Journal of Comparative Physiology B-Biochemical Systems and Environmental Physiology最新文献

While oxygen is essential for oxidative phosphorylation, O₂ can form reactive species (ROS) when interacting with electrons of mitochondrial electron transport system. ROS is dependent on O₂ pressure (PO₂) and has traditionally been assessed in O₂ saturated media, PO₂ at which mitochondria do not typically function in vivo. Mitochondrial ROS can be significantly elevated by the respiratory complex II substrate succinate, which can accumulate within hypoxic tissues, and this is exacerbated further with reoxygenation. Intertidal species are repetitively exposed to extreme O₂ fluctuations, and have likely evolved strategies to avoid excess ROS production. We evaluated mitochondrial electron leakage and ROS production in permeabilized brain of intertidal and subtidal triplefin fish species from hyperoxia to anoxia, and assessed the effect of anoxia reoxygenation and the influence of increasing succinate concentrations. At typical intracellular PO₂, net ROS production was similar among all species; however at elevated PO₂, brain tissues of the intertidal triplefin fish released less ROS than subtidal species. In addition, following in vitro anoxia reoxygenation, electron transfer mediated by succinate titration was better directed to respiration, and not to ROS production for intertidal species. Overall, these data indicate that intertidal triplefin fish species better manage electrons within the ETS, from hypoxic-hyperoxic transitions.

For ureosmotic marine elasmobranchs, the acquisition and retention of nitrogen is critical for the synthesis of urea. To better understand whole-body nitrogen homeostasis, we investigated mechanisms of nitrogen trafficking in North Pacific spiny dogfish (Squalus acanthias suckleyi). We hypothesized that the presence of nitrogen within the spiral valve lumen would affect both the transport of nitrogen and the mRNA abundance of a urea transporter (UT) and two ammonia transport proteins (Rhp2, Rhbg) within the intestinal epithelium. The in vitro preincubation of intestinal tissues in NH₄Cl, intended to simulate dietary nitrogen availability, showed that increased ammonia concentrations did not significantly stimulate the net uptake of total urea or total methylamine. We also examined the mRNA abundance of UT, Rhp2, and Rhbg in the gills, kidney, liver, and spiral valve of fasted, fed, excess urea fed, and antibiotic-treated dogfish. After fasting, hepatic UT mRNA abundance was significantly lower, and Rhp2 mRNA in the gills was significantly higher than the other treatments. Feeding significantly increased Rhp2 mRNA levels in the kidney and mid spiral valve region. Both excess urea and antibiotics significantly reduced Rhbg mRNA levels along all three spiral valve regions. The antibiotic treatment also significantly diminished UT mRNA abundance levels in the anterior and mid spiral valve, and Rhbg mRNA levels in the kidney. In our study, no single treatment had significantly greater influence on the overall transcript abundance of the three transport proteins compared to another treatment, demonstrating the dynamic nature of nitrogen balance in these ancient fish.

Commercially important trout species, especially rainbow trout, are under great threat due to several negative factors affecting oxygen levels in water such as global warming and eutrophication. In our study, rainbow trout (Oncorhynchus mykiss) was exposed to chronic (for 28 days) hypoxia (4.0 ± 0.5 mg/L) and hyperoxia (12 ± 1.2 mg/L) in order to evaluate the alteration of fatty acid profiles in muscle, liver and gill tissues. In addition, delta-6-desaturase and elongase gene expression profiles were measured in liver, kidney and gill tissues. The amount of saturated fatty acids increased by oxygen applications in the liver, while it decreased in the muscle and gill tissues compared to normoxia (p < 0.05). Monounsaturated fatty acids levels increased in muscle and gill (p < 0.05). Although n-3 polyunsaturated fatty acid (PUFA) decreased in muscle tissue, n-6 PUFA increased (p < 0.05). The n-3/n-6 ratio decreased in muscle tissue in response to the both exposures (p < 0.05) as well as eicosapentaenoic acid/docosahexaenoic acid ratio (p < 0.05). Hypoxia exposure generally increased delta-6-desaturase and elongase mRNA levels in all tissues (p < 0.05). However, gene expression profiles were variable in fish exposed to hyperoxia. As a result of oxygen exposures, the lipid profile of muscle tissue, which stores dense fat, was negatively affected more than that of liver and gill tissues. We determined that the change in expression levels was tissue specific.

