Catalysis by KDM6 Histone Demethylases - A Synergy between the Non-Heme Iron(II) Center, Second Coordination Sphere, and Long-Range Interactions.

KDM6A (UTX) and KDM6B (JMJD3) are human non-heme Fe(II) and 2-oxoglutarate (2OG) dependent JmjC oxygenases that catalyze the demethylation of trimethylated lysine 27 in the N-terminal tail of histone H3, a post-translational modification that regulates transcription. A Combined Quantum Mechanics/ Molecular Mechanics (QM/MM) and Molecular Dynamics (MD) study on the catalytic mechanism of KDM6A/B reveals that the transition state for the rate-limiting hydrogen atom transfer (HAT) reaction in KDM6A catalysis is stabilized by polar (Asn217) and aromatic (Trp369)/non-polar (Pro274) residues in contrast to KDM4, KDM6B and KDM7 demethylases where charged residues (Glu, Arg, Asp) are involved. KDM6A employs both σ- and π-electron transfer pathways for HAT, whereas KDM6B employs the σ-electron pathway. Differences in hydrogen bonding of the Fe-chelating Glu252(KDM6B) contribute to the lower energy barriers in KDM6B vs. KDM6A. The study reveals a dependence of the activation barrier of the rebound hydroxylation on the Fe-O-C angle in the transition state of KDM6A. Anti-correlation of the Zn-binding domain with the active site residues is a key factor distinguishing KDM6A/B from KDM7/4s. The results reveal the importance of communication between the Fe center, second coordination sphere, and long-range interactions in catalysis by KDMs and, by implication, other 2OG oxygenases.

The Efficacy of Ingesting Water on Thermoregulatory Responses and Running Performance in a Warm-Humid Condition.

The understanding that fluid ingestion attenuates thermoregulatory and circulatory stress during exercise in the heat was based on studies conducted in relatively dry (∼50% RH) environments. It remains undetermined whether similar effects occur during exercise in a warm and more humid environment, where evaporative capacity is reduced. Nine well-trained, unacclimatised male runners were randomly assigned to perform four experimental trials where they ran for 60 min at an intensity of 70% VO2max followed by an incremental exercise test until volitional exhaustion. The four trials consisted of non-fluid ingestion (NF) and fluid ingestion (FI) in a warm-dry (WD) and warm-humid condition (WH). Time to exhaustion (TTE), body temperature (Tb), whole body sweat rate, partitional calorimetry measures, heart rate and plasma volume were recorded during exercise. There was no significant difference in Tb following 60 min of exercise in FI and NF trial within both WD (37.3°C ± 0.4 vs. 37.4°C ± 0.3; p > 0.05) and WH conditions (38.0°C ± 0.4 vs. 38.1°C ± 0.4; p > 0.05). The TTE was similar between FI and NF trials in both WH and WD, whereas exercise capacity was significantly shorter in WH than WD (9.1 ± 2.8 min vs. 12.7 ± 2.4 min, respectively; p = 0.01). Fluid ingestion failed to provide any ergogenic benefit in attenuating thermoregulatory and circulatory stress during exercise in the WH and WD conditions. Consequently, exercise performance was not enhanced with fluid ingestion in the warm-humid condition, although the humid environment detrimentally affected exercise endurance.

Heterologous expression of the human polybromo-1 protein in the methylotrophic yeast Pichia pastoris.

The human polybromo-1 protein (BAF180) is a known driver mutation in clear cell renal cell carcinoma, where it is mutated in approximately 40% of cases. BAF180 is the chromatin-targeting subunit of the PBAF complex. BAF180 has six bromodomains, two BAH domains, and one HMG box. Bromodomains are known to recognize acetylated-lysines on histones and play a role in nucleosome recognition. BAH domains are required for ubiquitination of PCNA, a key regulator of DNA damage. The putative HMG box, if functional, may be involved in DNA-binding. While the binding specificities of individual bromodomains have been studied by our lab and others, the results have failed to reach a consensus. The acetyl-histone binding features of the full-length protein is unknown and is the motivation for this work. The hypothetical HMG and BAH domains have not been studied and the actual function of these regions is currently unknown. Thus, the precise interactions of this large and complex protein are not well-studied. Advances in understanding this large protein have been hindered by the inability to express and purify recombinant full-length BAF180 protein. Currently, only phenomenological studies using BAF180 expressed in mammalian cells have been conducted. Here, we report the successful expression, purification of full-length biologically active BAF180 protein using the GAP promoter in the heterologous host Pichia pastoris. The ability to express full-length and mutated BAF180 will allow for biophysical binding studies. Knowledge of the binding interactions is critical for us to understand the role of BAF180 in cancer development and its progression.

