Studies on haemosiderin and ferritin from iron-loaded rat liver

Summary Haemosiderin has been isolated from siderosomes and ferritin from the cytosol of livers of rats iron-loaded by intraperitoneal injections of iron-dextran. Siderosomal haermosiderin, like ferritin, was shown by electron diffraction to contain iron mainly in the form of small particles of ferrihydrite (5Fe₂O₃ · 9H₂O), with average particle diameter of 5.36±1.31 nm (SD), less than that of ferritin iron-cores (6.14±1.18 nm). Mössbauer spectra of both iron-storage complexes are also similar, except that the blocking temperature,T _B, for haemosiderin (23 K) is lower than that of ferritin (35 K). These values are consistent with their differences in particle volumes assuming identical magnetic anisotropy constants. Measurements of P/Fe ratios by electron probe microanalysis showed the presence of phosphorus in rat liver haemosiderin, but much of it was lost on extensive dialysis. The presence of peptides reacting with anti-ferritin antisera and the similarities in the structures of their iron components are consistent with the view that rat liver haemosiderin arises by degradation of ferritin polypeptides, but its peptide pattern is different from that found in human-thalassaemia haemosiderin. The blocking temperature, 35 K, for rat liver ferritin is near to that reported, 40 K, for human-thalassaemia spleen ferritin. However, the haemosiderin isolated from this tissue, in contrast to that from rat liver, had aT _B higher than that of ferritin. The iron availability of haemosiderins from rat liver and human-thalassaemic spleen to a hydroxypyridinone chelator also differed. That from rat liver was equal to or greater, and that from human spleen was markedly less, than the iron availability from either of the associated ferritins, which were equivalent. The differences in properties of the two types of haemosiderin may reflect their origins from primary or secondary iron overload and differences in the duration of the overload.     

Operation of the glycolate pathway in isolated bundle sheath strands of maize and Panicum maximum

Operation of the glycolate pathway in isolated bundle sheath (BS) strands of two C₄ species was demonstrated from ¹⁴C incorporation into two intermediates, glycine and serine, under conditions favourable for photorespiratory activity. Isolated BS strands fixing ¹⁴CO₂ under light at physiological rates incorporate respectively 3% (Zea mays L., cv. INRA 258) and 7% (Panicum maximum Jacq.) of total ¹⁴C fixed into glycine + serine, at low bicarbonate levels (less than the Km for CO₂ fixation, 0.8 mM). Higher bicarbonate concentrations depressed the percentage of incorporation into the two amino acids. No labelling was observed in the absence of added glutamate. Oxygen was required for glycine + serine labelling, since ¹⁴C incorporation into glycine was largely depressed by argon flushing, and labelling of the two amino acids was nearly suppressed by the addition of the strong reductant, dithionite, especially in maize. Two inhibitors of the glycolate pathway were tested. With α-hydroxypyridine-methanesulfonic acid, an inhibitor of glycolate oxidase, labelling of glycine and serine remained minimal whereas glycolate was accumulated. Isoniazid, an inhibitor of the transformation of glycine to serine induced a 50% increased labelling of glycine in maize BS, and a large decrease in serine labelling. In Panicum, the increase in [¹⁴C]-glycine was 90%. These results suggest that the pathway glycolate → glycine → serine operates in these plants. However, leakage of metabolites occurs in BS cells, especially in maize and a large part of newly formed glycolate, glycine and serine is exported out of the cells. Operation of ribulose-1,5-bisphosphate oxygenase activity in competition with ribulose-1,5-bisphosphate carboxylase is demonstrated by the lowering of total ¹⁴CO₂ fixation when O₂ is increased at low bicarbonate concentration. An interesting feature observed in maize BS, at low bicarbonate concentration, was an increase in ribulose-1,5-bisphosphate labelling when the O₂ level was decreased. This was accompanied by an increase in CO₂ fixation. This could indicate an increased rate in synthesis of ribulose-1,5-bisphosphate (which accumulated) due to a stimulation of ATP synthesis by cyclic photophosphorylation under anaerobic conditions.     

