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1.
Duchenne muscular dystrophy (DMD) is a lethal X-inherited disease caused by dystrophin deficiency. Besides the relatively well characterized skeletal muscle degenerative processes, DMD is also associated with a dilated cardiomyopathy that leads to progressive heart failure at the end of the second decade. The aim of the present study was to characterize the diastolic Ca2+ concentration ([Ca2+]d) and diastolic Na+ concentration ([Na+]d) abnormalities in cardiomyocytes isolated from 3-, 6-, 9-, and 12-month old mdx mice using ion-selective microelectrodes. In addition, the contributions of gadolinium (Gd3+)-sensitive Ca2+ entry and inositol triphosphate (IP3) signaling pathways in abnormal [Ca2+]d and [Na+]d were investigated. Our results showed an age-dependent increase in both [Ca2+]d and [Na+]d in dystrophic cardiomyocytes compared to those isolated from age-matched wt mice. Gd3+ treatment significantly reduced both [Ca2+]d and [Na+]d at all ages. In addition, blockade of the IP3-pathway with either U-73122 or xestospongin C significantly reduced ion concentrations in dystrophic cardiomyocytes. Co-treatment with U-73122 and Gd3+ normalized both [Ca2+]d and [Na+]d at all ages in dystrophic cardiomyocytes. These data showed that loss of dystrophin in mdx cardiomyocytes produced an age-dependent intracellular Ca2+ and Na+ overload mediated at least in part by enhanced Ca2+ entry through Gd3+ sensitive transient receptor potential channels (TRPC), and by IP3 receptors.  相似文献   
2.
Unique species of ceramide (Cer) with very-long-chain polyunsaturated fatty acid (VLCPUFA), mainly 28–32 carbon atoms, 4–5 double bonds, in nonhydroxy and 2-hydroxy forms (n-V Cer and h-V Cer, respectively), are generated in rat spermatozoa from the corresponding sphingomyelins during the acrosomal reaction. The aim of this study was to determine the properties of these sperm-distinctive ceramides in Langmuir monolayers. Individual Cer species were isolated by HPLC and subjected to analysis of surface pressure, surface potential, and Brewster angle microscopy (BAM) as a function of molecular packing. In comparison with known species of Cer, n-V Cer and h-V Cer species showed much larger mean molecular areas and increased molecular dipole moments in liquid expanded phases, which suggest bending and partial hydration of the double bonded portion of the VLCPUFA. The presence of the 2-hydoxyl group induced a closer molecular packing in h-V Cer than in their chain-matched n-V Cer. In addition, all these Cer species showed liquid-expanded to liquid-condensed transitions at room temperature. Existence of domain segregation was confirmed by BAM. Additionally, thermodynamic analysis suggests a phase transition close to the physiological temperature for VLCPUFA-Cers if organized as bulk dispersions.  相似文献   
3.
Mitochondrial hexokinase (HK) and creatine kinase (CK) known to form complexes with a voltage dependent anion channel (VDAC) have been reported to increase cell death resistance under hypoxia/anoxia. In this work we propose a new, non-Mitchell mechanism of generation of the inner and outer membrane potentials at anaerobic conditions. The driving force is provided by the Gibbs free energy of the HK and CK reactions associated with the VDAC–HK and the ANT (adenine nucleotide translocator)–CK–VDAC complexes, respectively, both functioning as voltage generators. In the absence of oxygen, the cytosolic creatine phosphate can be directly used by the ANT–CK–VDAC contact sites to produce ATP from ADP in the mitochondrial matrix. After that, ATP released through the fraction of unbound ANTs in exchange for ADP is used in the mitochondrial intermembrane space by the outer membrane VDAC–HK electrogenic complexes to convert cytosolic glucose into glucose-6-phosphate. A simple computational model based on the application of Ohm's law to an equivalent electrical circuit showed a possibility of generation of the inner membrane potential up to − 160 mV, under certain conditions, and of relatively high outer membrane potential without wasting of ATP that normally leads to cell death. The calculated membrane potentials depended on the restriction of ATP/ADP diffusion in narrow cristae and through the cristae junctions. We suggest that high inner membrane potential and calcium extrusion from the mitochondrial intermembrane space by generated positive outer membrane potential prevent mitochondrial permeability transition, thus allowing the maintenance of mitochondrial integrity and cell survival in the absence of oxygen.  相似文献   
4.