Cardiovascular adjustments to heat stress during prolonged exercise.

Prolonged effort in hot environments is increasing popular in extreme sports. The number of long distance athletes taking part in races in extremely warm condition, as in deserts, is larger than in the past and also the race distances are increased thus. The demanding for the heart function are higher than those challenged in the past only by few athletes and in easier conditions. This puts news challenges on the professional involved in these activities and there is a need to better understand how the cardiocirculatory system responses in these extreme environmental conditions. This review paper is focused on the mechanism of cardiovascular drift function during prolonged exercise in heat conditions. Many aspects are treated in the literature. The emerging topics treated in this paper are the sympathetic and vagal nervous activity, heart rate functioning during exercise, dehydration and hyperthermia, the relationships between heart rate and stroke volume oxygen uptake and blood flow dynamic, circulatory responses, left ventricular functions in athletes after strenuous prolonged exercise, and heart rate variability. The literature on the topic appear to be vast and address many important factors of interest for the performance development occurred in hot condition and necessary to be known for the preservation of the health of the athletes.

BAF180: Its Roles in DNA Repair and Consequences in Cancer.

In 2011, Varela et al. reported that the PBRM1 gene is mutated in approximately 40% of clear cell renal cell carcinoma cases. Since then, the number of studies relating PBRM1 mutations to cancers has substantially increased. BAF180 has now been linked to more than 30 types of cancers, including ccRCC, cholangiocarcinomas, esophageal squamous cell carcinoma, bladder cancer, and breast cancer. The mutations associated with BAF180 are most often truncations, which result in a loss of protein expression. This loss has been shown to adversely affect the expression of genes, likely because BAF180 is the chromatin recognition subunit of PBAF. In addition, BAF180 functions in numerous DNA repair mechanisms. Its roles in mediating DNA repair are likely the mechanism by which BAF180 acts a tumor suppressor protein. As research on this protein gains more interest, scientists will begin to piece together the complicated puzzle of the BAF180 protein and why its loss often results in cancer.

Practical Use of Metal Oxide Semiconductor Gas Sensors for Measuring Nitrogen Dioxide and Ozone in Urban Environments.

The potential of inexpensive Metal Oxide Semiconductor (MOS) gas sensors to be used for urban air quality monitoring has been the topic of increasing interest in the last decade. This paper discusses some of the lessons of three years of experience working with such sensors on a novel instrument platform (Small Open General purpose Sensor (SOGS)) in the measurement of atmospheric nitrogen dioxide and ozone concentrations. Analytic methods for increasing long-term accuracy of measurements are discussed, which permit nitrogen dioxide measurements with 95% confidence intervals of 20.0 µ g m - 3 and ozone precision of 26.8 µ g m - 3 , for measurements over a period one month away from calibration, averaged over 18 months of such calibrations. Beyond four months from calibration, sensor drift becomes significant, and accuracy is significantly reduced. Successful calibration schemes are discussed with the use of controlled artificial atmospheres complementing deployment on a reference weather station exposed to the elements. Manufacturing variation in the attributes of individual sensors are examined, an experiment possible due to the instrument being equipped with pairs of sensors of the same kind. Good repeatability (better than 0.7 correlation) between individual sensor elements is shown. The results from sensors that used fans to push air past an internal sensor element are compared with mounting the sensors on the outside of the enclosure, the latter design increasing effective integration time to more than a day. Finally, possible paths forward are suggested for improving the reliability of this promising sensor technology for measuring pollution in an urban environment.

