Effects of taurine depletion on intrinsic contractility of rat ventricular papillary muscles

Contractile parameters in Krebs-Henseleit media containing various calcium concentrations were compared in left ventricular papillary muscles of two groups of rats: control and taurine depleted. All tests were carried out with the muscles at initial length, Lmax, the length that produced maximal active tension. From measurements of after- and un-loaded contractions, the velocity-tension curves and the derived maximum velocity of shortening were not different between the groups. Time to peak shortening and extent of shortening were not altered, while relaxation times and contraction duration were significantly prolonged for taurine-depleted muscles. Peak isometric tension and its rate of development were significantly reduced in taurine-depleted muscles compared with controls. Postrest (3 min) stimuli and paired stimuli (200-ms interval) evoked similar potentiated contractile responses in both groups, such that the ratio of their peak tensions remained unchanged. For taurine-depleted muscles the force-frequency relationship (a negative staircase) was parallel to, but lower than, control. These experiments suggest that taurine deficiency leads to reductions in action potential triggered calcium release from internal stores, and deficits in calcium sequestration. This may result from disfacilitation of calcium binding to the sarcoplasmic reticulum and other storage sites during taurine deficiency.     

Comparison of Photoacclimation in Twelve Freshwater Photoautotrophs (Chlorophyte,Bacillaryophyte, Cryptophyte and Cyanophyte) Isolated from a Natural Community

Different representative of algae and cyanobacteria were isolated from a freshwater habitat and cultivated in laboratory to compare their photoacclimation capacity when exposed to a wide range of light intensity and to understand if this factor may modify natural community dominance. All species successfully acclimated to all light intensities and the response of phytoplankton to increased light intensity was similar and included a decrease of most photosynthetic pigments accompanied by an increase in photoprotective pigment content relative to Chl a. Most species also decreased their light absorption efficiency on a biovolume basis. This decrease not only resulted in a lower fraction of energy absorbed by the cell, but also to a lower transfer of energy to PSII and PSI. Furthermore, energy funnelled to PSII or PSI was also rearranged in favour of PSII. High light acclimated organisms also corresponded to high non-photochemical quenching and photosynthetic electron transport reduction state and to a low Φ''_M. Thus photoacclimation processes work toward reducing the excitation pressure in high light environment through a reduction of light absorption efficiency, but also by lowering conversion efficiency. Interestingly, all species of our study followed that tendency despite being of different functional groups (colonial, flagellated, different sizes) and of different phylogeny demonstrating the great plasticity and adaptation ability of freshwater phytoplankton to their light environment. These adjustments may explain the decoupling between growth rate and photosynthesis observed above photosynthesis light saturation point for all species. Even if some species did reach higher growth rate in our conditions and thus, should dominate in natural environment with respect to light intensity, we cannot exclude that other environmental factors also influence the population dynamic and make the outcome harder to predict.     

Bicarbonate infusion and pH clamp moderately reduce hyperventilation during ramp exercise in humans.

To test the hypothesis that the decrease in plasma pH contributes to the hyperventilation observed in humans in response to exercise at high workloads, five healthy male subjects performed a ramp exercise [maximal workload: 352 W (SD 35)] in a control situation and when arterialized plasma pH was maintained at the resting level (pH clamp) by intravenous infusion of sodium bicarbonate [129 mmol (SD 23), beginning at 59% maximal workload (SD 5)]. Bicarbonate infusion did not modify O(2) consumption (Vo(2)) but significantly (P < 0.05) increased arterial Pco(2), plasma bicarbonate concentration, and respiratory exchange ratio (P < 0.05). At the three highest workloads, pulmonary ventilation (Ve) and Ve/Vo(2) were approximately 5-10% lower (P < 0.05) when bicarbonate was infused than in the control situation, and hyperventilation was reduced by 15-30%. These data suggest that the decrease in plasma pH is one of the factors that contribute to the hyperventilation observed at high workloads.     

