A=0.707), and grain yield and IPCA2 (r A=0.751). The genetic association between CPV and IPCA1 was also high and negative (r A= −0.934). These results suggest that it may be possible to select simultaneously for high and stable grain yield in this
broad-based bread wheat breeding pool by selecting outyielders that exhibit a low CPV.
Received: 25 July 2000 / Accepted: 7 December 2000 相似文献
3.
To investigate annual variation in soil respiration ( R
S) and its components [autotrophic ( R
A) and heterotrophic ( R
H)] in relation to seasonal changes in soil temperature (ST) and soil water content (SWC) in an Abies holophylla stand (stand A) and a Quercus-dominated stand (stand Q), we set up trenched plots and measured R
S, ST and SWC for 2 years. The mean annual rate of R
S was 436 mg CO 2 m −2 h −1, ranging from 76 to 1,170 mg CO 2 m −2 h −1, in stand A and 376 mg CO 2 m −2 h −1, ranging from 82 to 1,133 mg CO 2 m −2 h −1, in stand Q. A significant relationship between R
S and its components and ST was observed over the 2 years in both stands, whereas a significant correlation between R
A and SWC was detected only in stand Q. On average over the 2 years, R
A accounted for approximately 34% (range 17–67%) and 31% (15–82%) of the variation in R
S in stands A and Q, respectively. Our results suggested that vegetation type did not significantly affect the annual mean
contributions of R
A or R
H, but did affect the pattern of seasonal change in the contribution of R
A to R
S. 相似文献
4.
Total ( RTOT) and heterotrophic ( RH) respiration were measured in an intensively managed perennial ryegrass ( Lolium perenne L.) grassland. The overall aim of the study was to partition RTOT into RH and autotrophic respiration ( RA). This was achieved as follows: (1) analyse the effect of air temperature, soil moisture content and leaf area index on RTOT and the influence of soil temperature and soil moisture content on RH; (2) combine these effects into separate empirical models for RTOT and RH and; (3) use these models to determine temporal trends in RTOT and RH and to assess the relative contribution of RH and RA to RTOT. CO 2 fluxes were measured using a vented and thermostatically controlled perspex chamber in conjunction with a portable infrared
gas analyser. RTOT was measured in plots with grass and RH in plots with bare soil. RTOT was related to air temperature and RH to soil temperature using exponential relationships. Both RTOT and RH were related to soil moisture content using lognormal relationships. RTOT was related to leaf area index using a linear relationship. These relationships were combined to produce statistical response
functions that explained 87% and 84% of the variation in RTOT and RH, respectively. These relationships were combined with meteorological and leaf area index data to reconstruct daily and seasonal
fluxes. RTOT values in wintertime were ~4 g C m −2 day −1 increasing to ~10 g C m −2 day −1 in summertime when temperatures and leaf area index were higher and soils were drier. RH has a similar seasonal trend to RTOT but was consistently lower. Wintertime values were ~2 g C m −2 day −1 and increased to ~5 g C m −2 day −1 in summertime. Before day of year 143, and after day of year 259 RH and RA represented 62% and 38% of RTOT, respectively. In the period between these days RH and RA both accounted for 50% of RTOT. In total during 2004 RTOT, RH and RA were 2.34, 1.31 and 1.03 kg C m −2, respectively. 相似文献
5.
The affinity profiles for the bovine adenosine receptors, A 1 and A 2A, of a series of 1,8-naphthyridine derivatives were quantitatively analyzed using physicochemical and structural parameters of the substituents, present at varying positions of the molecules. The derived significant correlation, for bovine A 1 receptor, suggested that a R 1 substituent having a higher van der Waals volume, a R 2 substituent being a hydrogen-bond donor and a R 3 substituent able to transmit a higher field effect are helpful in augmenting the pK i of a compound. Similarly the study, pertaining to bovine A 2A receptor, revealed that a less bulky substituent at R 2 and a strong electron-withdrawing substituent at R 3 are desirable in improving the binding affinity of a compound while substituents at R 1 remain insignificant to any interaction. 相似文献
6.