Central activation, metabolites, and calcium handling during fatigue with repeated maximal isometric contractions in human muscle.

PURPOSE: To determine the roles of calcium (Ca2+) handling by sarcoplasmic reticulum (SR) and central activation impairment (i.e., central fatigue) during fatigue with repeated maximal voluntary isometric contractions (MVC) in human muscles. METHODS: Contractile performance was assessed during 3 min of repeated MVCs (7-s contraction, 3-s rest, n = 17). In ten participants, in vitro SR Ca2+-handling, metabolites, and fibre-type composition were quantified in biopsy samples from quadriceps muscle, along with plasma venous [K+]. In 11 participants, central fatigue was compared using tetanic stimulation superimposed on MVC in quadriceps and adductor pollicis muscles. RESULTS: The decline of peak MVC force with fatigue was similar for both muscles. Fatigue resistance correlated directly with % type I fibre area in quadriceps (r = 0.77, P = 0.009). The maximal rate of ryanodine-induced Ca2+-release and Ca2+-uptake fell by 31 ± 26 and 28 ± 13%, respectively. The tetanic force depression was correlated with the combined reduction of ATP and PCr, and increase of lactate (r = 0.77, P = 0.009). Plasma venous [K+] increased from 4.0 ± 0.3 to 5.4 ± 0.8 mM over 1-3-min exercise. Central fatigue occurred during the early contractions in the quadriceps in 7 out of 17 participants (central activation ratio fell from 0.98 ± 0.05 to 0.86 ± 0.11 at 1 min), but dwindled at exercise cessation. Central fatigue was seldom apparent in adductor pollicis. CONCLUSIONS: Fatigue with repeated MVC in human limb muscles mainly involves peripheral aspects which include impaired SR Ca2+-handling and we speculate that anaerobic metabolite changes are involved. A faster early force loss in quadriceps muscle with some participants is attributed to central fatigue.

The effects of a systematic increase in relative humidity on thermoregulatory and circulatory responses during prolonged running exercise in the heat.

This study examined the thermoregulatory and circulatory responses, and exercise performance of trained distance runners during exercise in the heat (31°C) at varying relative humidity (RH). In a randomized order, 11 trained male distance runners performed 5 60 min steady-state runs at a speed eliciting 70% of VO2max in RH of 23, 43, 52, 61 and 71%. This was followed immediately with an incremental exercise test to volitional exhaustion. Core (Tre) and mean skin temperature (T¯sk), cardiac output (Q), heart rate (HR), and stroke volume (SV) were recorded at regular intervals. A significant (P = 0.003) main effect was detected for RH on mean body temperature (Tb), with a significantly higher Tb detected during steady-state exercise in the 61 and 71% RH compared to that in the 23% RH. During the steady-state exercise, no differences were detected in whole body sweat loss (P = 0.183). However, a significant main effect of RH was observed for HR and SV (P = 0.001 and 0.006, respectively) but not Q (P = 0.156). The time to exhaustion of the incremental exercise test was significantly reduced at 61 and 71% RH compared with 23% RH (P = 0.045 and 0.005, respectively). Despite an increase in dry heat loss, a greater thermoregulatory and circulatory stress was evident during steady-state exercise at 61 and 71% RH. This ultimately limits the capacity to perform the subsequent incremental exercise to exhaustion. This study highlighted that in a warm environment, the range of the prescriptive zone progressively narrows as RH increases.

Thermal and Cardiovascular Strain Mitigate the Potential Benefit of Carbohydrate Mouth Rinse During Self-Paced Exercise in the Heat.

