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1.
BARBARA RIEMER MCCREADIE SCOTT J. HOLLISTER 《Computer methods in biomechanics and biomedical engineering》2013,16(1):61-68
Direct cell sensing of tissue matrix strains is one possible signaling mechanism for mechanically mediated bone adaptation. We utilized homogenization theory lo estimate bone tissue matrix strains surrounding osteocytes using two sets of models. The first set of models estimated the strain levels surrounding the lacunae and canaliculi, taking into account variations in lamellar properties. The second set estimated strain levels in the osteocyte and the surrounding matrix for different cellular mechanical properties. The results showed that the strain levels found in and surrounding osteocytes, 1700 to 2700 microstrain (denoted as μe; 1 =.0001% strain), were significantly greater than the trabecular tissue level strains of [1325 μe, 287 μe, 87 μe] used for model input. Variation in lamellar properties did not affect strain levels, except at lamellar boundaries. Strain in and surrounding the osteocyte was not significantly affected by cellular stiffness ranging between 28 and 28,000 Pascals (Pa). Strain levels surrounding lacunae and canaliculi were approximately equivalent. 相似文献
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Osteocytes embedded in the matrix of bone are mechanosensory cells that translate strain into signals and regulate bone remodeling. Our previous studies using osteocyte-like MLO-Y4 cells have shown that fluid flow shear stress (FFSS) increases connexin (Cx) 43 protein expression, prostaglandin E2 (PGE2) release, and intercellular coupling, and PGE2 is an essential mediator between FFSS and gap junctions. However, the role of Cx43 in the release of PGE2 in response to FFSS is unknown. Here, the FFSS-loaded MLO-Y4 cells with no or few intercellular channels released significantly more PGE2 per cell than those cells at higher densities. Antisense Cx43 oligonucleotides and 18 β-glycyrrhetinic acid, a specific gap junction and hemichannel blocker, significantly reduced PGE2 release by FFSS at all cell densities tested, especially cells at the lowest density without gap junctions. FFSS, fluid flow-conditioned medium, and PGE2 increased the activity of dye uptake. Moreover, FFSS induced Cx43 to migrate to the surface of the cell; this surface expressed Cx43 developed resistance to Triton-X-100 solublization. Our results suggest that hemichannels formed by Cx43, instead of intercellular channels, are likely to play a predominant role in the release of intracellular PGE2 in response to FFSS. 相似文献
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《Cell communication & adhesion》2013,20(4-6):259-264
Osteocytes embedded in the matrix of bone are mechanosensory cells that translate strain into signals and regulate bone remodeling. Our previous studies using osteocyte-like MLO-Y4 cells have shown that fluid flow shear stress (FFSS) increases connexin (Cx) 43 protein expression, prostaglandin E2(PGE2) release, and intercellular coupling, and PGE2is an essential mediator between FFSS and gap junctions. However, the role of Cx43 in the release of PGE2in response to FFSS is unknown. Here, the FFSS-loaded MLO-Y4 cells with no or few intercellular channels released significantly more PGE2per cell than those cells at higher densities. Antisense Cx43 oligonucleotides and 18 β-glycyrrhetinic acid, a specific gap junction and hemichannel blocker, significantly reduced PGE2release by FFSS at all cell densities tested, especially cells at the lowest density without gap junctions. FFSS, fluid flow-conditioned medium, and PGE2increased the activity of dye uptake. Moreover, FFSS induced Cx43 to migrate to the surface of the cell; this surface expressed Cx43 developed resistance to Triton-X-100 solublization. Our results suggest that hemichannels formed by Cx43, instead of intercellular channels, are likely to play a predominant role in the release of intracellular PGE2in response to FFSS. 相似文献
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Transformation of Low Concentrations of 3-Chlorobenzoate by Pseudomonas sp. Strain B13: Kinetics and Residual Concentrations 总被引:4,自引:1,他引:4 下载免费PDF全文
The transformation of 3-chlorobenzoate (3CB) and acetate at initial concentrations in the wide range of 10 nM to 16 mM was studied in batch experiments with Pseudomonas sp. strain B13. Transformation rates of 3CB at millimolar concentrations could be described by Michaelis-Menten kinetics (K(infm), 0.13 mM; V(infmax), 24 nmol (middot) mg of protein(sup-1) (middot) min(sup-1)). Experiments with nanomolar and low micromolar concentrations of 3CB indicated the possible existence of two different transformation systems for 3CB. The first transformation system operated above 1 (mu)M 3CB, with an apparent threshold concentration of 0.50 (plusmn) 0.11 (mu)M. A second transformation system operated below 1 (mu)M 3CB and showed first-order kinetics (rate constant, 0.076 liter (middot) g of protein(sup-1) (middot) min(sup-1)), with no threshold concentration in the nanomolar range. A residual substrate concentration, as has been reported for some other Pseudomonas strains, could not be detected for 3CB (detection limit, 1.0 nM) in batch incubations with Pseudomonas sp. strain B13. The addition of various concentrations of acetate as a second, easily degradable substrate neither affected the transformation kinetics of 3CB nor induced a detectable residual substrate concentration. Acetate alone also showed no residual concentration (detection limit, 0.5 nM). The results presented indicate that the concentration limits for substrate conversion obtained by extrapolation from kinetic data at higher substrate concentrations may underestimate the true conversion capacity of a microbial culture. 相似文献
6.
