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121.
Ming-Jai Su PhD Wen-Pin Chen Tase-Yueh Lo Tian-Shung Wu 《Journal of biomedical science》1999,6(6):376-386
We investigated the electrophysiological effect and antiarrhythmic potential of cinnamophilin (Cinn), a thromboxane A2 antagonist isolated fromCinnamomum philippinense, on rat cardiac tissues. Action potential and ionic currents in single rat ventricular cells were examined by current clamp or voltage clamp in a whole-cell configuration. In 9 episodes of ischemia-reperfusion arrhythmia, 10 µM Cinn converted 6 of them to normal sinus rhythm. Cinn suppressed the maximal rate of rise of the action potential upstroke (Vmax) and prolonged the action potential duration at 50% repolarization (APD50). Voltage clamp study showed that the suppression of Vmax by Cinn was associated with an inhibition of sodium inward current (INa, IC50=10.0 ± 0.4 µM). At 30 µM, V1/2 for the steady-state inactivation curve of INa was shifted from –84.1 ± 0.2 to –93.0 ± 0.5 mV. Cinn also reduced calcium inward current (ICa) dose-dependently with an IC50 value of 9.5 ± 0.3 µM. Cinn (10 µM) reduced the ICa with a negative shift of V1/2 for the steady-state inactivation curve of ICa from –32.2 ± 0.3 to –50.7 ± 0.4 mV. The prolongation of APD50 was associated with an inhibition of the integral of potassium outward current with IC50 values between 4.8 and 7.1 µM. At 10 µM, Cinn reduced INa without a negative shift of its voltage-dependent steady-state inactivation curves. The inhibition of transient outward current (Ito) by Cinn (3–30 µM) was associated with an acceleration of its time constant of inactivation and negative shift of its potential-dependent steady-state inactivation curves. The equilibrium dissociation constant (Kd) of Cinn to inhibit open state Ito channels, as calculated from the time constant of developing block, was 18.3 µM. The time constant of recovery of Ito from inactivation state was unaffected by Cinn. The rate constant for the relief from the depolarization-dependent block of Ito was calculated to be 23.9 ms. As compared with its effect on Ito, Cinn exerted about half the potency to block INa and ICa. These results indicate that the inhibition of INa, ICa and Ito may contribute to the antiarrhythmic activity of Cinn against ischemia-reperfusion arrhythmia. 相似文献
122.
Studies of several gene knockout mice suggest an interesting association of a moderate T cell response with systemic autoimmune diseases. In addition, CD95 ligand (FasL) expression in some strains of these mice is impaired. Because FasL is critically involved in regulating peripheral tolerance, there may be a link between autoimmune diseases and a moderate T cell response that cannot activate the FasL gene. Here, we propose that there are two thresholds of T cell activation. When moderately stimulated, T cells can be activated to the low (1st) threshold, which permits the induction of CD40L, IL-2, IL-4, and other components that help the immune response. The high (2nd) activation threshold can only be achieved by a strong and concurrent stimulation through TCR and IL-2R. Once the high threshold is reached, FasL is produced to induce apoptosis of the activated T and B cells. In the absence of the FasL-mediated downregulation, the activated B cells become efficient antigen-presenting cells for self-antigens and excellent responders for T cell help. Such an exacerbating condition, induced by recurrent and moderate activation, favors the development of autoreactive T cells and autoantibody production. Evidence supporting this hypothesis and some predictions that can be tested are described. 相似文献
123.
Anna Sannino PhD Stefania Romeo PhD Maria Rosaria Scarfì Daniele Pinchera PhD Fulvio Schettino PhD Mario Alonzo PhD Mariateresa Allocca PhD Olga Zeni PhD 《Bioelectromagnetics》2024,45(3):97-109
This study aims to investigate the cellular effects of radiofrequency exposure, 1950 MHz, long-term evolution (LTE) signal, administered alone and in combination with mitomycin-C (MMC), a well-known cytotoxic agent. Chinese hamster lung fibroblast (V79) cells were exposed/sham exposed in a waveguide-based system under strictly controlled conditions of both electromagnetic and environmental parameters, at specific absorption rate (SAR) of 0.3 and 1.25 W/kg. Chromosomal damage (micronuclei formation), oxidative stress (reactive oxygen species [ROS] formation), and cell cycle progression were analyzed after exposure and coexposure. No differences between exposed samples and sham-controls were detected following radiofrequency exposure alone, for all the experimental conditions tested and biological endpoints investigated. When radiofrequency exposure was followed by MMC treatment, 3 h pre-exposure did not modify MMC-induced micronuclei. Pre-exposure of 20 h at 0.3 W/kg did not modify the number of micronuclei induced by MMC, while 1.25 W/kg resulted in a significant reduction of MMC-induced damage. Absence of effects was also detected when CW was used, at both SAR levels. MMC-induced ROS formation resulted significantly decreased at both SAR levels investigated, while cell proliferation and cell cycle progression were not affected by coexposures. The results here reported provide no evidence of direct effects of 1950 MHz, LTE signal. Moreover, they further support our previous findings on the capability of radiofrequency pre-exposure to induce protection from a subsequent toxic treatment, and the key role of the modulated signals and the experimental conditions adopted in eliciting the effect. 相似文献
124.