In 20-year-old longleaf pine, we examined short-term effects of reduced live leaf area ( A
L) via canopy scorching on sap flow ( Q; kg H 2O h −1), transpiration per unit leaf area ( E
L; mm day −1), stem CO 2 efflux ( R
stem; μmol m −2 s −1) and soil CO 2 efflux ( R
soil; μmol m −2 s −1) over a 2-week period during early summer. R
stem and Q were measured at two positions (1.3-m or BH, and base of live crown—BLC), and R
soil was measured using 15 open-system chambers on each plot. E
L before and after treatment was estimated using Q measured at BLC with estimates of A
L before and after scorching. We expected Q to decrease in scorched trees compared with controls resulting from reduced A
L. We expected R
stem at BLC and BH and R
soil to decrease following scorching due to reduced leaf area, which would decrease carbon supply to the stem and roots. Scorching
reduced A
L by 77%. Prior to scorching, Q at BH was similar between scorch and control trees. Following scorching, Q was not different between control and scorch trees; however, E
L increased immediately following scorching by 3.5-fold compared to control trees. Changes in E
L in scorched trees corresponded well with changes in VPD ( D), whereas control trees appeared more decoupled over the 5-day period following treatment. By the end of the study, R
stem decreased to 15–25% in scorched trees at both stem positions compared to control trees. Last, we found that scorching resulted
in a delayed and temporary increase in R
soil rather than a decrease. No change in Q and increased E
L following scorching indicates a substantial adjustment in stomatal conductance in scorched trees . Divergence in R
stem between scorch and control trees suggests a gradual decline in stem carbohydrates following scorching. The absence of a strong
R
soil response is likely due to non-limiting supplies of root starch during early summer . 相似文献
7.
Primula nutans Georgi is widely distributed in hummock-and-hollow wetlands on the Qinghai-Tibetan Plateau. To assess the ecophysiology of
this species in responding to microenvironments, we examined the photosynthetic characteristics and individual carbon gain
of plants growing in different microsites from a hummock-and-hollow wetland on the Qinghai-Tibetan Plateau and under laboratory
conditions. Plants from wetland hummock microsites showed significantly higher light-saturated photosynthetic CO 2 uptake ( A
max) than those from microsites in hollows at a controlled temperature of 15°C in leaf chamber. Leaf dark respiration rate ( R) was only significantly higher in plants from hummocks than hollows at the measuring temperature of 35°C. Optimum temperature
for A
max was 15°C for all plants in the field despite different microsites. In plants growing under laboratory conditions differing
in light and temperature, both A
max and R were significantly higher under higher growth light (photosynthetic photon flux density, PPFD: 800 or 400 μmol m −2 s −1) than low light of 90 μmol m −2 s −1. No statistically significant differences in A
max and R existed in plants differing in growing temperatures. Estimates derived from the photosynthetic parameters of field plants,
and microsite environmental measures including PPFD, air temperature and soil temperature showed that the optimum mean daily
temperature for net daily carbon gain was around 10°C and the net daily carbon gain was largely limited under lower daily
total PPFD. These results suggest that the differences in A
max and R in P. nutans are strongly affected by growing light regimes but not by temperature regimes.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
8.
毛竹林是我国重要的森林资源类型,在森林固碳和林业应对气候变化中具有不可替代的重要作用。由于毛竹林的持续采伐与自我更新特性,在竹林经营过程中,新竹的发育数量和质量成为评价竹林固碳功能变化的决定性因子。利用两因素随机区组设计,排除地形因子等影响,选取施肥和采伐留养方式这两个因素,研究老竹水平和经营措施对2010年和2013年毛竹林新竹发育质量的影响。结果表明:无论2010年还是2013年,新竹平均胸径、株数和碳储量与3年生和5年生老竹的相关性均高于2年生和4年生老竹。新竹碳储量与3年生和5年生老竹碳储量呈线性相关,建立线性回归模型y=0.675x-2.2491,R~2=0.8561,而新竹碳储量与2年生和4年生老竹碳储量相关性较低,线性回归模型为y=-0.1109x+6.7287,R~2=0.0061。不同经营措施实施后,新老竹之间关系发生了很大的改变,新竹平均胸径与老竹的相关性大幅下降,新竹株数和碳储量与老竹几乎没有相关性,新竹碳储量与3年生和5年生老竹碳储量的线性回归模型为y=0.1036x+3.7539,R~2=0.0981,新竹碳储量与2年生和4年生老竹碳储量的线性回归模型为y=-0.0408x+5.9069,R~2=0.0151。不同经营措施的实施对新竹的平均胸径、株数和地上碳储量产生了很大的影响。处理A_1B_2(大量施肥中度采伐中密度留养)、A_2B_2(中等施肥中度采伐中密度留养)和A_3B_2(不施肥中度采伐中密度留养)新竹平均胸径、新竹株数和新竹碳储量都有所增加,新竹平均胸径增幅为:处理A_2B_2(8.78%)A_1B_2(2.43%)A_3B_2(2.06%),新竹株数增幅为:处理A_1B_2(81.0%)A3B2(35.4%)A2B2(15.2%),新竹地上碳储量增幅为:处理A_1B_2(90.8%)A_3B_2(35.7%)A_2B_2(49.7%),而其余处理基本都会减少,说明适度采伐留养最有利于提高毛竹林新竹的发育质量。仅仅从固碳最大化的角度出发,大量施肥中度采伐中密度留养最有利于新竹碳储量的增加,而从培养大径竹材的角度考虑,中等施肥中度采伐中密度留养能收到更好的效果。 相似文献
9.
