223 research outputs found
Acclimation to Hypoxia Increases Survival Time of Zebrafish, Danio rerio, during lethal hypoxia
Survivorship of zebrafish, Danio rerio, was measured during lethal hypoxic stress after pretreatment in water at either ambient oxygen or at a lowered, but nonlethal, level of oxygen. Acclimation to nonlethal hypoxia (pO2 @ 15 Torr; ca. 10% air-saturation) for 48 hr significantly extended survival time during more severe hypoxia (pO2 @ 8 Torr; ca. 5% air-saturation) compared to survival of individuals with no prior hypoxic exposure. The magnitude of the acclimation effect depended upon the sex of the fish: hypoxia pretreatment increased the survival times of males by a factor of approximately 9 and that of females by a factor of 3 relative to controls. In addition, survival time of control and hypoxia acclimated fish depended upon when in the year experiments were conducted. Survival times were 2–3 times longer when measured in the late fall or winter compared to survival times measured during the spring or summer. These results demonstrate a direct survival benefit of short-term acclimation to hypoxia in this genetically tractable fish. The fact that the acclimation effect depended upon the sex of the fish and the season during which experiments were conducted demonstrates that other genetic and/or environmental factors affect hypoxia tolerance in this species
Geographic Variation in the Effects of Heat Exposure on Maximum Sprint Speed and Hsp70 Abundance in Populations of the Western Fence Lizard, Scelopolus occidentalis
We examined whether western fence lizards Sceloporus occidentalis
occurring in thermally divergent environments display differential
responses to high temperature in locomotor performance
and heat-shock protein (Hsp) expression. We measured
maximum sprint speed in S. occidentalis from four populations
at paired latitudes and elevations before and after exposure to
an experimental heat treatment and then quantified hind-limb
muscle Hsp70 expression. Lizards collected from northern or
high-elevation collection sites suffered a greater reduction in
sprint speed after heat exposure than lizards collected from
southern or low-elevation sites. In addition, lizards from northern
collection sites also exhibited an increase in Hsp70 expression
after heat exposure, whereas there was no effect of
heat exposure on Hsp70 expression in lizards from southern
collection sites. Across all groups, there was a negative relationship
between Hsp70 expression and sprint speed after thermal
stress. This result is significant because (a) it suggests that
an increase in Hsp70 alone cannot compensate for the immediate
negative effects of high-temperature exposure on sprint
speed and (b) it demonstrates a novel correlation between an
emergent property at the intersection of several physiological
systems (locomotion) and a cellular response (Hsp70 expression).
Ultimately, geographic variation in the effects of heat on
sprint speed may translate into differential fitness and population
viability during future increases in global air temperatures
Geographic Variation in the Effects of Heat Exposure on Maximum Sprint Speed and Hsp70 Abundance in Populations of the Western Fence Lizard, Scelopolus occidentalis
We examined whether western fence lizards Sceloporus occidentalis
occurring in thermally divergent environments display differential
responses to high temperature in locomotor performance
and heat-shock protein (Hsp) expression. We measured
maximum sprint speed in S. occidentalis from four populations
at paired latitudes and elevations before and after exposure to
an experimental heat treatment and then quantified hind-limb
muscle Hsp70 expression. Lizards collected from northern or
high-elevation collection sites suffered a greater reduction in
sprint speed after heat exposure than lizards collected from
southern or low-elevation sites. In addition, lizards from northern
collection sites also exhibited an increase in Hsp70 expression
after heat exposure, whereas there was no effect of
heat exposure on Hsp70 expression in lizards from southern
collection sites. Across all groups, there was a negative relationship
between Hsp70 expression and sprint speed after thermal
stress. This result is significant because (a) it suggests that
an increase in Hsp70 alone cannot compensate for the immediate
negative effects of high-temperature exposure on sprint
speed and (b) it demonstrates a novel correlation between an
emergent property at the intersection of several physiological
systems (locomotion) and a cellular response (Hsp70 expression).