125.
Asad Ahmed 《PLoS genetics》2009,5(8)
Bacterial transposons are known to move to new genomic sites using either a replicative or a conservative mechanism. The behavior of transposon Tn5 is anomalous. In vitro studies indicate that it uses a conservative mechanism while in vivo results point to a replicative mechanism. To explain this anomaly, a model is presented in which the two mechanisms are not independent—as widely believed—but could represent alternate outcomes of a common transpositional pathway. 相似文献
126.
J.R. Alves A.C.M. Pereira M.C. Souza S.B. Costa A.S. Pinto A.L. Mattos-Guaraldi R. Hirata-Júnior A.C.P. Rosa L.M.B.O. Asad 《Journal of applied microbiology》2010,108(1):246-255
Aims: The aim of this study was to investigate the influence of low iron availability on biofilm formation and adherence to HEp-2 cells of enteroaggregative Escherichia coli (EAEC) strains isolated from diarrhoea cases.
Methods and Results: The ability of EAEC to form biofilm on a plastic surface was evaluated quantitatively and qualitatively after 3 and 18 h of incubation of strains with or without the iron chelator 2,2-dipyridyl. When submitted to low iron conditions, prototype EAEC 042 strain showed a decrease in biofilm formation. Conversely, an increase in biofilm formation was observed for the clinical EAEC strains cultured in restricted iron condition. Moreover, the reduction of iron concentration inhibited the aggregative adherence to HEp-2 cells of all EAEC strains tested. However, all effects promoted by iron chelation were suppressed by thiourea.
Conclusions: Low iron availability may modulate biofilm formation and adhesive properties of EAEC strains to HEp-2 cells.
Significance and Impact of the Study: The data obtained in this study provide useful insights on the influence of low iron conditions possibly associated with redox stress on the pathogenesis of EAEC strains. 相似文献
Methods and Results: The ability of EAEC to form biofilm on a plastic surface was evaluated quantitatively and qualitatively after 3 and 18 h of incubation of strains with or without the iron chelator 2,2-dipyridyl. When submitted to low iron conditions, prototype EAEC 042 strain showed a decrease in biofilm formation. Conversely, an increase in biofilm formation was observed for the clinical EAEC strains cultured in restricted iron condition. Moreover, the reduction of iron concentration inhibited the aggregative adherence to HEp-2 cells of all EAEC strains tested. However, all effects promoted by iron chelation were suppressed by thiourea.
Conclusions: Low iron availability may modulate biofilm formation and adhesive properties of EAEC strains to HEp-2 cells.
Significance and Impact of the Study: The data obtained in this study provide useful insights on the influence of low iron conditions possibly associated with redox stress on the pathogenesis of EAEC strains. 相似文献
127.
Beadell JS Ishtiaq F Covas R Melo M Warren BH Atkinson CT Bensch S Graves GR Jhala YV Peirce MA Rahmani AR Fonseca DM Fleischer RC 《Proceedings. Biological sciences / The Royal Society》2006,273(1604):2935-2944
The introduction of avian malaria (Plasmodium relictum) to Hawaii has provided a model system for studying the influence of exotic disease on naive host populations. Little is known, however, about the origin or the genetic variation of Hawaii's malaria and traditional classification methods have confounded attempts to place the parasite within a global ecological and evolutionary context. Using fragments of the parasite mitochondrial gene cytochrome b and the nuclear gene dihydrofolate reductase-thymidylate synthase obtained from a global survey of greater than 13000 avian samples, we show that Hawaii's avian malaria, which can cause high mortality and is a major limiting factor for many species of native passerines, represents just one of the numerous lineages composing the morphological parasite species. The single parasite lineage detected in Hawaii exhibits a broad host distribution worldwide and is dominant on several other remote oceanic islands, including Bermuda and Moorea, French Polynesia. The rarity of this lineage in the continental New World and the restriction of closely related lineages to the Old World suggest limitations to the transmission of reproductively isolated parasite groups within the morphological species. 相似文献
128.
Khan AU 《Bioinformation》2006,1(4):132
129.
130.
Asad S Torabi SF Fathi-Roudsari M Ghaemi N Khajeh K 《International journal of biological macromolecules》2011,48(4):566-570
Horseradish peroxidase (HRP) has attracted intense research interest due to its potential applications in biotechnological fields. However, inadequate stability under prevalent conditions such as elevated temperatures and H(2)O(2) exposure, has limited its industrial application. In this study, stability of HRP was investigated in the presence of different buffer systems (potassium phosphate and Tris-HCl) and additives. It was shown that the concentration of phosphate buffer severely affects enzyme thermostability in a way that in diluted potassium phosphate buffer (10mM) half-life (from 13 to 35 min at 80 °C) and T(m) (from 73 to 77.5 °C) increased significantly. Among additives tested, trehalose had the most thermostabilizing effect. Exploring the role of glycosylation in stabilizing effect of phosphate buffer, non-glycosylated recombinant HRP was also examined for its thermal and H(2)O(2) stability in both diluted and concentrated phosphate buffers. The recombinant enzyme was more thermally stable in diluted buffer in accordance to glycosylated HRP; but interestingly recombinant HRP showed higher H(2)O(2) tolerance in concentrated buffer. 相似文献