选取我国东北、西南、西北及中北部地区的10个典型湖泊,调查了表层沉积物生物硅含量变化情况,并通过区域对比分析了生物硅含量变化的原因,寻找我国湖泊生物硅变化的空间规律。结果表明,西北及中北部地区湖泊生物硅含量平均值整体低于东北和西南地区湖泊,可能是由于西北及中北部地区较低的温度和较少的降水量导致硅藻生长受限,从而造成生物硅含量偏低。东北湖泊与西南湖泊生物硅含量相对较高,但其形成原因不同。东北2个湖泊均靠近人类聚居区,属富营养型湖泊,虽然东北地区年均温较低,但充足的营养盐为硅藻生长提供了必要因素。而西南地区湖泊大多为中贫营养型湖泊,其生物硅含量整体较高可能主要归因于较高的温度和较多的降水。  相似文献   
5.
Current challenges to global food security require sustainable intensification of agriculture through initiatives that include more efficient use of nitrogen (N), increased protein self‐sufficiency through homegrown crops, and reduced N losses to the environment. Such challenges were addressed in a continental‐scale field experiment conducted over 3 years, in which the amount of total nitrogen yield (Ntot) and the gain of N yield in mixtures as compared to grass monocultures (Ngainmix) was quantified from four‐species grass–legume stands with greatly varying legume proportions. Stands consisted of monocultures and mixtures of two N2‐fixing legumes and two nonfixing grasses. The amount of Ntot of mixtures was significantly greater (P ≤ 0.05) than that of grass monocultures at the majority of evaluated sites in all 3 years. Ntot and thus Ngainmix increased with increasing legume proportion up to one‐third of legumes. With higher legume percentages, Ntot and Ngainmix did not continue to increase. Thus, across sites and years, mixtures with one‐third proportion of legumes attained ~95% of the maximum Ntot acquired by any stand and had 57% higher Ntot than grass monocultures. Realized legume proportion in stands and the relative N gain in mixture (Ngainmix/Ntot in mixture) were most severely impaired by minimum site temperature (R = 0.70, P = 0.003 for legume proportion; R = 0.64, P = 0.010 for Ngainmix/Ntot in mixture). Nevertheless, the relative N gain in mixture was not correlated to site productivity (P = 0.500), suggesting that, within climatic restrictions, balanced grass–legume mixtures can benefit from comparable relative gains in N yield across largely differing productivity levels. We conclude that the use of grass–legume mixtures can substantially contribute to resource‐efficient agricultural grassland systems over a wide range of productivity levels, implying important savings in N fertilizers and thus greenhouse gas emissions and a considerable potential for climate change mitigation.  相似文献   
6.