PURPOSE: To determine whether a carbohydrate mouth rinse can alter self-paced exercise performance independently of a high degree of thermal and cardiovascular strain. METHODS: Eight endurance-trained males performed two 40-km cycling time trials in 35°C, 60% RH while swilling a 20-ml bolus of 6.5% maltodextrin (CHO) or a color- and taste-matched placebo (PLA) every 5 km. Heart rate, power output, rectal temperature (Tre), and mean skin temperature (Tsk) were recorded continuously; cardiac output, oxygen uptake (VO2), mean arterial pressure (MAP), and perceived exertion (RPE) were measured every 10 min. RESULTS: Performance time and mean power output were similar between treatments, averaging 63.9 ± 3.2 and 64.3 ± 2.8 min, and 251 ± 23 and 242 ± 18 W in CHO and PLA, respectively. Power output, stroke volume, cardiac output, MAP, and VO2 decreased during both trials, increasing slightly or remaining stable during a final 2-km end-spurt. Tre, Tsk, heart rate, and RPE increased throughout exercise similarly with both treatments. Changes in RPE correlated with those in Tre (P < 0.005) and heart rate (P < 0.001). CONCLUSIONS: These findings suggest that carbohydrate mouth rinsing does not improve ~1-h time trial performance in hot-humid conditions, possibly due to a failure in down-regulating RPE, which may be influenced more by severe thermal and cardiovascular strain.

Impact of an Educational Program for Advanced Practice Nurses on Knowledge of Kidney Disease Outcomes Quality Initiative Guidelines.

Patients with chronic kidney disease (CKD) are often referred to a nephrologist late. Contributing factors include primary care providers' lack of awareness of practice guidelines for treating kidney disease and their uncertainty of timing for referral to a nephrologist. The purpose of this quasi-experimental study was to determine if advanced practice nurses working in primary care are knowledgeable about the National Kidney Foundations Kidney Disease Outcomes Quality Initiative Guidelines, if a CKD education program increases knowledge, and if knowledge is retained. Fourteen advanced practice nurses participated in the study. The knowledge outcome was measured using a CKD knowledge-based survey. The results showed a significant increase in knowledge post-intervention; moreover, knowledge gained was retained at the one-month follow-up intervaL This evidence-based practice project was developed to promote timely referral to a nephrologist, which may then slow the progression of kidney disease, decrease morbidity and mortality, and reduce healthcare cost.

The evolutionary genetics of highly divergent alleles of the mimicry locus in Papilio dardanus.

BACKGROUND: The phylogenetic history of genes underlying phenotypic diversity can offer insight into the evolutionary origin of adaptive traits. This is especially true where single genes have large phenotypic effects, for example in determining polymorphic mimicry in butterflies. Here, we characterise the evolutionary history of two candidate genes for the mimicry switch in the polymorphic Batesian mimic Papilio dardanus coding for the transcription factors engrailed and invected. RESULTS: We show that phased haplotypes associated with the dominant morphs f. poultoni and f. planemoides are phylogenetically highly divergent, in particular at non-synonymous sites. Some non-synonymous changes are shared between the divergent alleles suggesting either convergence or a shared ancestry. Gene trees for invected do not show this pattern. Despite their great divergence, all engrailed alleles of P. dardanus were monophyletic with respect to alleles of closely related species. Phylogenetic analyses therefore reveal no evidence for introgression from other species. A McDonald-Kreitman test conducted on a population sample from South Africa confirms a significant excess of intraspecific non-synonymous diversity in P. dardanus engrailed, suggesting long-term balanced polymorphism at this locus. CONCLUSIONS: The divergence between engrailed haplotypes suggests an evolutionary history distorted by selection with multiple changes reflecting recurrent selective sweeps. The high level of intraspecific polymorphism observed is characteristic of balancing selection on this locus, as expected if the gene engrailed is under phenotypic selection for the maintenance of multiple mimetic morphs. Non-synonymous changes in key functional portions of a major transcription factor are likely to be deleterious but if maintained in a dominant allele at low frequency, heterozygosity would reduce the associated genetic load.

Comparative genomics of the mimicry switch in Papilio dardanus.

