Effect of polychlorinated biphenyls (PCBs) on phospholipid membrane fluidity

Changes of Heart Rate and Lipid Composition in Mytilus Edulis and Modiolus Modiolus Caused by Crude Oil Pollution and Low Salinity Effects

Blue mussels, Mytilus edulis, inhabiting tidal zones, are naturally exposed to fluctuating environmental conditions (e.g., fluctuations in temperature and salinities), while horse mussels, Modiolus modiolus, live under relatively invariable shelf water conditions. The present investigation tested the hypothesis: blue mussels, in comparison to horse mussels, have an increased ability to tolerate the stress of pollution combined with low salinity. To assess the response of blue mussels and horse mussels to oil pollution at seawater salinities of 25 psu (normal) and 15 psu (low), we used a combination of heart rate and lipid composition as physiological and biochemical indicators, respectively. A sharp decrease in heart rate as well as important fluctuations in cardiac activity was observed under all oil concentrations. Modifications in the concentrations of the main membrane lipid classes (phosphatidylcholine, phosphatidylethanolamine, and cholesterol) and storage lipids (primarily triacylglycerols) in response to different crude oil concentrations were time- and dose-dependent. Both chosen indicators showed a high sensitivity to crude oil contamination. Furthermore, both bivalve species showed similar responses to oil pollution, suggesting a universal mechanism for biochemical adaptation to crude oil pollution.

PCB-153 and temperature cause restructuring of goldfish membranes: homeoviscous response to a chemical fluidiser

Ortho-substituted PCBs intercalate between membrane phospholipids similarly to cholesterol and increase fluidity. Ectothermic animals have a well-developed homeoviscous response to counter the fluidising effect of temperature and avoid the disruption of membrane proteins. However, it remains unknown whether chemical fluidisation can also activate a homeoviscous response or interfere with normal acclimation to temperature. The fatty acid composition and cholesterol content of membranes from gill, white muscle, liver, and brain was measured in goldfish exposed to 4 treatments in a 2 × 2 factorial design (acclimated to 5 or 20°C, and exposed or not to PCB-153). The expression of Δ6 and Δ9 desaturases was also measured in gill and liver because these enzymes modulate changes in membrane unsaturation. We hypothesised that thermal and chemical stress would cause similar adjustments in phospholipid unsaturation, membrane cholesterol, and desaturase expression. Results show that PCB-153 triggers a homeoviscous response by changing cholesterol content in liver (+51%) and brain (+216%), as well as the double bond index in gills (-17%). In response to higher temperature, the membranes of gill, muscle, and brain substitute polyunsaturated fatty acids such as arachidonate [20:4] and eicosadienoate [20:2] with saturated fatty acids such as palmitate [16:0] and stearate [18:0]. Each tissue has a distinct pattern of changes, suggesting that different local factors contribute to the stress response. It is also possible that the thermal tolerance of individual species influences the homeoviscous response because the changes observed in goldfish liver are not consistent with what has been reported for trout liver. No evidence supporting the activation of desaturase expression could be found. Overall, and contrary to expectation, modulating membrane cholesterol is the main mechanism used to cope with PCB-153, whereas changes in unsaturation dominate temperature acclimation. If also present in other species, these protective responses may prove particularly important for polar fish that face the combined effects of thermal stress from climate change and chemical stress from organochlorine deposition. This study is the first to show that in vivo exposure to a membrane fluidiser can cause a homeoviscous response in an ectothermic animal. We conclude that the homeostatic mechanisms that preserve normal membrane function vary: (1) with the nature of the stress that perturbs fluidity, (2) with local conditions within each tissue, and (3) possibly with the thermal tolerance of individual species. These complicating factors will have to be considered in future studies of homeoviscous adjustments.

The impact of heavy metals on the grey garden slug, Deroceras reticulatum (Müller): Metal storage, cellular effects and semi-quantitative evaluation of metal toxicity

Laboratory-reared grey garden slugs, Deroceras reticulatum, were exposed to soil and food treated with solutions of three metal salts (CdCl2, ZnCl2, PbCl2) in three environmentally relevant concentrations, each for 21 days. Metal concentrations were determined in the soil, food and slugs by atomic absorption spectrophotometry (AAS). Zinc was localized ultrastructurally in the hepatopancreatic cells by means of energy-filtering transmission electron microscopy (EFTEM). Zinc, and also high amounts of copper, could be detected by electron spectroscopical imaging (ESI) and electron energy loss spectroscopy (EELS) in spherites of the basophilic cells. Ultrastructural responses to metal impact were investigated in two cell types of the hepatopancreas (digestive and basophilic cells) and the cellular responses were found to be dose- and metal-dependent. In order to evaluate the toxicity of the respective metal concentrations to the slugs, the ultrastructural reactions were semi-quantified and summarized as complex reaction patterns of numerous organelles. This novel approach provides a basis for the use of data from standardized tests as a background for risk assessment studies in the field.

Steady-State Effects of 2,5,2′,5′-Tetrachlorobiphenyl on Growth, Photosynthesis, and P Uptake in Selenastrum capricornutum

The steady-state effect of 2,5,2′,5′-tetrachlorobiphenyl (TCBP) on the green alga Selenastrum capricornutum was investigated in a P-limited two-stage chemostat system. The partition coefficient of this polychlorinated biphenyl congener was 5.9 × 10 4 in steady-state cultures. At a cellular TCBP concentration of 12.2 × 10 −8 ng · cell −1 , growth rate was not affected. However, photosynthetic capacity ( P max ) was significantly enhanced by TCBP (56 × 10 −9 μmol of C · cell −1 · h −1 versus 34 × 10 −9 μmol of C · cell −1 · h −1 in the control). Photosynthetic efficiency, or the slope of the photosynthesis-irradiance curve, was also significantly higher. There was little difference in the cell chlorophyll a content, and therefore the difference in these photosynthetic characteristics was the same even when they were expressed on a per-chlorophyll a basis. Cell C content was higher in TCBP-containing cells than in TCBP-free cells, but approximately 36% of the C fixed by cells with TCBP was not incorporated as cell C. The maximum P uptake rate was also enhanced by TCBP, but the half-saturation concentration appeared to be unaffected.