Bubble formation in crustaceans following decompression from hyperbaric gas exposures

In vivo bubble formation was studied in various crustaceans equilibrated with high gas pressures and rapidly decompressed to atmospheric pressure. The species varied widely in susceptibility to bubble formation, and adults were generally more susceptible than larval stages. Bubbles did not form in early brine shrimp larvae unless equilibration pressures of at least 175 atm argon or 350 atm helium were used; for adult brine shrimp, copepods, and the larvae of crabs and shrimps, 100-125 atm argon or 175-225 atm helium were required. In contrast, bubbles formed in the leg joints of megalopa and adult crabs following decompression from only 3-10 atm argon; stimulation of limb movements increased this bubble formation, whereas inhibition of movements decreased it. High hydrostatic compressions applied before gas equilibration or slow compressions did not affect bubble formation. We concluded that circulatory systems, musculature, and storage lipids do not necessarily render organisms susceptible to bubble formation and that bubbles do not generally originate as preformed nuclei. In some cases, tribonucleation appears to be the cause of the bubbles.     

Crystallization behavior and thermal properties of melt-crystallized poly[(R)-3-hydroxybutyric acid-co-6-hydroxyhexanoic acid] films.

Melt-crystallized films of poly[(R)-3-hydroxybutyric acid-co-10mol% 6-hydroxyhexanoic acid] (P[(R)-3HB-co-6HH]) were prepared by isothermal crystallization at various temperatures for 3 days, and subsequently stored at room temperature after the films formed well-developed and volume-filled spherulites. The lamellar morphologies and properties of melt-crystallized films were characterized by means of wide-angle X-ray diffraction, small-angle X-ray scattering, differential scanning calorimetry, transmission electron microscopy, and atomic force microscopy. The melting endotherm of P[(R)-3HB-co-6HH] films was composed of a broad peak starting around room temperature and of a sharper peak starting above the isothermal crystallization temperature. The stacking of flat-on lamellae with lamellar periodicity of 8-10 nm was detected on the surface of P[(R)-3HB-co6HH] films after the primary crystallization at 110 degrees C. On storage at room temperature above the Tg (-5 degrees C) of copolyester, thin crystals of 1-4 nm thickness appeared on the surface of P[(R)-3HB-co-6HH] films crystallized at 110 degrees C. These results suggest that long sequences of (R)-3HB units in a random copolyester form relatively thick P[(R)-3HB] crystalline lamellae during the primary crystallization process at a given crystallization temperature, while shorter sequences of (R)-3HB units, which are incapable of crystallizing at a given crystallization temperature, form relatively thin crystalline lamellae during the subsequent crystallization process at room temperature.     

Artificial expression of aquaporin-3 improves the survival of mouse oocytes after cryopreservation

Successful cryopreservation of mammalian cells requires rapid transport of water and cryoprotective solutes across the plasma membrane. Aquaporin-3 is known as a water/solute channel that can transport water and neutral solutes such as glycerol. In this study we examined whether artificial expression of aquaporin-3 in mouse oocytes can improve water and glycerol permeability and oocyte survival after cryopreservation. Immature mouse oocytes were injected with aquaporin-3 cRNA and were cultured for 12 h. Then the hydraulic conductivity (L(P)) and glycerol permeability (P(GLY)) of matured oocytes were determined from the relative volume changes in 10% glycerol in PB1 medium at 25 degrees C. Mean +/- SD values of L(P) and P(GLY) of cRNA-injected oocytes (3.09 +/- 1.22 micro m min(-1) atm(-1) and 3.69 +/- 1.47 x 10(-3) cm/min, respectively; numbers of oocytes = 25) were significantly higher than those of noninjected oocytes (0.83 +/- 0.02 micro m min(-1) atm(-1) and 0.07 +/- 0.02 x 10(-3) cm/min, respectively; n = 13) and water-injected oocytes (0.87 +/- 0.10 micro m min(-1) atm(-1) and 0.08 +/- 0.02 x 10(-3) cm/min, respectively; n = 20). After cryopreservation in a glycerol-based solution, 74% of cRNA-injected oocytes (n = 27) survived as assessed by their morphological appearance, whereas none of the water-injected oocytes survived (n = 10). When cRNA-injected oocytes that survived cryopreservation were inseminated in vitro, the penetration rate was 40% (n = 48) and the cleavage rate was 31% (n = 70), showing that oocytes retain their ability to be fertilized. This is the first report to show that artificial expression of a water/solute channel in a cell improves its survival after cryopreservation. This approach may enable cryopreservation of cells that have been difficult to cryopreserve.     