The African Mocker Swallowtail, Papilio dardanus, is a textbook example in evolutionary genetics. Classical breeding experiments have shown that wing pattern variation in this polymorphic Batesian mimic is determined by the polyallelic H locus that controls a set of distinct mimetic phenotypes. Using bacterial artificial chromosome (BAC) sequencing, recombination analyses and comparative genomics, we show that H co-segregates with an interval of less than 500 kb that is collinear with two other Lepidoptera genomes and contains 24 genes, including the transcription factor genes engrailed (en) and invected (inv). H is located in a region of conserved gene order, which argues against any role for genomic translocations in the evolution of a hypothesized multi-gene mimicry locus. Natural populations of P. dardanus show significant associations of specific morphs with single nucleotide polymorphisms (SNPs), centred on en. In addition, SNP variation in the H region reveals evidence of non-neutral molecular evolution in the en gene alone. We find evidence for a duplication potentially driving physical constraints on recombination in the lamborni morph. Absence of perfect linkage disequilibrium between different genes in the other morphs suggests that H is limited to nucleotide positions in the regulatory and coding regions of en. Our results therefore support the hypothesis that a single gene underlies wing pattern variation in P. dardanus.

Characterising the phenotypic diversity of Papilio dardanus wing patterns using an extensive museum collection.

The history of 20th Century evolutionary biology can be followed through the study of mimetic butterflies. From the initial findings of discontinuous polymorphism through the debates regarding the evolution of mimicry and the step-size of evolutionary change, to the studies on supergene evolution and molecular characterisation of butterfly genomes, mimetic butterflies have been at the heart of evolutionary thought for over 100 years. During this time, few species have received as much attention and in-depth study as Papilio dardanus. To assist all aspects of mimicry research, we present a complete data-derived overview of the extent of polymorphism within this species. Using historical samples permanently held by the NHM London, we document the extent of phenotypic variation and characterise the diversity present in each of the subspecies and how it varies across Africa. We also demonstrate an association between "imperfect" mimetic forms and the transitional race formed in the area where Eastern and Western African populations meet around Lake Victoria. We present a novel portal for access to this collection, www.mimeticbutterflies.org, allowing remote access to this unique repository. It is hoped that this online resource can act as a nucleus for the sharing and dissemination of other collections databases and imagery connected with mimetic butterflies.

Adjustments in the force-frequency relationship during passive and exercise-induced hyperthermia.

INTRODUCTION: We examined the extent to which fatiguing cycling exercise in the heat influences contractile function in modulating the force-frequency relationship. METHODS: Before (∽37.0 °C) and after (∽38.5 °C) exercise (ExH) and passive (PaH) hyperthermia, an 8-s train of stimulation at 10, 20, 50, and 100 Hz (2 s per frequency) and a potentiated twitch were evoked on the relaxed knee extensors using percutaneous stimulation. RESULTS: ExH and PaH produced a decrease in the 20:50 Hz force ratio, indicative of low-frequency fatigue (P < 0.01). This adjustment was more pronounced after ExH than PaH (P < 0.01). A rightward displacement in the force-frequency relationship occurred after ExH and PaH (P < 0.05) and was exacerbated by ExH (P < 0.05). Peak twitch force also decreased after ExH (P < 0.05). CONCLUSIONS: ExH reduces force summation due to development of skeletal muscle fatigue, exacerbating the shift in force-frequency to the right relative to PaH.

Peptide-directed self-assembly of functionalized polymeric nanoparticles part I: design and self-assembly of peptide-copolymer conjugates into nanoparticle fibers and 3D scaffolds.

A robust self-assembly of nanoparticles into fibers and 3D scaffolds is designed and fabricated by functionalizing a RAFT-polymerized amphiphilic triblock copolymer with designer ionic complementary peptides so that the assembled core-shell polymeric nanoparticles are directed by peptide assembly into continuous "nanoparticle fibers," ultimately leading to 3D fiber scaffolds. The assembled nanostructure is confirmed by FESEM and optical microscopy. The assembly is not hindered when a protein (insulin) is incorporated within the nanoparticles as an active ingredient. MTS cytotoxicity tests on SW-620 cell lines show that the peptides, copolymers, and peptide-copolymer conjugates are biocompatible. The methodology of self-assembled nanoparticle fibers and 3D scaffolds is intended to combine the advantages of a flexible hydrogel scaffold with the versatility of controlled release nanoparticles to offer unprecedented ability to incorporate desired drug(s) within a self-assembled scaffold system with individual control over the release of each drug.