Peroxiredoxin II Regulates Effector and Secondary Memory CD8+ T Cell Responses

Reactive oxygen intermediates (ROI) generated in response to receptor stimulation play an important role in cellular responses. However, the effect of increased H₂O₂ on an antigen-specific CD8⁺ T cell response was unknown. Following T cell receptor (TCR) stimulation, the expression and oxidation of peroxiredoxin II (PrdxII), a critical antioxidant enzyme, increased in CD8⁺ T cells. Deletion of PrdxII increased ROI, S phase entry, division, and death during in vitro division. During primary acute viral and bacterial infection, the number of effector CD8⁺ T cells in PrdxII-deficient mice was increased, while the number of memory cells were similar to those of the wild-type cells. Adoptive transfer of P14 TCR transgenic cells demonstrated that the increased expansion of effector cells was T cell autonomous. After rechallenge, effector CD8⁺ T cells in mutant animals were more skewed to memory phenotype than cells from wild-type mice, resulting in a larger secondary memory CD8⁺ T cell pool. During chronic viral infection, increased antigen-specific CD8⁺ T cells accumulated in the spleens of PrdxII mutant mice, causing mortality. These results demonstrate that PrdxII controls effector CD8⁺ T cell expansion, secondary memory generation, and immunopathology.     

Comparative studies on the photosynthetic responses of three freshwater phytoplankton species to temperature and light regimes

The photosynthetic responses of Microcystis aeruginosa, Scenedesmus obliquus, and Cyclotella meneghiniana to temperature and light regimes were investigated. M. aeruginosa had a higher specific growth rate at 30°C than at 14 and 20°C. Its specific growth rate was the maximum among the three species at 30°C. This suggests that M. aeruginosa could predominate in a water body having high temperature. When exposed to high light, M. aeruginosa showed lower maximal photosystem II (PSII) quantum yield (Φ_M), operational PSII quantum yield ( $ \Phi_{\text{M}}^{\prime } $ ), and active reaction centers per excited cross section (RC/CS_m) than S. obliquus and C. meneghiniana. Moreover, after 2?h low light recovery at 14°C and 20°C, the recovery of Φ_M, $ \Phi_{\text{M}}^{\prime } $ and RC/CS_m in M. aeruginosa were less than the other two species. This indicates that the capacity of high light adaptation of M. aeruginosa is the lowest among the studied species at 14–20°C. When exposed to high light, C. meneghiniana had higher Φ_M and $ \Phi_{\text{M}}^{\prime } $ lost and induced higher nonphotochemical quenching at 14–20°C. This suggests that C. meneghiniana developed a higher resistance to high light under low growth temperatures. M. aeruginosa showed the lowest light compensation point among these three species, which indicates that it could utilize low light more efficiently than the other two species. Cyclic electron flow around PSII may play a role in the photoprotective mechanism of all these three species.     

Early biochemical effects of Microcystis aeruginosa extracts on juvenile rainbow trout (Oncorhynchus mykiss)

Microcystins (MC) are usually the predominant cyanotoxins associated with cyanobacterial blooms in natural surface waters. These toxins are well-known hepatotoxic agents that proceed by inhibiting protein phosphatase in aquatic biota; recent studies have also reported oxidative stress and disruption of ion regulation in aquatic organisms. In the present study, young trout (Oncorhynchus mykiss) were exposed to crude extracts of Microsystis aeruginosa for four days at 15 °C. The level of microcystins was calculated to confirm the presence of toxins in these crude extracts: 0, 0.75, 1.8 and 5 μg/L. Protein phosphatase measured in the liver increased by at least 3-fold and is significantly as a result of exposure to these sublethal concentrations of crude extract, his indicates an early defense response against protein phosphatase inhibition from cyanotoxins. This was corroborated by the decreased phosphate content in proteins found in the liver and brain. No increase in glutathione-S transferase (GST) activity was observed and lipid peroxidation was unaffected in both liver and brain tissue exposed to the cyanobacterial extracts. The data revealed that the proportion of the reduced (metal-binding) form of metallothionein (MT) decreased by two-fold relative to the control group (with a concomitant increase in the proportion of the oxidized form). The level of phosphate associated with MT increased by 1.5-fold at the highest concentration of crude extract. Acetylcholinesterase (AChE) activity in brain tissue was decreased after exposure to the highest concentration of crude extract, suggesting a slowdown in neural activity. However, no biotransformation processes or detoxification of GST was triggered. Our findings show early sign of biochemical effects of MC-LR in young trout.     