The gill oxygen limitation hypothesis (GOLH) suggests that hypometric scaling of metabolic rate in fishes is a consequence of oxygen supply constraints imposed by the mismatched growth rates of gill surface area (a two-dimensional surface) and body mass (a three-dimensional volume). GOLH may, therefore, explain the size-dependent spatial distribution of fish in temperature- and oxygen-variable environments through size-dependent respiratory capacity, but this question is unstudied. We tested GOLH in the tidepool sculpin, Oligocottus maculosus, a species in which body mass decreases with increasing temperature- and oxygen-variability in the intertidal, a pattern consistent with GOLH. We statistically evaluated support for GOLH versus distributed control of [Formula: see text] allometry by comparing scaling coefficients for gill surface area, standard and maximum [Formula: see text] ([Formula: see text]_,Standard and [Formula: see text]_,Max, respectively), ventricle mass, hematocrit, and metabolic enzyme activities in white muscle. To empirically evaluate whether there is a proximate constraint on oxygen supply capacity with increasing body mass, we measured [Formula: see text]_,Max across a range of Po₂s from normoxia to P_crit, calculated the regulation value (R), a measure of oxyregulatory capacity, and analyzed the R-body mass relationship. In contrast with GOLH, gill surface area scaling either matched or was more than sufficient to meet [Formula: see text] demands with increasing body mass and R did not change with body mass. Ventricle mass (b = 1.22) scaled similarly to [Formula: see text]_,Max (b = 1.18) suggesting a possible role for the heart in the scaling of [Formula: see text]_,Max. Together our results do not support GOLH as a mechanism structuring the distribution of O. maculosus and suggest distributed control of oxyregulatory capacity.

Lactation is the most energetically demanding physiological process that occurs in mammalian females, and as a consequence of this energy expenditure, lactating females produce an enormous amount of excess heat. This heat is thought to limit the amount of milk a mother produces, and by improving heat dissipation, females may improve their milk production and offspring quality. Here we used SKH-1 hairless mice as a natural model of improved heat dissipation. Lactating mothers were given access to a secondary cage to rest away from their pups, and this secondary cage was kept either at room temperature (22 °C) in the control rounds or cooled to 8 °C in the experimental groups. We hypothesized that the cold exposure would maximize the heat dissipation potential, leading to increased milk production and healthier pups even in the hairless mouse model. However, we found the opposite, where cold exposure allowed mothers to eat more food, but they produced smaller weight pups at the end of lactation. Our results suggest that mothers prioritize their own fitness, even if it lowers the fitness of their offspring in this particular mouse strain. This maternal-offspring trade-off is interesting and requires future studies to understand the full interaction of maternal effects and offspring fitness in the light of the heat dissipation limitation.

The kinetics of myosin controls the speed and power of muscle contraction. Mammalian skeletal muscles express twelve kinetically different myosin heavy chain (MyHC) genes which provides a wide range of muscle speeds to meet different functional demands. Myogenic progenitors from diverse craniofacial and somitic mesoderm specify muscle allotypes with different repertoires for MyHC expression. This review provides a brief synopsis on the historical and current views on how cell lineage, neural impulse patterns, and thyroid hormone influence MyHC gene expression in muscles of the limb allotype during development and in adult life and the molecular mechanisms thereof. During somitic myogenesis, embryonic and foetal myoblast lineages form slow and fast primary and secondary myotube ontotypes which respond differently to postnatal neural and thyroidal influences to generate fully differentiated fibre phenotypes. Fibres of a given phenotype may arise from myotubes of different ontotypes which retain their capacity to respond differently to neural and thyroidal influences during postnatal life. This gives muscles physiological plasticity to adapt to fluctuations in thyroid hormone levels and patterns of use. The kinetics of MyHC isoforms vary inversely with animal body mass. Fast 2b fibres are specifically absent in muscles involved in elastic energy saving in hopping marsupials and generally absent in large eutherian mammals. Changes in MyHC expression are viewed in the context of the physiology of the whole animal. The roles of myoblast lineage and thyroid hormone in regulating MyHC gene expression are phylogenetically the most ancient while that of neural impulse patterns the most recent.