Properties of the ATP-sensitive K+ current activated by levcromakalim in isolated pulmonary arterial myocytes

Tension and patch clamp recording techniques were used to investigate the relaxation of rabbit pulmonary artery and the properties of the K⁺ current activated by levcromakalim in isolated myocytes. Under whole-cell voltage clamp, holding at –60 mV in symmetrical 139 mm K⁺, levcromakalim (10 m) induced a noisy inward current of –116 ± 19 pA (n = 13) which developed over 1 to 2 min. This current could be blocked by either glibenclamide (10 m) or phencyclidine (5–50 M) and was unaffected when extracellular Ca²⁺ was removed. Both these drugs inhibited the levcromakalim-induced relaxation of muscle strips precontracted with 20 mm [K⁺] _o . Application of voltage ramps in symmetrical 139 mm K⁺ confirmed that the levcromakalim-induced current was carried by K⁺ ions and was weakly voltage dependent over the potential range from –100 to +40 mV.The unitary current amplitude and density of the channels underlying the levcromakalim-activated whole-cell K⁺ current was estimated from the noise in the current record. We estimate that levcromakalim caused activation of around 300 channels per cell, with a single channel current of 1.1 pA, corresponding to a slope conductance of about 19 pS. Furthermore, cells dialyzed with an ATP-free pipette solution developed a large noisy inward current at –60 mV, which could subsequently be blocked by flash photolysis of caged ATP. Analysis of the noise associated with this current indicated that the single channel amplitude underlying the ATP-blocked current was 1.4 pA, a value similar to that estimated for the levcromakalim-induced current. We conclude that the conductance of this ATP-sensitive channel is likely to be small under physiological conditions and that it is present at low density.We thank SmithKline & Beecham for the gift of levcromakalim, ICI Pharmaceuticals for the gift of charybdotoxin and Prof. D. Colquhoun for the noise analysis programs. We also thank Mr. R. Davey for technical assistance with tension experiments. This work was supported by the British Heart Foundation and the Wellcome Trust. L.H.C. is a Wellcome Research Fellow and P.L. is an intermediate fellow of the BHF.     

Evidence for the Predator Attraction Hypothesis in an amphibian predator–prey system

Many species possess damage-released chemical alarm cues that function in alerting nearby individuals to a predator attack. One hypothesis for the evolution and/or maintenance of such cues is the Predator Attraction Hypothesis, where predators, rather than prey, are the “intended” recipients of these cues. If a predator attack attracts additional predators, these secondary predators might interfere with the predation event, providing the prey with a better chance to escape. In this study, we conducted two experiments to explore this hypothesis in an amphibian predator/prey system. In Experiment 1, we found that tiger salamanders (Ambystoma mavortium) showed a foraging attraction to chemical cues from wood frog (Lithobates sylvaticus) tadpoles. Salamanders that were experienced with tadpole prey, in particular, were strongly attracted to tadpole alarm cues. In Experiment 2, we observed experimental encounters between a tadpole and either one or two salamanders. The presence of the second predator caused salamanders to increase attack speed at the cost of decreased attack accuracy (i.e., increasing the probability that the tadpole would escape attacks). We also found that the mere presence of visual and chemical cues from a second predator did not affect this speed/accuracy trade-off but did cause enough of a distraction to increase tadpole survival. Thus, our findings are consistent with the Predator Attraction Hypothesis for the evolution and/or maintenance of alarm cues.     

Developing Regenerate: A circular economy engagement tool for the assessment of new and existing buildings

The transition toward a circular economy (CE) is key in decarbonizing the built environment. Despite this, knowledge of—and engagement with—CE philosophies remains limited within the construction industry. Discussion with practitioners reveals this to be contributed to by a lack of clarity regarding CE principles, with numerous organizations recommending implementation of differing and sometimes conflicting principles. In addition, a systematic assessment of how building designs consider CE is made difficult by the multiple design areas required to be considered and the large amount of design data required to do so. The absence of a systematic CE assessment causes a lack of comparability across designs, preventing benchmarking of CE practices in building design at present. This paper details the development of Regenerate, a CE engagement tool for the assessment of new and existing buildings, established in an effort to overcome the aforementioned barriers to the adoption of CE within the construction sector. A CE design workflow for the built environment is proposed, comprising four overarching circularity principles (Design for Adaptability; Design for Deconstructability; Circular Material Selection; Resource Efficiency) and contributing design actions. In addition to engaging stakeholders by enabling the assessment of building designs, the tool retrieves key data for further research. Information on completed design actions as well as recycling and waste metrics is collected to facilitate future CE benchmarking. “Bill of materials” data (i.e., material quantities) is also compiled, with this being key in material stock modeling research and embodied carbon benchmarking.     

Environment outweighs the effects of fishing in regulating demersal community structure in an exploited marine ecosystem