Concentrations of 3,4-Dihydroxyphenylalanine and Catecholamines and Metabolites in Brain in an Anhepatic Model of Hepatic Encephalopathy 总被引:2,自引:0,他引:2
Robert Hadesman Russell H. Wiesner V. L. W. Go Gertrude M. Tyce 《Journal of neurochemistry》1995,65(3):1166-1175
Abstract: Alterations in the catecholaminergic neurotransmitter systems have been shown to occur in hepatic failure and may contribute to development of hepatic encephalopathy. In the present study we used the rat after complete hepatectomy as a model for study of changes that occur in brain in acute liver failure. We attempted to identify processes in the synthesis, storage, and metabolism of catecholamine neurotransmitters that might be changed during liver failure by measuring levels of, together with those of norepinephrine and dopamine, the precursor (3,4-dihydroxyphenylalanine) and the neuronal metabolites of dopamine and norepinephrine (3,4-dihydroxyphenylacetic acid and 3,4-dihydroxyphenylglycol, respectively) in different regions of brains of control rats and of rats after hepatectomy. We found that in most brain regions of hepatectomized rats there were increases in the concentration of 3,4-dihydroxyphenylalanine or of dopamine but decreases in the concentrations of norepinephrine or of 3,4-dihydroxyphenylglycol. The particulate/supernatant ratios of catecholamines are indices of retention of neurotransmitters in storage sites. These ratios were not different in brain regions between control rats and hepatectomized rats, suggesting that vesicular retention of catecholamines in brain was not impaired after hepatectomy. The data suggest that inhibition of dopamine-β-hydroxylase might be a characteristic of hepatic failure. 相似文献
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Benhua Zeng Guiqing Li Jing Yuan Wenxia Li Huan Tang Hong Wei 《Current microbiology》2013,67(3):313-321
The establishment of human flora-associated animal models allows the in vivo manipulation of host, microbial, and environmental parameters to influence the gut microbial community. However, it is difficult to simulate infant gut microbiota in germ-free animals because of the variation and dynamic state of infant microbial communities. In this study, the effects of age and strain on intestinal microbiota were observed in an infant human flora-associated (IHFA) mouse model. To establish an IHFA model, postnatal day (PND) 1 germ-free mice (Kunming, n = 10; BALB/c, n = 10) were infected with feces from a breast-fed infant. Microbiota in the feces of BALB/c mice (at PND 7, 14, and 21), and Kunming mice (at PND 14) were analyzed by PCR-denaturing gradient gel electrophoresis. Bifidobacteria and lactobacilli levels in the feces of BALB/c and Kunming mice (PND 7/14/21) were detected by quantitative real-time PCR. The Dice similarity coefficient (Cs) for the fecal microbiota of IHFA mice in comparison with the HD donor sample was higher for BALB/c mice than for Kunming mice (P < 0.05). In addition, the DCs at PND 7 were lower than those at PND 14 and PND 21 in both mouse strains (P < 0.05). The Bifidobacteria and Lactobacillus species colonizing the BALB/c mice were similar to those in the Kunming mice (at PND 7/14/21). The bifidobacteria counts increased with age in both mouse strains, whereas the lactobacilli counts decreased with age in both strains. These results suggest that both age and strain influence microbiota patterns in the IHFA mouse model. 相似文献
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Kolpakov V. G. Kulikov A. V. Alekhina T. A. Chuguy V. F. Petrenko O. I. Barykina N. N. 《Russian Journal of Genetics》2004,40(6):672-678
The utility of incomplete genetic animal models of human diseases, in particular, psychoses, is discussed. The GC rat strain selected for predisposition to cataleptic reactions is described. It is shown that in many of their characteristics, GC rats are similar to schizophrenic and depressive patients. A possibility that akinetic catatonic states and depressions, hyperkinetic catatonic states and mania share common mechanisms is discussed. It is hypothesized that the GC strain may be an incomplete model of the common genetic and pathogenetic core of schizophrenic substuporous states and depression, which suggests the importance of returning to the issue of the unitary psychosis (Einheitpsychosis). 相似文献
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Computer Simulation of Clostridium botulinum Strain 56A Behavior at Low Spore Concentrations 下载免费PDF全文