Capsular polysaccharides facilitate enhanced iron acquisition by the colonial cyanobacterium Microcystis sp. isolated from a freshwater lake

Microcystis sp., especially in its colonial form, is a common dominant species during cyanobacterial blooms in many iron‐deficient water bodies. It is still not entirely clear, however, how the colonial forms of Microcystis acclimate to iron‐deficient habitats, and the responses of unicellular and colonial forms to iron‐replete and iron‐deficient conditions were examined here. Growth rates and levels of photosynthetic pigments declined to a greater extent in cultures of unicellular Microcystis than in cultures of the colonial form in response to decreasing iron concentrations, resulting in the impaired photosynthetic performance of unicellular Microcystis as compared to colonial forms as measured by variable fluorescence and photosynthetic oxygen evolution. These results indicate that the light‐harvesting ability and photosynthetic capacity of colonial Microcystis was less affected by iron deficiency than the unicellular form. The carotenoid contents and nonphotochemical quenching of colonial Microcystis were less reduced than those of the unicellular form under decreasing iron concentrations, indicating that the colonial morphology enhanced photoprotection and acclimation to iron‐deficient conditions. Furthermore, large amounts of iron were detected in the capsular polysaccharides (CPS) of the colonies, and more iron was found to be attached to the colonial Microcystis CPS under decreasing iron conditions as compared to unicellular cultures. These results demonstrated that colonial Microcystis can acclimate to iron deficiencies better than the unicellular form, and that CPS plays an important role in their acclimation advantage in iron‐deficient waters.     

Lower Methylation of the ANGPTL2 Gene in Leukocytes from Post-Acute Coronary Syndrome Patients

DNA methylation is believed to regulate gene expression during adulthood in response to the constant changes in environment. The methylome is therefore proposed to be a biomarker of health through age. ANGPTL2 is a circulating pro-inflammatory protein that increases with age and prematurely in patients with coronary artery diseases; integrating the methylation pattern of the promoter may help differentiate age- vs. disease-related change in its expression. We believe that in a pro-inflammatory environment, ANGPTL2 is differentially methylated, regulating ANGPTL2 expression. To test this hypothesis we investigated the changes in promoter methylation of ANGPTL2 gene in leukocytes from patients suffering from post-acute coronary syndrome (ACS). DNA was extracted from circulating leukocytes of post-ACS patients with cardiovascular risk factors and from healthy young and age-matched controls. Methylation sites (CpGs) found in the ANGPTL2 gene were targeted for specific DNA methylation quantification. The functionality of ANGPTL2 methylation was assessed by an in vitro luciferase assay. In post-ACS patients, C-reactive protein and ANGPTL2 circulating levels increased significantly when compared to healthy controls. Decreased methylation of specific CpGs were found in the promoter of ANGPTL2 and allowed to discriminate age vs. disease associated methylation. In vitro DNA methylation of specific CpG lead to inhibition of ANGPTL2 promoter activity. Reduced leukocyte DNA methylation in the promoter region of ANGPTL2 is associated with the pro-inflammatory environment that characterizes patients with post-ACS differently from age-matched healthy controls. Methylation of different CpGs in ANGPTL2 gene may prove to be a reliable biomarker of coronary disease.     

Photosynthetic adaptation to light availability shapes the ecological success of bloom-forming cyanobacterium Pseudanabaena to iron limitation

The poorly understood filamentous cyanobacterium Pseudanabaena is commonly epiphytic on Microcystis colonies and their abundances are often highly correlated during blooms. The response and adaptation of Microcystis to iron limitation have been extensively studied, but the strategies Pseudanabaena uses to respond to iron limitation are largely unknown. Here, physiological responses to iron limitation were compared between one Pseudanabaena and two Microcystis strains grown under different light intensities. The results showed that low-intensity light exacerbated, but high-intensity light alleviated, the negative effect of iron limitation on Pseudanabaena growth relative to two Microcystis strains. It was found that robust light-harvesting and photosynthetic efficiency allowed adaptation of Pseudanabaena to low light availability relative to two Microcystis strains only during iron sufficiency. The results also indicated that a larger investment in the photosynthetic antenna probably contributed to light/iron co-limitation of Pseudanabaena relative to two Microcystis strains under both light and iron limitation. Furthermore, the lower antenna pigments/chlorophyll a ratio and photosynthetic efficiency, and higher nonphotochemical quenching and saturation irradiance provided Pseudanabaena photoadaptation and photoprotection advantages over the two Microcystis strains under the high-light condition. The lower investment in antenna pigments of Pseudanabaena than the two Microcystis strains under high-light intensity is likely an efficient strategy for both saving iron quotas and decreasing photosensitivity. Therefore, when compared with Microcystis, the high plasticity of antenna pigments, along with the excellent photoadaptation and photoprotection ability of Pseudanabaena, probably ensures its ecological success under iron limitation when light is sufficient.