快速、定量、精确地估算区域森林生物量一直是森林生态功能评价以及碳储量研究的重要问题。该研究基于机载激光雷达(LiDAR)点云与Landsat 8 OLI多光谱数据, 借助江苏省常熟市虞山地区55块调查样地数据, 首先提取并分析了87个特征变量(53个OLI特征变量, 34个LiDAR特征变量)与森林地上、地下生物量的Pearson’s相关系数以进行变量优选, 然后利用多元逐步回归法建立森林生物量估算模型(OLI生物量估算模型和LiDAR生物量估算模型), 并与基于两种数据建立的综合生物量估算模型的结果进行比较, 讨论预测结果及其精确性。结果表明: 3种模型(OLI模型、LiDAR模型和综合模型)在所有样地无区分分析时, 地上和地下生物量的估算精度均达到0.4以上, 基于不同森林类型(针叶林、阔叶林、混交林)分析时地上和地下生物量的估算精度均有明显提高, 达到0.67及以上。利用分森林类型模型估算生物量, 综合生物量估算模型精度(地上生物量: R 2为0.88; 地下生物量: R 2为0.92)优于OLI生物量估算模型(地上生物量: R 2为0.73; 地下生物量: R 2为0.81)和LiDAR生物量估算模型(地上生物量: R 2为0.86; 地下生物量: R 2为0.83)。 相似文献
10.
Abstract Net nitrate uptake rates were measured and the kinetics calculated in non-nodulated Pisum sativum L. cv. Marma and Lemna gibba L. adapted to constant relative rates of nitrate-N additions (R A), ranging from 0.03 to 0.27 d ?1 for Pisum and from 0.05 to 0.40 d ?1 for Lemna, V max of net nitrate uptake (measured in the range 10 to 100 mmol m ?3 nitrate, i.e. ‘system I’) increased with R A in the growth limiting range but decreased when R A exceeded the relative growth rate (RGR), K m was not significantly related to changes in R A. On the basis of previous 13N-flux experiments, it is concluded that the differences in V max at growth limiting R A are attributable to differences in influx rates. Linear relationships between V max and tissue nitrogen concentrations were obtained in the growth limiting range for both species, and extrapolated intercepts relate well with the previously defined minimal nitrogen concentrations for plant growth (Oscarson, Ingemarsson & Larsson, 1989). Analysis of V max for net nitrate uptake on intact plant basis in relation to nitrogen demand during stable, nitrogen limited, growth shows an increased overcapacity at lower R A values in both species, which is largely explained by the increased relative root size at low R A. A balancing nitrate concentration, defined as the steady state concentration needed to sustain the relative rate of increase in plant nitrogen (R N), predicted by R A, was calculated for both species. In the growth limiting range, this value ranges from 3.5 mmol m ?3 (R A 0.03 d ?1) to 44 mmol m ?3 (R A 0.21 d ?1) for Pisum and from 0.2 mmol m ?3 (R A 0.05 d ?1) to 5.4 mmol m ?3 (R A 0.03 d ?1) for Lemna. It is suggested that this value can be used as a unifying measure of the affinity for nitrate, integrating the performance of the nitrate uptake system with nitrate flux and long term growth and demand for nitrogen. 相似文献
12.
Phosphatidylglycerol (PG), containing the unique fatty acid Δ3, trans-16:1-hexadecenoic acid, is a minor but ubiquitous lipid component of thylakoid membranes of chloroplasts and cyanobacteria.
