In Saccharomyces cerevisiae, the diffusion rate of hydrogen peroxide (H2O2) through the plasma membrane decreases during adaptation to H2O2 by means of a mechanism that is still unknown. Here, evidence is presented that during adaptation to H2O2 the anisotropy of the plasma membrane increases. Adaptation to H2O2 was studied at several times (15min up to 90min) by applying the steady-state H2O2 delivery model. For wild-type cells, the steady-state fluorescence anisotropy increased after 30min, or 60min, when using 2-(9-anthroyloxy) stearic acid (2-AS), or diphenylhexatriene (DPH) membrane probe, respectively. Moreover, a 40% decrease in plasma membrane permeability to H2O2 was observed at 15min with a concomitant two-fold increase in catalase activity. Disruption of the ergosterol pathway, by knocking out either ERG3 or ERG6, prevents the changes in anisotropy during H2O2 adaptation. H2O2 diffusion through the plasma membrane in S. cerevisiae cells is not mediated by aquaporins since the H2O2 permeability constant is not altered in the presence of the aquaporin inhibitor mercuric chloride. Altogether, these results indicate that the regulation of the plasma membrane permeability towards H2O2 is mediated by modulation of the biophysical properties of the plasma membrane.
Eurasian otter, Lutra lutra (L., 1758), spraints collected at the Aguieira hydroelectric dam (central Portugal, n = 916) and tributaries (n = 412) were analysed to assess diet compared with prey availability. Fish and crayfish abundances in the reservoir were assessed with fyke and trammel nets. Prey availability in the tributaries was estimated by electrofishing. In both the reservoir and its tributaries, fish were the main prey and consisted predominantly of Lepomis gibbosus (L., 1758) (60%–65% of occurrences), which is an introduced species of Centrachidae that is abundant in the reservoir but is almost absent in the tributaries. These data suggest that otters using the tributaries feed predominantly in the reservoir. Seasonal dietary variations corresponded to increased availability of nonfish prey categories. Capture vs. consumption analyses demonstrated that otters did not consume L. gibbosus according to its availability. In fact, L. gibbosus was consumed less frequently when other prey species were more available (e.g., amphibians, eels, barbells). The tributaries offer important otter refuge areas that are scarce at the edge of the reservoir, and so, in large reservoirs care should be taken to minimize disturbance in the surrounding catchments. Results indicate that otter populations make use of these conjoint systems to ensure their survival.
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