Ultimately, geographic variation in the effects of heat on
sprint speed may translate into differential fitness and population
viability during future increases in global air temperatures
Oxidative phosphorylation and the realkalinization of intracellular pH during recovery from anoxia in Artemia franciscana embryos
The contribution of mitochondrial oxidative phosphorylation to the realkalinization of intracellular pH (pHi) and resynthesis of purine nucleotides during recovery from anoxia was investigated in embryos of Artemia franciscana by assessing the sensitivity of mitochondrial respiration to pH, calculating proton consumption by oxidative phosphorylation, and measuring changes in pHi using 31P nuclear magnetic resonance. Following short-term anoxia, pHi increased from 6.7 to 7.7 during 20 min of aerobic recovery and was temporally correlated with a large increase in ATP. State 3 respiration rates of isolated mitochondria were not substantially compromised at the acidic pH corresponding to the pHi during anoxia (pH 6.3-6.8) compared to values obtained at pH 7.7. Both state 3 respiration rates and respiratory control ratios exhibited broad, substrate-specific pH optima, whereas state 4 respiration rates increased gradually with increasing pH. P:O flux ratios were near their mechanistic limits and did not vary appreciably with pH below 7.5. Estimates of intracellular buffering capacity indicate that between 18 and 37 mmol H+ (1 cytosol)-1 must be consumed to elevate pHi from 6.7 to 7.7. Phosphorylation of mono- and diphosphate purine-nucleotides during the first 20 min of recovery may account for the consumption of up to 4.79 mmol H+ (1 cytosol)-1. An additional 4.77 to 8.18 mmol H+ (1 cytosol)-1 may be consumed through the oxidation of mono- or dicarboxylic acids, respectively, in the Krebs cycle. Taken together, these data are consistent with a role for oxidative phosphorylation in the realkalinization of pHi and resynthesis of purine nucleotides in A. franciscana embryos during recovery from anoxia. © 1995
Oxygen Limitation and Tissue Metabolic Potential of the African Fish Barbus neumayeri: Roles of Native Habitat and Acclimatization
Background: Oxygen availability in aquatic habitats is a major environmental factor influencing the ecology, behaviour, and physiology of fishes. This study evaluates the contribution of source population and hypoxic acclimatization of the African fish, Barbus neumayeri, in determining growth and tissue metabolic enzyme activities. Individuals were collected from two sites differing dramatically in concentration of dissolved oxygen (DO), Rwembaita Swamp (annual average DO 1.35 mgO2 L-1) and Inlet Stream West (annual average DO 5.58 mgO2 L-1) in Kibale National Park, Uganda, and reciprocally transplanted using a cage experiment in the field, allowing us to maintain individuals under natural conditions of oxygen, food availability, and flow. Fish were maintained under these conditions for four weeks and sampled for growth rate and the activities of phosphofructokinase (PFK), lactate dehydrogenase (LDH), citrate synthase (CS), and cytochrome c oxidase (CCO) in four tissues, liver, heart, brain, and skeletal muscle. Results: Acclimatization to the low DO site resulted in lower growth rates, lower activities of the aerobic enzyme CCO in heart, and higher activities of the glycolytic enzyme PFK in heart and skeletal muscle. The activity of LDH in liver tissue was correlated with site of origin, being higher in fish collected from a hypoxic habitat, regardless of acclimatization treatment. Conclusions: Our results suggest that the influence of site of origin and hypoxic acclimatization in determining enzyme activity differs among enzymes and tissues, but both factors contribute to higher glycolytic capacity and lower aerobic capacity in B. neumayeri under naturally-occurring conditions of oxygen limitation
Sequence and functional characterization of hypoxia inducible factors, HIF1α, HIF2αa, and HIF3α, from the estuarine fish, Fundulus heteroclitus
Author Posting. © The Author(s), 2016. This is the author's version of the work. It is posted here under a nonexclusive, irrevocable, paid-up, worldwide license granted to WHOI. It is made available for personal use, not for redistribution. The definitive version was published in American Journal of Physiology-Regulatory Integrative and Comparative Physiology, 312 (2017): R412-R425, doi:10.1152/ajpregu.00402.2016.The hypoxia inducible factor (HIF) family of transcription factors plays central roles in
the development, physiology, pathology, and environmental adaptation of animals. Because
many aquatic habitats are characterized by episodes of low dissolved oxygen, fish represent ideal
models to study the roles of HIF in the response to aquatic hypoxia. The estuarine fish Fundulus
heteroclitus occurs in habitats prone to hypoxia, it responds to low oxygen via behavioral,
physiological, and molecular changes, and one member of the HIF family, HIF2α, has been
previously described. Herein, cDNA sequencing, phylogenetic analyses, and genomic
approaches were used to determine other members of the HIFα family from F. heteroclitus and
their relationships to HIFα subunits from other vertebrates. In vitro and cellular approaches
demonstrated that full-length forms of HIF1α, 2α, and 3α independently formed complexes with
the β subunit (ARNT) to bind to hypoxia response elements and activate reporter gene
expression. Quantitative PCR showed that HIFα mRNA abundance varied among organs of
normoxic fish in an isoform-specific fashion. Analysis of the F. heteroclitus genome revealed a
locus encoding a second HIF2α, HIF2αb, a predicted protein lacking oxygen sensing and
transactivation domains. Finally, sequence analyses demonstrated polymorphism in the coding
sequence of each F. heteroclitus HIFα subunit, suggesting that genetic variation in these