Plasma and lymphocyte Hsp72 responses to exercise in athletes with prior exertional heat illness.

We investigated the effect of exercise in the heat on both intracellular and extracellular Hsp72 in athletes with a prior history of exertional heat illness (EHI). Two groups of runners, one consisting of athletes who had a previous history of EHI, and a control group (CON) of similar age (29.7 ± 1.2 and 29.1 ± 2 years CON vs. EHI) and fitness [maximal oxygen consumption [Formula: see text] 65.7 ± 2 and 64.5 ± 3 ml kg(-1) min(-1) CON vs. EHI] were recruited. Seven subjects in each group ran on a treadmill for 1 h at 72 % [Formula: see text] in warm conditions (30 °C, 40 % RH) reaching rectal temperatures of ~39.3 (CON) and ~39.2 °C (EHI). Blood was collected every 10 min during exercise and plasma was analysed for extracellular Hsp72. Intracellular Hsp72 levels were measured in both monocytes and lymphocytes before and immediately after the 60-min run, and then after 1 h recovery at an ambient temperature of 24 °C. Plasma Hsp72 increased from 1.18 ± 0.14 and 0.86 ± 0.08 ng/ml (CON vs. EHI) at rest to 4.56 ± 0.63 and 4.04 ± 0.45 ng/ml (CON vs. EHI, respectively) at the end of exercise (p < 0.001), with no difference between groups. Lymphocyte Hsp72 was lower in the EHI group at 60 min of exercise (p < 0.05), while monocyte Hsp72 was not different between groups. The results of the present study suggest that the plasma Hsp72 response to exercise in athletes with a prior history of EHI remained similar to that of the CON group, while the lymphocyte Hsp72 response was reduced.

Exercise-heat acclimation in young and older trained cyclists.

OBJECTIVES: The purpose of this study was to investigate the effect of age on the capacity to acclimatise to exercise-heat stress. This study hypothesised that age would not affect body temperature and heat loss effector responses to short-term exercise-heat acclimation in trained subjects. DESIGN: Seven young subjects (19-32 years) were matched with 7 older subjects (50-63 years). Subjects were highly trained but not specifically heat acclimated when they exercised for 60 min at 70%VO2max in hot-dry (35 °C, 40%RH) and thermoneutral (20 °C, 40%RH) conditions, pre and post 6 days of exercise-heat acclimation (70%VO2max, 35 °C, 40%RH). METHODS: Rectal temperature (Tr), skin temperature (Tsk), heart rate (HR), cutaneous vascular conductance (CVC) and whole body sweat loss (Msw) were measured during each testing session and Tr and HR were measured during each acclimation session. RESULTS: Tr, Tsk, %HRmax, CVC and Msw were similar across age groups both pre and post heat acclimation. Following heat acclimation relative decreases and increases in Tr and Msw, respectively, were similar in both subject groups. There was a significant reduction in heart rate (%HRmax) and increase in final CVC following the acclimation programme in the young group (all p < 0.05) but not the older group. CONCLUSIONS: When comparing young and older well trained adults we found age affected the cardiovascular adaptation but not body temperature or whole body sweat loss to exercise-heat acclimation. These data suggest age does not affect the capacity to acclimatise to exercise-heat stress in highly trained adults undergoing short-term heat acclimation.

Enhanced performance with elastic resistance during the eccentric phase of a countermovement jump.

PURPOSE: To identify the effect of additional elastic force on the kinetic and kinematic characteristics, as well as the magnitude of leg stiffness, during the performance of accentuated countermovement jumps (CMJs). METHODS: Fifteen trained male subjects performed 3 types of CMJ including free CMJ (FCMJ; ie, body weight), ACMJ-20, and ACMJ-30 (ie, accentuated eccentric CMJ with downward tensile force equivalent to 20% and 30% body mass, respectively). A force platform synchronized with 6 high-speed infrared cameras was used to measure vertical ground-reaction force (VGRF) and displacement. RESULTS: Using downward tensile force during the lowering phase of a CMJ and releasing the bands at the start of the concentric phase increased maximal concentric VGRF (6.34%), power output (23.21%), net impulse (16.65%), and jump height (9.52%) in ACMJ-30 compared with FCMJ (all P < .05). However, no significant difference was observed in the magnitude of leg stiffness between the 3 modes of jump. The results indicate that using downward recoil force of the elastic material during the eccentric phase of a CMJ could be an effective method to enhance jump performance by applying a greater eccentric loading on the parallel and series elastic components coupled with the release of stored elastic energy. CONCLUSIONS: The importance of this finding is related to the proposition that power output, net impulse, takeoff velocity, and jump height are the key parameters for successful athletic performance, and any training method that improves impulse and power production may improve sports performance, particularly in jumping aspects of sport.