对采自广西、云南和广东的美花石斛(Dendrobium loddigesii Rolfe)野生植株根、茎和叶内的内生细菌进行分离并测定其促生特性,采用扩增核糖体DNA限制性酶切分析(ARDRA)与UPGMA聚类分析相结合的方法对内生细菌菌株进行分类并确定优势属;在此基础上,对具有解磷、解钾和产生长素能力的菌株进行促生潜力评价。结果显示:从不同产地美花石斛植株不同部位共分离得到67株内生细菌菌株,其分布呈现出组织与地区的特异性;其中,来源于广西的植株中菌株数量最多(42株),分离自茎的菌株数量最多(34株)。67株内生细菌菌株可分为31个ARDRA簇,经16S rDNA序列比对鉴定为12个属,包括假单胞菌属(Pseudomonas)、微杆菌属(Microbacterium)、肠杆菌属(Enterobacter)、芽孢杆菌属(Bacillus)、鞘氨醇单胞菌属(Sphingomonas)、葡萄球菌属(Staphylococcus)、嗜冷杆菌属(Psychrobacter)、短波单胞菌属(Brevundimonas)、涅斯捷连科氏菌属(Nesterenkonia)、副球菌属(Paracoccus)、泛菌属(Pantoea)和沙雷氏菌属(Serratia),其中芽孢杆菌属、微杆菌属和肠杆菌属为优势属;来源于广西的植株中内生细菌的丰度与多样性均高于其他两地。在67株内生细菌菌株中,有30株菌株具有解无机磷和解有机磷的双重能力、22株具有解钾能力、24株具有产生长素能力,其中仅8株菌株兼具3种促生能力。组培实验结果显示:在培养基中接种1×106CFU·mL-1芽孢杆菌DLB20菌株,对株高2~3 cm和3~4 cm的美花石斛试管苗生长有促进作用,且更有利于株高3~4 cm试管苗的生根,表明具有解磷、解钾和产生长素能力的菌株对美花石斛试管苗有一定的促生潜力。  相似文献   
7.
8.
CO2 exchange between the atmosphere and soil algal crusts of the Trachypogon savannas of the Orinoco Llanos has been analyzed using an open gas exchange system. These savannas encompass a wide range of physiognomic types, from herbaceous communities to savanna woodlands. A maximum CO2 flux of 0.207 mg m-2 s-1 was measured in the crusts of the Guanipa savannas, while in the other examined crusts (0.035–0.105 mg m-2 s-1) the flux was similar to values reported for terrestrial algae. The CO2 flux data were statistically fitted to the photosynthetically active radiation by a logarithmic relationship, and the photosynthetic efficiencies of the crusts were compared. The activation energy calculated for the CO2 fixation indicates that limitations by diffusion and photochemical processes were excluded in the Guanipa crusts (above 12 kcal mole-1), whereas they were evident in the other crust studied. An optimum CO2 incorporation as a function of the crust water potential was established and carbon gain strategies were proposed on the basis of the results and characteristics of the habitats.  相似文献   
9.
The 3-dimensional optimization of the electrostatic interactions between the charged amino acid residues was studied by Monte Carlo simulations on an extended representative set of 141 protein structures with known atomic coordinates. The proteins were classified by different functional and structural criteria, and the optimization of the electrostatic interactions was analyzed. The optimization parameters were obtained by comparison of the contribution of charge-charge interactions to the free energy of the native protein structures and for a large number of randomly distributed charge constellations obtained by the Monte Carlo technique. On the basis of the results obtained, one can conclude that the charge-charge interactions are better optimized in the enzymes than in the proteins without enzymatic functions. Proteins that belong to the mixed αβ folding type are electrostatically better optimized than pure α-helical or β-strand structures. Proteins that are stabilized by disulfide bonds show a lower degree of electrostatic optimization. The electrostatic interactions in a native protein are effectively optimized by rejection of the conformers that lead to repulsive charge-charge interactions. Particularly, the rejection of the repulsive contacts seems to be a major goal in the protein folding process. The dependence of the optimization parameters on the choice of the potential function was tested. The majority of the potential functions gave practically identical results.  相似文献   
10.
Electrical impedance measurements made on white spruce, Picea glauca (Moench) Voss, stems were related to shoot free sugar contents and to osmotic, turgor and water potential. During seasonal dormancy induction, there were commensurate increases in free sugar contents, osmotic potential at full turgor and impedance which resulted in linear relationships among these variables. When measured over the course of laboratory drying, impedance increased curvilinearly with decreasing relative water content. There was a linear increase in impedance with decreasing water potential, with a break point coincident with the turgor loss point, possibly attributed to disruption to current flow through broken plasmodesmatal connections between adjacent cells. This technique offers a non-destructive method to measure tissue free sugar content, and therefore, short- and long-term shifts in parameters historically derived from pressure-volume analysis.  相似文献   
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