transcription factors may play a role in the variation in hypoxia responses among individuals or
populations.This research was supported in
part by the National Science Foundation (IBN-0236494 and DEB-1120263) and by National
Institute of Environmental Health Sciences (NIEHS) grant P42ES007381 (Superfund Basic
Research Program at Boston University). Data interpretation was aided by reference to a
preliminary draft of the F. heteroclitus genome sequence, which was supported by funding from
the National Science Foundation (collaborative research grants DEB-1120512, DEB-1265282,
DEB-1120013, DEB-1120263, DEB-1120333, DEB-1120398)
Effects of Long-Term Hypoxia on Enzymes of Carbohydrate Metabolism in the Gulf killifish, Fundulus grandis
The goal of the current study was to generate a comprehensive, multi-tissue perspective of the effects of chronic hypoxic exposure on carbohydrate metabolism in the Gulf killifish Fundulus grandis. Fish were held at approximately 1.3·mg·l–1 dissolved oxygen (~3.6·kPa) for 4·weeks, after which maximal activities were measured for all glycolytic enzymes in four tissues (white skeletal muscle, liver, heart and brain), as well as for enzymes of glycogen metabolism (in muscle and liver) and gluconeogenesis (in liver). The specific activities of enzymes of glycolysis and glycogen metabolism were strongly suppressed by hypoxia in white skeletal muscle, which may reflect decreased energy demand in this tissue during chronic hypoxia. In contrast, several enzyme specific activities were higher in liver tissue after hypoxic exposure, suggesting increased capacity for carbohydrate metabolism. Hypoxic exposure affected fewer enzymes in heart and brain than in skeletal muscle and liver, and the changes were smaller in magnitude, perhaps due to preferential perfusion of heart and brain during hypoxia. The specific activities of some gluconeogenic enzymes increased in liver during long-term hypoxic exposure, which may be coupled to increased protein catabolism in skeletal muscle. These results demonstrate that when intact fish are subjected to prolonged hypoxia, enzyme activities respond in a tissue-specific fashion reflecting the balance of energetic demands, metabolic role and oxygen supply of particular tissues. Furthermore, within glycolysis, the effects of hypoxia varied among enzymes, rather than being uniformly distributed among pathway enzymes
The Extraordinary Mid-infrared Spectrum of the Blue Compact Dwarf Galaxy SBS0335-052
SBS0335-052 is a blue compact dwarf galaxy (BCD) with one of the lowest known
metallicities, ZZ_{\sun}/41, making it a local example of how
primordial starburst galaxies and their precursors might appear. A spectrum
obtained with the Infrared Spectrograph (IRS) on the Spitzer Space Telescope
clearly shows silicate absorption features, emission lines of [SIV] and
[NeIII], and puts strong upper limits on the PAH emission features. The
observed low resolution spectrum (R~90) extends from 5.3 to 35microns and peaks
at ~28microns. The spectrum is compared to IRS observations of the prototypical
starburst nucleus NGC7714. SBS0335-052 is quite unlike normal starburst
galaxies, which show strong PAH bands, low ionization emission lines, and a
continuum peak near 80microns. The continuum difference for m
implies a substantial reduction in the mass of cold dust. If the spectrum of
this very low metallicity galaxy is representative of star forming galaxies at
higher redshifts, it may be difficult to distinguish them from AGNs which also
show relatively featureless flat spectra in the mid-IR.Comment: Accepted in ApJ Sup. Spitzer Special Issue, 4 pages, 2 figure
The ACS LCID project. VI. The SFH of the Tucana dSph and the relative ages of the isolated dSph galaxies
We present a detailed study of the star formation history (SFH) of the Tucana
dwarf spheroidal galaxy. High quality, deep HST/ACS data, allowed us to obtain
the deepest color-magnitude diagram to date, reaching the old main sequence
turnoff (F814 ~ 29) with good photometric accuracy. Our analysis, based on
three different SFH codes, shows that Tucana is an old and metal-poor stellar
system, which experienced a strong initial burst of star formation at a very
early epoch (~ 13 Gyr ago) which lasted a maximum of 1 Gyr (sigma value). We
are not able to unambiguously answer the question of whether most star
formation in Tucana occurred before or after the end of the reionization era,
and we analyze alternative scenarios that may explain the transformation of
Tucana from a gas-rich galaxy into a dSph. Current measurements of its radial
velocity do not preclude that Tucana may have crossed the inner regions of the
Local Group once, and so gas stripping by ram pressure and tides due to a close
interaction cannot be ruled out. On the other hand, the high star formation
rate measured at early times may have injected enough energy into the
interstellar medium to blow out a significant fraction of the initial gas
content. Gas that is heated but not blown out would also be more easily
stripped via ram pressure. We compare the SFH inferred for Tucana with that of
Cetus, the other isolated LG dSph galaxy in the LCID sample. We show that the
formation time of the bulk of star formation in Cetus is clearly delayed with
respect to that of Tucana. This reinforces the conclusion of Monelli et al.
(2010) that Cetus formed the vast majority of its stars after the end of the
reionization era implying, therefore, that small dwarf galaxies are not
necessarily strongly affected by reionization, in agreement with many
state-of-the-art cosmological models. [abridged]Comment: Accepted for publication on ApJ, 19 pages, 10 figures, 2 tables. A
version with full resolution figures is available at
http://www.iac.es/project/LCID/?p=publication
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