Influence of heat stress and exercise intensity on vastus lateralis muscle and prefrontal cortex oxygenation.

This study examined whether a rise in thermal and cardiovascular strain during exercise to exhaustion in the heat at different intensities is associated with compromised muscle and cerebral oxygenation. Using near-infrared spectroscopy, oxygenation changes in the vastus lateralis and prefrontal cortex of ten subjects cycling to exhaustion in 40 °C conditions at 60 % (H60%) and 75 % (H75%) maximal oxygen uptake (VO2(max)) and for 60 min in 18 °C conditions at 60 % VO2(max) (C60%) were examined. Thermoregulatory and cardiovascular responses were also monitored. Rectal temperature reached 38.1 °C in the C60% trial, 39.7 °C (~60 min) and 39.0 °C (~27 min) in the H60% and H75% trials, respectively (P < 0.001). The core-to-skin temperature gradient was similarly narrow (~0.9 °C) at exhaustion in the heat, occurring >97 % of maximum heart rate and accompanied by significant declines in stroke volume, cardiac output and mean arterial pressure (P < 0.01). Vastus lateralis oxygen saturation (SmO(2)) declined at the onset of exercise in all conditions, remaining similarly depressed at exhaustion in the heat. Prefrontal cortex oxygen saturation (ScO(2)) was ~10 % lower at exhaustion in the H60% and H75% trials compared with C60% (P < 0.01), which remained above baseline from 15 min onward. These findings indicate that changes in SmO(2) and ScO(2) are associated with the development of thermal and cardiovascular strain during exercise to exhaustion in the heat, which is accelerated by exercise intensity. In locomotor muscles, a potential reduction in oxygen delivery may develop, whereas in the brain, the progressive reduction in ScO(2) may induce mental fatigue.

Specific training improves skeletal muscle mitochondrial calcium homeostasis after eccentric exercise.

There is limited understanding of the mitochondrial adaptation following repeated eccentric exercise bouts, a model resulting in muscle adaptation known as the repeat bout effect. It was hypothesized that downhill training would reduce mitochondrial calcium content (MCC) post an acute eccentric bout with concurrent improvements in mitochondrial respiratory function. Thirty-four Sprague-Dawley rats were divided into four groups: control (N), control with acute eccentric exercise (N (ecc)), trained control (X) and trained with acute eccentric exercise (X (ecc)). Training for X and X (ecc) consisted of 30 min per day for five consecutive days of downhill treadmill running. The acute eccentric exercise bout was a -14° treadmill exercise for 90 min performed 2 weeks after the training period. Animals were killed 48 h post-exercise. Isolated mitochondria from the red quadriceps allowed for the measure of mitochondrial respiratory indices and MCC. Calpain activity and heat shock protein 72 expression (HSP72) were also measured. MCC dramatically increased following the acute bout of eccentric exercise in N (ecc) (p < 0.001), but did not change in X (ecc). Mitochondrial respiratory function tended to be slightly depressed in N (ecc) (state 3 respiration, p = 0.053; respiratory control ratio, p = 0.098) and unaltered in X (ecc). Previous training altered the calpain and heat shock protein response to an acute bout of eccentric exercise. The results suggest that downhill exercise training improves mitochondrial calcium homeostasis following an acute bout of prolonged eccentric exercise and may stabilize mitochondrial respiratory function. These improvements coincide with a reduction in calpain activity and heat shock protein upregulation.