We investigated its role in electron transfers and structural organization of Photosystem II (PSII) by treating Arabidopsis thaliana thylakoids with phospholipase A 2 to decrease the PG content. Phospholipase A 2 treatment of thylakoids (a) inhibited electron transfer from the primary quinone acceptor Q A to the secondary quinone acceptor Q B, (b) retarded electron transfer from the manganese cluster to the redox-active tyrosine Z, (c) decreased the extent of flash-induced
oxidation of tyrosine Z and dark-stable tyrosine D in parallel, and (d) inhibited PSII reaction centres such that electron
flow to silicomolybdate in continuous light was inhibited. In addition, phospholipase A 2 treatment of thylakoids caused the partial dissociation of (a) PSII supercomplexes into PSII dimers that do not have the
complete light-harvesting complex of PSII (LHCII); (b) PSII dimers into monomers; and (c) trimers of LHCII into monomers.
Thus, removal of PG by phospholipase A 2 brings about profound structural changes in PSII, leading to inhibition/retardation of electron transfer on the donor side,
in the reaction centre, and on the acceptor side. Our results broaden the simple view of the predominant effect being on the
Q B-binding site. 相似文献
13.
Characters which are closely linked to fitness often have low heritabilities ( VA/ VP). Low heritabilities could be because of low additive genetic variation ( VA), that had been depleted by directional selection. Alternatively, low heritabilities may be caused by large residual variation ( VR= VP – VA) compounded at a disproportionately higher rate than VA across integrated characters. Both hypotheses assume that each component of quantitative variation has an independent effect on heritability. However, VA and VR may also covary, in which case differences in heritability cannot be fully explained by the independent effects of elimination‐selection or compounded residual variation. We compared the central tendency of published behavioural heritabilities (mean=0.31, median=0.23) with morphological and life history data collected by 26 ). Average behavioural heritability was not significantly different from average life history heritability, but both were smaller than average morphological heritability. We cross‐classified behavioural traits to test whether variation in heritability was related to selection (dominance, domestic/wild) or variance compounding (integration level). There was a significant three‐way interaction between indices of selection and variance compounding, related to the absence of either effect at the highest integration level. At lower integration levels, high dominance variance indicated effects of selection. It was also indicated by the low CV A of domestic species. At the same time CV R increased disproportionately faster than CV A across integration levels, demonstrating variance compounding. However, neither CV R nor CV A had a predominant effect on heritability. The partial regression coefficients of CV R and CV A on heritability were similar and a path analysis indicated that their (positive) correlation was also necessary to explain variation in heritability. These results suggest that relationships between additive genetic and residual components of quantitative genetic variation can constrain their independent direct effects on behavioural heritability. 相似文献
14.
Phospholipases A 2 may exist in solution both as monomers and dimers, but enzymes that form strong dimers ( K
D
approximately 10 –9 M) have been found, thus far, only in venoms of the snake family Crotilidae. The complete amino acid sequences of a basic monomeric and an acidic dimeric phospholipase A 2 from Agkistrodon piscivorus piscivorus (American cotton-mouth water moccasin) venom have been determined by protein sequencing methods as part of a search for aspects of structure contributing to formation of stable dimers. Both the monomeric and dimeric phospholipases A 2 are highly homologous to the dimeric phospholipases A 2 from Crotalus atrox and Crotalus adamanteus venoms, and both have the seven residue carboxy-terminal extension characteristic of the crotalid and viperid enzymes. Thus, it is clear that the extension is not a prerequisite for dimerization. Studies to date have revealed two characteristic features of phosphilipases A 2 that exist in solution as strong dimers. One is the presence in the dimers of a Pro-Pro sequence at position 112 and 113 which just precedes the seven residue carboxy-terminal extension (residues 116–122). The other is a low isoelectric point; only the acidic phospholipases A 2 have been observed, thus far, to form stable dimers. These, alone or together, may be necessary, though not sufficient conditions for phospholipase A 2 dimer formation. Ideas regarding subunit interactions based upon crystallographic data are evaluated relative to the new sequence information on the monomeric and dimeric phospholipases A 2 from A. p. piscivorus venom. 相似文献
15.