High oxygen transfer rate in a new aeration system using hollow fiber membrane

A new type of bubble aeration column called a hollow fiber membrane (HFM) aeration column was proposed, which was featured in the use of hollow fiber membranes and gave a high bubble density in the column. The value of k(L)a was increased by modifying the membrane surface for making the pore size smaller. The Sauter mean diameter of bubbles (D(vs)) was 2.0 +/- 0.1 mm in the range of the superficial gas velocity from 0.02 m s(-1) to 0.065 m s(-1), while that obtained for the bubbles near the membrane was 811 mum at the superficial gas velocity of 4.0 x 10(-4) m s(-1). The difference was ascribed to the effect of coalescence of bubbles. The value of K(L)a increased in proportion to the superficial gas velocity up to 0.02 m s(-1), and was almost constant above 0.03 m s(-1). The maximum value of k(L)a, 2.5 s(-1), was higher than those of the other aeration columns reported previously. The pneumatic power consumption per unit liquid volume (P(v)) for obtaining the same k(L)a was the smallest in the HFM aeration columns. P(v), for obtaining the same interfacial area of bubbles per liquid volume, was also lower than those for other types of aeration columns. It was suggested from the measurement of bubble diameter that the larger interfacial area generated in the HFM aeration column ascribes to the larger gas holdup than the smaller D(vs). (c) 1992 John Wiley & Sons, Inc.     

Generation of high-affinity antibody against T cell-dependent antigen in the Ganp gene-transgenic mouse

Generation of high-affinity Ab is impaired in mice lacking germinal center-associated DNA primase (GANP) in B cells. In this study, we examined the effect of its overexpression in ganp transgenic C57BL/6 mice (Ganp(Tg)). Ganp(Tg) displayed normal phenotype in B cell development, serum Ig levels, and responses against T cell-independent Ag; however, it generated the Ab with much higher affinity against nitrophenyl-chicken gammaglobulin in comparison with C57BL/6. To further examine the affinity increase, we established hybridomas producing high-affinity mAbs and compared their affinities using BIAcore. C57BL/6 generated high-affinity anti-nitrophenyl mAbs (K(D) approximately 2.50 x 10(-7) M) of IgG1/lambda1 and contained the V(H)186.2 region with W33L mutation. Ganp(Tg) generated much higher affinity (K(D) > 1.57 x 10(-9) M) by usage of V(H)186.2 as well as noncanonical V(H)7183 regions. Ganp(Tg) also generated exceptionally high-affinity anti-HIV-1 (V3 peptide) mAbs (K(D) > 9.90 x 10(-11) M) with neutralizing activity. These results demonstrated that GANP is involved in V region alteration generating high-affinity Ab.     

Relationship between weight of rescuer and quality of chest compression during cardiopulmonary resuscitation

Background

According to the guidelines for cardiopulmonary resuscitation (CPR), the rotation time for chest compression should be about 2 min. The quality of chest compressions is related to the physical fitness of the rescuer, but this was not considered when determining rotation time. The present study aimed to clarify associations between body weight and the quality of chest compression and physical fatigue during CPR performed by 18 registered nurses (10 male and 8 female) assigned to light and heavy groups according to the average weight for each sex in Japan.

Methods

Five-minute chest compressions were then performed on a manikin that was placed on the floor. Measurement parameters were compression depth, heart rate, oxygen uptake, integrated electromyography signals, and rating of perceived exertion. Compression depth was evaluated according to the ratio (%) of adequate compressions (at least 5 cm deep).

Results

The ratio of adequate compressions decreased significantly over time in the light group. Values for heart rate, oxygen uptake, muscle activity defined as integrated electromyography signals, and rating of perceived exertion were significantly higher for the light group than for the heavy group.

Conclusion

Chest compression caused increased fatigue among the light group, which consequently resulted in a gradual fall in the quality of chest compression. These results suggested that individuals with a lower body weight should rotate at 1-min intervals to maintain high quality CPR and thus improve the survival rates and neurological outcomes of victims of cardiac arrest.     

Human respiration at rest in rapid compression and at high pressures and gas densities

Ventilation (V), end-tidal PCO2 (PACO2), and CO2 elimination rate were measured in men at rest breathing CO2-free gas over the pressure range 1-50 ATA and the gas density range 0.4-25 g/l, during slow and rapid compressions, at stable elevated ambient pressures and during slow decompressions in several phases of Predictive Studies III-1971 and Predictive Studies IV-1975. Inspired O2 was at or near natural O2 levels during compressions and at stable high pressures; it was 0.5 ATA during decompressions. Rapid compressions to high pressures did not impair respiratory homeostasis. Progressive increase in pulmonary gas flow resistance due to elevation of ambient pressure and inspired gas density to the He-O2 equivalent of 5,000 feet of seawater was not observed to progressively decrease resting V, or to progressively increase resting PACO2. Rather, a complex pattern of change in PACO2 was seen. As both ambient pressure and pulmonary gas flow resistance were progressively raised, PACO2 at first increased, went through a maximum, and then declined towards values near the 1 ATA level. It is suggested that this pattern of PACO2 change results from interaction on ventilation of 1) increase in pulmonary resistance due to elevation of gas density with 2) increase in respiratory drive postulated as due to generalized CNS excitation associated with exposure to high hydrostatic pressure. There may be a similar interaction between increased gas flow resistance and increase in respiratory drive related to nitrogen partial pressure and the narcosis resulting therefrom.     