Global climate change has already caused bottom temperatures of coastal marine ecosystems to increase worldwide. These ecosystems face many pressures, of which fishing is one of the most important. While consequences of global warming on commercial species are studied extensively, the importance of the increase in bottom temperature and of variation in fishing effort is more rarely considered together in these exploited ecosystems. Using a 17 year time series from an international bottom trawl survey, we investigated covariations of an entire demersal ecosystem (101 taxa) with the environment in the Celtic Sea. Our results showed that over the past two decades, biotic communities in the Celtic Sea were likely controlled more by environmental variables than fisheries, probably due to its long history of exploitation. At the scale of the entire zone, relations between taxa and the environment remained stable over the years, but at a local scale, in the center of the Celtic Sea, dynamics were probably driven by interannual variation in temperature. Fishing was an important factor structuring species assemblages at the beginning of the time series (2000) but decreased in importance after 2009. This was most likely caused by a change in spatial distribution of fishing effort, following a change in targeted taxa from nephrops to deeper water anglerfish that did not covary with fishing effort. Increasing bottom temperatures could induce additional changes in the coming years, notably in the cold‐water commercial species cod, hake, nephrops, and American plaice. We showed that analyzing covariation is an effective way to screen a large number of taxa and highlight those that may be most susceptible to future simultaneous increases in temperature and changes in exploitation pattern by fisheries. This information can be particularly relevant for ecosystem assessments.     

Evaluating the Mechanisms of Landscape Change on White-Tailed Deer Populations

Understanding how landscape change influences the distribution and densities of species, and the consequences of these changes, is a central question in modern ecology. The distribution of white-tailed deer (Odocoileus virginianus) is expanding across North America, and in some areas, this pattern has led to an increase in predators and consequently higher predation rates on woodland caribou (Rangifer tarandus caribou)—an alternate prey species that is declining across western Canada. Understanding the factors influencing deer distribution has therefore become important for effective conservation of caribou in Canada. Changing climate and anthropogenic landscape alteration are hypothesized to facilitate white-tailed deer expansion. Yet, climate and habitat alteration are spatiotemporally correlated, making these factors difficult to isolate. Our study evaluates the relative effects of snow conditions and human-modified habitat (habitat alteration) across space on white-tailed deer presence and relative density. We modeled deer response to snow depth and anthropogenic habitat alteration across a large latitudinal gradient (49° to 60°) in Alberta, Canada, using motion-sensitive camera data collected in winter and spring from 2015 to 2019. Deer distribution in winter and spring were best explained by models including both snow depth and habitat alteration. Sites with shallower snow had higher deer presence regardless of latitude. Increased habitat alteration increased deer presence in the northern portion of the study area only. Winter deer density was best explained by snow depth only, whereas spring density was best explained by both habitat alteration and the previous winter's snow depth. Our results suggest that limiting future habitat alteration or restoring habitat can alter deer distribution, thereby potentially slowing or reversing expansion, but that climate plays a significant role beyond what managers can influence. © 2020 The Wildlife Society.     

Tolerance of young allis shad Alosa alosa (Clupeidae) to oxy-thermic stress

The ecology of the young stages of allis shad Alosa alosa is poorly documented, although they can be exposed to many pressures during their freshwater phase and their downstream migration. When passing through systems such as the Gironde-Garonne-Dordogne watershed (GGD, SW France), they can be subjected to high temperatures and low levels of oxygen (hypoxia). The aim of this work is to assess the tolerance of young Alosa alosa at four ages (c. 10, 30, 60 and 85 days old) by challenging them to different temperatures (18, 22, 26 and 28°C) together with decreasing oxygen saturation levels (from 100% to 30%). Survival of the 10-day-old individuals was not influenced by oxy-thermic conditions, but high stress levels were detected and perhaps this age class was too fragile regarding the constraint of the experimental design. Survival at 30 and at 60 days old was negatively influenced by the highest temperatures tested alone (from 26°C and from 28°C, respectively) but no effect was detected at 85 days old up to 28°C. A combined effect of temperature and oxygen level was highlighted, with heat accelerating survival decrease when associated with oxygen level depletion: essentially, survival was critical (<50%) at 30 days old at temperature ≥22°C together with 30% O₂; at 60 days old, at temperature = 28°C with 30% O₂; at 85 days old, at temperature ≥26°C with ≤40% O₂. Tolerance to oxy-thermic pressures appeared to be greater among the migratory ages (60 and 85 days old) than among the 30-day-old group. Based on environmental data recorded in the GGD system and on our experimental results, an exploratory analysis allowed a discussion of the possible impact of past oxy-thermic conditions on the local population dynamics between 2005 and 2018. The oxy-thermic conditions that may affect Alosa alosa at ages when they migrate downstream (60 and 85 days old) were not frequently recorded in this period, except in cases of extreme episodes of heat together with hypoxia that occurred in some years, in summertime in the turbidity maximum zone of the Gironde estuary (particularly in the year 2006). Interestingly, oxy-thermic conditions that are likely to threaten the 30-day-old individuals occurred more frequently in the lower freshwater parts of the GGD system between the years 2005 and 2018. In the context of climate change, a general increase in temperature is predicted, as well as more frequent and severe hypoxic events, therefore we suggest that local Alosa alosa population recruitment could encounter critical oxy-thermic conditions more frequently in the future if no adaptive management of water resources occurs.