A broad regional understanding of tropical forest leaf photosynthesis has long been a goal for tropical forest ecologists,
but it has remained elusive due to difficult canopy access and high species diversity. Here we develop an empirical model
to predict sunlit, light-saturated, tropical leaf photosynthesis using leaf and simulated canopy spectra. To develop this
model, we used partial least squares (PLS) analysis on three tropical forest datasets (159 species), two in Hawaii and one
at the biosphere 2 laboratory (B2L). For each species, we measured light-saturated photosynthesis ( A), light and CO 2 saturated photosynthesis ( A
max), respiration ( R), leaf transmittance and reflectance spectra (400–2,500 nm), leaf nitrogen, chlorophyll a and b, carotenoids, and leaf mass per area (LMA). The model best predicted A [ r
2
= 0.74, root mean square error (RMSE) = 2.9 μmol m −2 s −1)] followed by R ( r
2
= 0.48), and A
max ( r
2
= 0.47). We combined leaf reflectance and transmittance with a canopy radiative transfer model to simulate top-of-canopy
reflectance and found that canopy spectra are a better predictor of A (RMSE = 2.5 ± 0.07 μmol m −2 s −1) than are leaf spectra. The results indicate the potential for this technique to be used with high-fidelity imaging spectrometers
to remotely sense tropical forest canopy photosynthesis. 相似文献
16.
Two approaches to determine the fraction (μ) of mitochondrial respiration sustained during illumination by measuring CO 2 gas exchange are compared. In single leaves, the respiration rate in the light (`day respiration' rate R d) is determined as the ordinate of the intersection point of A–c i curves at various photon flux densities and compared with the CO 2 evolution rate in darkness (`night respiration' rate R n). Alternatively, using leaves with varying values of CO 2 compensation concentration (Γ), intracellular resistance (r i) and R n, an average number for μ can be derived from the linear regression between Γ and the product r iċR n. Both methods also result in a number c* for that intercellular CO 2 concentration at which net CO 2 uptake rate is equal to –R d. c* is an approximate value of the photocompensation point Γ* (Γ in the absence of mitochondrial respiration), which is related
to the CO 2/O 2 specificity factor of Rubisco S c/o. The presuppositions and limitations for application of both approaches are discussed. In leaves of Nicotiana tabacum, at 22 °C, single leaf measurements resulted in mean values of μ = 0.71 and c * = 34 μmol mol −1. At the photosynthetically active photon flux density of 960 μmol quanta m −2 s −1, nearly the same numbers were derived from the linear relationship between Γ and r iċR n. c* and R d determined by single leaf measurements varied between 31 and 41 μmol mol −1 and between 0.37 and 1.22 μmol m −2 s −1, respectively. A highly significant negative correlation between c* and R d was found. From the regression equation we obtained estimates for Γ* (39 μmol mol −1), S c/o (96.5 mol mol −1) and the mesophyll CO 2 transfer resistance (7.0 mol −1 m 2 s).
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
17.
Phospholipases A 2 may exist in solution both as monomers and dimers, but enzymes that form strong dimers ( K D approximately 10 ?9 M) have been found, thus far, only in venoms of the snake family Crotilidae. The complete amino acid sequences of a basic monomeric and an acidic dimeric phospholipase A 2 from Agkistrodon piscivorus piscivorus (American cotton-mouth water moccasin) venom have been determined by protein sequencing methods as part of a search for aspects of structure contributing to formation of stable dimers. Both the monomeric and dimeric phospholipases A 2 are highly homologous to the dimeric phospholipases A 2 from Crotalus atrox and Crotalus adamanteus venoms, and both have the seven residue carboxy-terminal extension characteristic of the crotalid and viperid enzymes. Thus, it is clear that the extension is not a prerequisite for dimerization. Studies to date have revealed two characteristic features of phosphilipases A 2 that exist in solution as strong dimers. One is the presence in the dimers of a Pro-Pro sequence at position 112 and 113 which just precedes the seven residue carboxy-terminal extension (residues 116–122). The other is a low isoelectric point; only the acidic phospholipases A 2 have been observed, thus far, to form stable dimers. These, alone or together, may be necessary, though not sufficient conditions for phospholipase A 2 dimer formation. Ideas regarding subunit interactions based upon crystallographic data are evaluated relative to the new sequence information on the monomeric and dimeric phospholipases A 2 from A. p. piscivorus venom. 相似文献
18.