Matrix resistance stress: A key parameter for immobilized cell growth regulation

Microenvironmentally restricted yeast cell growth within Ca-alginate beads with and without entrapped gas bubbles was considered based on experimental data. Cell growth dynamics was described by (1) the dimensionless cell number density as a function of the cell growth time and (2) the cell distribution per bead cross sections. One of the key control parameters for bioprocess optimization is the matrix resistance stress generated during immobilized cell expansion. The dynamics of the increase in matrix stress was described theoretically based on a multi-scale mathematical model. In order to estimate and reduce the accumulation of matrix stress we considered repeated stress relaxation cycles in separate rheological experiments without immobilized cells.The results revealed that the increase in resistance stress within the Ca-alginate matrix was significant (∼7 kPa) after 10 repeated cycles, even under a low compression strain of 2% per cycle. The stress could be reduced by using the Ca-alginate matrix with entrapped gas bubbles. The final cell concentration within the beads with entrapped bubbles was 3.3 times higher in comparison with the beads without bubbles. The bubbles could locally amortize the compression effects within the surrounding cell clusters.     

Intracellular Bubble Formation: Differences in Gas Supersaturation Tolerances Between Tetrahymena and Euglena1

Cells of Tetrahymena pyriformis, T. thermophila, and Euglena gracilis were saturated with nitrogen gas at pressures up to 300 atm and rapidly decompressed. Damage was assessed by measuring post-decompression cell fragmentation or viability. Occurrence of intracellular bubbles was determined by cinephotomicrography performed during the decompression or by direct observations afterwards. The extreme gas supersaturations induced led to intracellular bubble formation and rupture in cells of Tetrahymena that contained food vacuoles, but only with supersaturations of 175 atm or higher; 225 atm left few cells intact. Bubbles were never observed in cells of Euglena or in Tetrahymena cells freed of food vacuoles, even when they were decompressed from substantially higher nitrogen supersaturations. Cells of Euglena were most resistant and were unaffected by supersaturations up to 250 atm.     

Bubble formation in crabs induced by limb motions after decompression

In vivo bubble formation was studied in the megalopal stage of the crab Pachygrapsus crassipes. The animals were equilibrated with elevated argon, nitrogen, or helium pressures then rapidly decompressed to atmospheric pressure. Voluntary motions induced bubble nucleation in leg joints after exposures to as low as 2 atm nitrogen (gauge pressure). Delays of several minutes sometimes passed between decompression and bubble formation. Mechanically stimulating the animals to move their legs increased this bubble formation, whereas immobilizing the legs before gas equilibration prevented it, even in animals decompressed from 150 atm nitrogen. We conclude that preformed nuclei are not responsible for bubbles developing in the legs of this animal. Instead, tribonucleation of bubbles apparently occurs as a result of limb motions at relatively low gas supersaturations.     

Hyperbaric oxygen may reduce gas bubbles in decompressed prawns by eliminating gas nuclei.

It is accepted that gas bubbles grow from preexisting gas nuclei in tissue. The possibility of eliminating gas nuclei may be of benefit in preventing decompression sickness. In the present study, we examined the hypothesis that hyperbaric oxygen may replace the resident gas in the nuclei with oxygen and, because of its metabolic role, eliminate the nuclei themselves. After pretreatment with oxygen, prawns were 98% saturated with nitrogen before explosive decompression at 30 m/min. Ten transparent prawns were exposed to four experimental profiles in a crossover design: 1) 10-min compression to 203 kPa with air; 2) 10-min compression with oxygen; 3) 10-min compression with oxygen to 203 kPa followed by 12 min air at 203 kPa; and 4) 10 min in normobaric oxygen followed by compression to 203 kPa with air. Bubbles were measured after explosive decompression. We found that pretreatment with hyperbaric oxygen (profile C) significantly reduces the number of bubbles and bubble volume. We suggest that hyperbaric oxygen eliminates bubble nuclei in the prawn.     