Holometabolous insects undergo metamorphosis to reconstruct their body to the adult form during pupal period. Since pupae cannot take any diets from the outside because of a hard pupal cuticle, those insects stock up on nutrients sufficient for successful metamorphosis during larval feeding period. Among those nutrients, carbohydrates are stored as glycogen or trehalose, which is the major blood sugar in insects. The hemolymph trehalose is constantly high during the feeding period but suddenly decreases at the beginning of the prepupal period. It is believed that trehalase, which is a trehalose-hydrolyzing enzyme, becomes highly active to reduce hemolymph trehalose level during prepupal period. This change in the hemolymph trehalose level has been interpreted as the physiological shift from storage to utilization of trehalose at that stage. Although this shift in trehalose physiology is indispensable for energy production required for successful metamorphosis, little is known on the regulatory mechanisms of trehalose metabolism in accordance with developmental progress. Here, we show that ecdysone, an insect steroid hormone, plays essential roles in the regulation of soluble trehalase activity and its distribution in the midgut of silkworm, Bombyx mori. In the end of larval period, soluble trehalase was highly activated in the midgut lumen. This activation was disappeared in the absence of ecdysone and also restored by ecdysone administration. Our present results suggest that ecdysone is essentially required for the changes in the function of the midgut on trehalose physiology as development progresses.

Several earthworm species are known to be able to withstand freezing. At the biochemical level, this ability is based on cryoprotectant accumulation as well as several other mechanisms. In this study, we used ¹H NMR to investigate metabolomic changes in two freeze-tolerant earthworm taxa, Dendrobaena octaedra and one of the genetic lineages of Eisenia sp. aff. nordenskioldi f. pallida. A total of 45 metabolites were quantified. High concentrations of glucose were present in frozen tissues of both taxa. No other putative cryoprotectants were found. We detected high levels of glycolysis end products and succinate in frozen animals, indicating the activation of glycolysis. Concentrations of many other substances also significantly increased. On the whole, metabolic change in response to freezing was much more pronounced in the specimens of Eisenia sp. aff. nordenskioldi f. pallida, including signs of nucleotide degradation.

The activity of superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GSH-Px), glutathione reductase (GR), and glutathione S-transferase (GST), as well as the concentrations of sulfhydryl (SH) groups and glutathione (GSH) were analyzed in five age classes of the Mediterranean centipede Scolopendra cingulata as follows: embryo, adolescens, maturus junior, maturus, and maturus senior. The data obtained showed the presence of SOD, CAT, GSH-Px, GR, GST, and SH groups in embryos. The transition from embryo to adolescens was accompanied by an increase in the activities of all studied enzymes, in response to the increased production of ROS due to the increased metabolic activity of the centipede associated with growth and development. Our results show that trends in antioxidant enzyme (AOE) activities were not uniform among adult age classes, suggesting that maturus junior, maturus, and maturus senior differentially respond and/or have different susceptibility to ROS. On the other hand, GSH concentration in embryos was undetectable, highest in adolescens and decreased in the latter part of life. Pearson correlation analysis in embryos showed that the activities of the AOEs were strongly and positively correlated with each other but negatively correlated with GSH and SH groups. At later age classes, SOD, CAT, GSH-Px, GR, GSH, and SH groups were no longer significantly correlated with GST. In the discriminant analysis, the variables that separated the age classes were GR, GST, SH groups, and body length. Body length was directly related to the age of individuals, clearly indicating that development/aging affects the regulation of antioxidant defense in this species.