It is generally assumed that spore behavior is independent of spore concentration, but recently published mathematical models indicate that this is not the case. A Monte Carlo simulation was employed in this study to further examine the independence assumption by evaluating the inherent variance in spore germination data. All simulations were carried out with @Risk software. A total of 500 to 4,000 iterations were needed for each simulation to reach convergence. Lag time and doubling time from a higher inoculum concentration were used to simulate the time to detection (TTD) at a lower inoculum concentration under otherwise identical environmental conditions. The point summaries of the simulated and observed TTDs were recorded for the 26 simulations, with kinetic data at the target inoculum concentration. The ratios of the median (Rm = medianobs/mediansim) and 90% range (Rr = 90% rangeobs/90% rangesim) were calculated. Most Rm and Rr values were greater than one, indicating that the simulated TTDs were smaller and more homogeneous than the observed ones. Rr values departed farther from one than Rm values. Ratios obtained when simulating 1 spore with 10,000 spores deviated the farthest from one. Neither ratio was significantly different from the other when simulating 1 spore with 100 spores or simulating 100 spores with 10,000 spores. When kinetic data were not available, the percent positive observed at the 95th percentile of the simulated TTDs was obtained. These simulation results confirmed that the assumption of independence between spores is not valid. 相似文献
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Kristen L. Jurcic Smith Divey Saini Svetoslav Bardarov Michelle Larsen Richard Frothingham Neel R. Gandhi William R. Jacobs Jr. A. Willem Sturm Sunhee Lee 《PloS one》2014,9(4)
Bacterial drug resistance is often associated with a fitness cost. Large outbreaks of multidrug-resistant (MDR) and extensively drug-resistant (XDR) TB have been described that predominately affect persons with HIV infection. We obtained four closely-related Mycobacterium tuberculosis strains (genotype F15/LAM4/KZN) from an outbreak in KwaZulu-Natal (KZN), South Africa, including drug-sensitive, MDR, and XDR clinical isolates. We compared the virulence of these strains in a murine model of aerosol M. tuberculosis infection for four phenotypes: (1) competitive in vivo growth in lung and spleen, (2) non-competitive in vivo growth in lung and spleen, (3) murine survival time, and (4) lung pathology. When mixtures of sensitive, MDR, and XDR KZN strains were aerosolized (competitive model), lung CFUs were similar at 60 days after infection, and spleen CFUs were ordered as follows: sensitive > MDR > XDR. When individual strains were aerosolized (non-competitive model), modest differences in lung and spleen CFUs were observed with the same ordering. C57BL/6, C3H/FeJ, and SCID mice all survived longer after infection with MDR as compared to sensitive strains. SCID mice infected with an XDR strain survived longer than those infected with MDR or sensitive strains. Lung pathology was reduced after XDR TB infection compared to sensitive or MDR TB infection. In summary, increasing degrees of drug resistance were associated with decreasing murine virulence in this collection of KZN strains as measured by all four virulence phenotypes. The predominance of HIV-infected patients in MDR and XDR TB outbreaks may be explained by decreased virulence of these strains in humans. 相似文献
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J. B. Litzenberger P. Tummala C. R. Jacobs 《Molecular & cellular biomechanics : MCB》2006,3(4):219-220
This article has no abstract. 相似文献
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Vakhtang V. Dzhavakhiya Tatiana M. Voinova Elena V. Glagoleva Dmitry V. Petukhov Alexander I. Ovchinnikov Maksim I. Kartashov Boris B. Kuznetsov Konstantin G. Skryabin 《Indian journal of microbiology》2015,55(4):440-446
Pravastatin is one of the most popular cholesterol-lowering drugs. Its industrial production represents a two-stage process including the microbial production of compactin and its further biocatalytic conversion to pravastatin. To increase a conversion rate, a higher compactin content in fermentation medium should be used; however, high compactin concentrations inhibit microbial growth. Therefore, the improvement of the compactin resistance of a producer still remains a relevant problem. A multi-step random UV mutagenesis of a Streptomyces xanthochromogenes strain RIA 1098 and the further selection of high-yield compactin-resistant mutants have resulted in a highly productive compactin-resistant strain S 33-1. After the fermentation medium improvement, the maximum bioconversion rate of this strain has reached 91 % at the daily compactin dose equal to 1 g/L and still remained high (83 %) even at the doubled dose (2 g/L). A 1-year study of the mutant strain stability has proved a stable inheritance of its characteristics that provides this strain to be very promising for the pravastatin-producing industry.
Electronic supplementary material
The online version of this article (doi:10.1007/s12088-015-0537-5) contains supplementary material, which is available to authorized users. 相似文献15.