Exosomes, small-sized extracellular vesicles, carry components of the purinergic pathway. The production by cells of exosomes carrying this pathway remains poorly understood. Here, we asked whether type 1, 2A, or 2B adenosine receptors (A1Rs, A2ARs, and A2BRs, respectively) expressed by producer cells are involved in regulating exosome production. Preglomerular vascular smooth muscle cells (PGVSMCs) were isolated from wildtype, A1R?/?, A2AR?/?, and A2BR?/? rats, and exosome production was quantified under normal or metabolic stress conditions. Exosome production was also measured in various cancer cells treated with pharmacologic agonists/antagonists of A1Rs, A2ARs, and A2BRs in the presence or absence of metabolic stress or cisplatin. Functional activity of exosomes was determined in Jurkat cell apoptosis assays. In PGVSMCs, A1R and A2AR constrained exosome production under normal conditions (p?=?0.0297; p?=?0.0409, respectively), and A1R, A2AR, and A2BR constrained exosome production under metabolic stress conditions. Exosome production from cancer cells was reduced (p?=?0.0028) by the selective A2AR agonist CGS 21680. These exosomes induced higher levels of Jurkat apoptosis than exosomes from untreated cells or cells treated with A1R and A2BR agonists (p?=?0.0474). The selective A2AR antagonist SCH 442416 stimulated exosome production under metabolic stress or cisplatin treatment, whereas the selective A2BR antagonist MRS 1754 reduced exosome production. Our findings indicate that A2ARs suppress exosome release in all cell types examined, whereas effects of A1Rs and A2BRs are dependent on cell type and conditions. Pharmacologic targeting of cancer with A2AR antagonists may inadvertently increase exosome production from tumor cells. 相似文献
19.
The adrenergic system is an essential regulator of neuronal, endocrine, cardiovascular, vegetative, and metabolic functions. The endogenous catecholamines epinephrine and norepinephrine activate G-protein-coupled receptors to transmit their signal across the plasma membrane. These adrenoceptors can be divided into three different groups: the α 1-receptors (α 1A, α 1B, α 1D), α 2-receptors (α 2A, α 2B, α 2C), and β-receptors (β 1, β 2, β 3). This review summarizes recent findings in the field of adrenoceptor signaling in neurons and includes a discussion of receptor-associated proteins, receptor dimerization, subcellular trafficking, and fluorescence optical methods for studying the kinetics of adrenergic signaling. Spatio-temporal imaging may become an important future tool for identifying the physiological significance of these complex signaling mechanisms in vivo. Gene-targeted mouse models carrying deletions in α 2-adrenoceptor have provided detailed insights into specific neuronal functions of the three α 2-receptor subtypes. 相似文献
20.
Adenosine is known to exert most of its physiological functions by acting as local modulator at four receptor subtypes named
A 1, A 2A, A 2B and A 3 (ARs). Principally as a result of the difficulty in identifying potent and selective agonists, the A 2B AR is the least extensively characterised of the adenosine receptors family. Despite these limitations, growing understanding
of the physiological meaning of this target indicates promising therapeutic perspectives for specific ligands. As A 2B AR signalling seems to be associated with pre/postconditioning cardioprotective and anti-inflammatory mechanisms, selective
agonists may represent a new therapeutic group for patients suffering from coronary artery disease. Herein we present an overview
of the recent advancements in identifying potent and selective A 2B AR agonists reported in scientific and patent literature. These compounds can be classified into adenosine-like and nonadenosine
ligands. Nucleoside-based agonists are the result of modifying adenosine by substitution at the N
6-, C 2-positions of the purine heterocycle and/or at the 5′-position of the ribose moiety or combinations of these substitutions.
Compounds 1-deoxy-1-{6-[ N′-(furan-2-carbonyl)-hydrazino]-9 H-purin-9-yl}-N-ethyl- β-D-ribofuranuronamide ( 19, hA 1
K
i = 1050 nM, hA 2A
K
i = 1550 nM, hA 2B EC 50 = 82 nM, hA 3
K
i > 5 μM) and its 2-chloro analogue 23 (hA 1
K
i = 3500 nM, hA 2A
K
i = 4950 nM, hA 2B EC 50 = 210 nM, hA 3
K
i > 5 μM) were confirmed to be potent and selective full agonists in a cyclic adenosine monophosphate (cAMP) functional assay
in Chinese hamster ovary (CHO) cells expressing hA 2B AR. Nonribose ligands are represented by conveniently substituted dicarbonitrilepyridines, among which 2-[6-amino-3,5-dicyano-4-[4-(cyclopropylmethoxy)phenyl]pyridin-2-ylsulfanyl]acetamide
( BAY-60–6583, hA 1, hA 2A, hA 3 EC 50 > 10 μM; hA 2B EC 50 = 3 nM) is currently under preclinical-phase investigation for treating coronary artery disorders and atherosclerosis. 相似文献
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