禽呼肠孤病毒变异株的分离鉴定 总被引:5,自引:0,他引:5
从病鸡肝分离到一株病毒,经电镜检查、理化特性分析、核酸电泳和中和试验等证明它为禽呼肠孤病毒(ARV)。该病毒只在鸡胚肝细胞(CELi)上产生细胞病变(CPE),在鸡胚成纤维细胞(CEF)和V_(ero)细胞上不增殖,它对热无敏感,Mg ̄(2+)不能增强其对热的稳定性,其基因组中的4个小节段的迁移率与ARVFDO和S_(1133)株明显不同,表明它是不同于FDO和S_(1133)的ARV变异株。 相似文献
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Lactose and Sulfide Reactions of an Aberrant Salmonella Strain 总被引:2,自引:0,他引:2
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Thomas J. Lauterio Michael J. Davies Mark DeAngelo Michael Peyser James Lee 《Obesity (Silver Spring, Md.)》1999,7(5):498-505
LAUTERIO, THOMAS J., MICHAEL J. DAVIES, MARK DEANGELO, MICHAEL PEYSER, AND JAMES LEE. Neuropeptide Y expression and endogenous leptin concentrations in a dietary model of obesity. Obes Res. Objective: To determine how leptin concentrations and neuropeptide (NPY) are regulated in a model of dietary obesity in relation to relative growth (RG) and relative food consumption (RFC). Research Methods and Procedures: Sprague—Dawley rats were fed a moderately high-fat diet for 14 weeks over which time animals diverged into obesity-prone (OP) and obesity-resistant (OR) populations. RG rates and RFC were calculated weekly. Following the study, an adiposity index was calculated and arcuate nucleus (ARC) NPY expression was determined by in situ hybridization (ISH) or ribonuclease protection (RPA) assays. Results: Body weights were greater in OP rats after 2 weeks on the diet compared to OR rats and remained different throughout the study. RG and RFC were greater in OP rats compared to OR rats only during the first 2 weeks of the study. Leptin concentrations rose in both groups during the experiment, but the increase was greater in OP rats than in OR rats. Insulin changes paralleled those for leptin. ARC NPY mRNA expression was not different between OP and OR rats as measured by ISH and RPA. Discussion: Although NPY expression has been reported to be different initially in OP and OR rats, this difference dissipates following divergence of body weight. RFC and RG data suggest the initial NPY elevation may contribute to increased weight gain of OP rats during the first 2 weeks of the diet. Higher relative leptin concentrations in OP rats may be necessary to normalize differences in adiposity and apparent leptin and insulin resistance of OP rats. 相似文献
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Hena R. Ramay 《Biophysical journal》2009,97(2):443-452
Several experiments on permeabilized heart muscle fibers suggest the existence of diffusion restrictions grouping mitochondria and surrounding ATPases. The specific causes of these restrictions are not known, but intracellular structures are speculated to act as diffusion barriers. In this work, we assume that diffusion restrictions are induced by sarcoplasmic reticulum (SR), cytoskeleton proteins localized near SR, and crowding of cytosolic proteins. The aim of this work was to test whether such localization of diffusion restrictions would be consistent with the available experimental data and evaluate the extent of the restrictions. For that, a three-dimensional finite-element model was composed with the geometry based on mitochondrial and SR structural organization. Diffusion restrictions induced by SR and cytoskeleton proteins were varied with other model parameters to fit the set of experimental data obtained on permeabilized rat heart muscle fibers. There are many sets of model parameters that were able to reproduce all experiments considered in this work. However, in all the sets, <5-6% of the surface formed by SR and associated cytoskeleton proteins is permeable to metabolites. Such a low level of permeability indicates that the proteins should play a dominant part in formation of the diffusion restrictions. 相似文献
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Multiphasic Kinetics of Transformation of 1,2,4-Trichlorobenzene at Nano- and Micromolar Concentrations by Burkholderia sp. Strain PS14 总被引:2,自引:0,他引:2 下载免费PDF全文
Peter Rapp 《Applied microbiology》2001,67(8):3496-3500
The transformation of 1,2,4-trichlorobenzene (1,2,4-TCB) at initial concentrations in nano- and micromolar ranges was studied in batch experiments with Burkholderia sp. strain PS14. 1,2,4-TCB was metabolized from nano- and micromolar concentrations to below its detection limit of 0.5 nM. At low initial 1,2,4-TCB concentrations, a first-order relationship between specific transformation rate and substrate concentration was observed with a specific affinity (a0A) of 0.32 liter · mg (dry weight)−1 · h−1 followed by a second one at higher concentrations with an aoA of 0.77 liter · mg (dry weight)−1 · h−1. This transition from the first-order kinetics at low initial 1,2,4-TCB concentrations to the second first-order kinetics at higher 1,2,4-TCB concentrations was shifted towards higher initial 1,2,4-TCB concentrations with increasing cell mass. At high initial concentrations of 1,2,4-TCB, a maximal transformation rate of approximately 37 nmol · min−1 · mg (dry weight)−1 was measured, irrespective of the cell concentration. 相似文献