The influence of polymeric membrane gas spargers on hydrodynamics and mass transfer in bubble column bioreactors

Gas sparging performances of a flat sheet and tubular polymeric membranes were investigated in 3.1 m bubble column bioreactor operated in a semi batch mode. Air–water and air–CMC (Carboxymethyl cellulose) solutions of 0.5, 0.75 and 1.0 % w/w were used as interacting gas–liquid mediums. CMC solutions were employed in the study to simulate rheological properties of bioreactor broth. Gas holdup, bubble size distribution, interfacial area and gas–liquid mass transfer were studied in the homogeneous bubbly flow hydrodynamic regime with superficial gas velocity (U _G) range of 0.0004–0.0025 m/s. The study indicated that the tubular membrane sparger produced the highest gas holdup and densely populated fine bubbles with narrow size distribution. An increase in liquid viscosity promoted a shift in bubble size distribution to large stable bubbles and smaller specific interfacial area. The tubular membrane sparger achieved greater interfacial area and an enhanced overall mass transfer coefficient (K _La) by a factor of 1.2–1.9 compared to the flat sheet membrane.     

Cooling vest worn during active warm-up improves 5-km run performance in the heat.

We investigated whether a cooling vest worn during an active warm-up enhances 5-km run time in the heat. Seventeen competitive runners (9 men, maximal oxygen uptake = 66.7 +/- 5.9 ml x kg(-1) x min(-1); 8 women, maximal oxygen uptake = 58.0 +/- 3.2 ml x kg(-1) x min(-1)) completed two simulated 5-km runs on a treadmill after a 38-min active warm-up during which they wore either a T-shirt (C) or a vest filled with ice (V) in a hot, humid environment (32 degrees C, 50% relative humidity). Wearing the cooling vest during warm-up significantly (P < 0.05) blunted increases in body temperature, heart rate (HR), and perception of thermal discomfort during warm-up compared with control. At the start of the 5-km run, esophageal, rectal, mean skin, and mean body temperatures averaged 0.3, 0.2, 1.8, and 0.4 degrees C lower; HR averaged 11 beats/min lower; and perception of thermal discomfort (5-point scale) averaged 0.6 point lower in V than C. Most of these differences were eliminated during the first 3.2 km of the run, and these variables were not different at the end. The 5-km run time was significantly lower (P < 0.05) by 13 s in V than C, with a faster pace most evident during the last two-thirds of the run. We conclude that a cooling vest worn during active warm-up by track athletes enhances 5-km run performance in the heat. Reduced thermal and cardiovascular strain and perception of thermal discomfort in the early portion of the run appear to permit a faster pace later in the run.     

Expression of endothelial selectin ligands on human leukocytes following dive

The fact that impaired endothelial-dependent vasodilatation after scuba diving often occurs without visible changes in the endothelial layer implies its biochemical origin. Since Lewis x (CD15) and sialyl-Lewis x (CD15s) are granulocyte and monocyte carbohydrate antigens recognized as ligands by endothelial selectins, we assumed that they could be sensitive markers for impaired vasodilatation following diving. Using flow cytometry, we determined the CD15 and CD15s peripheral blood mononuclear cells of eight divers, 30 mins before and 50 mins after a single dive to 54 m for 20 mins bottom time. The number of gas bubbles in the right heart was monitored by ultrasound. Gas bubbles were seen in all eight divers, with the average number of bubbles/cm(2) 1.9 +/- 1.9. The proportion of CD15 + monocytes increased 2-fold after the dive as well as the subpopulation of monocytes highly expressing CD15s. The absolute number of monocytes was slightly, but not significantly, increased after the dive, whereas the absolute number of granulocytes was markedly elevated (up to 61%). There were no significant correlations between bubble formation and CD15 + monocyte expression (r = - 0.56; P = 0.17), as well as with monocytes highly expressing CD15s (r = 0.43; P = 0.29). This study suggests that biochemical changes induced by scuba diving primarily activate existing monocytes rather than increase the number of monocytes at a time of acute arterial endothelial dysfunction.     

The effects of hyperthermia and hypoxia on ventilation during low-intensity steady-state exercise

This study assessed whether the elevated sensitivity of ventilation to hypoxia during exercise is accounted for by an elevation of esophageal temperature (T(es)). Eleven males volunteered for two exercise sessions on an underwater, head-out cycle ergometer at a steady-state rate of oxygen consumption (V(.)(O(2))) of approximately 0.87 l/min (SD 0.07). In one exercise session, 31.5 degrees C (SD 1.4) water held T(es) at a normothermic level of approximately 37.1 degrees C, and in the other exercise session, water at 38.2 degrees C (SD 0.1) maintained a hyperthermic T(es) of approximately 38.5 degrees C. After a 30-min rest and 20-min warm-up, exercising participants inhaled air for 10 min [Euoxia 1 (E1)], an isocapnic hypoxic gas mixture with 12% O(2) in N(2) (H1) for the next 10 min and air again [Euoxia 2 (E2)] for the last 10 min. A significant increase in V(.)(E) during all hyperthermia conditions (0.01< P < 0.048) was evident; however, during hyperthermic hypoxia, there was a disproportionate and significant (P = 0.017) increase in V(.)(E) relative to normothermic hypoxia. This was the main explanation for a significant esophageal temperature and gas type interaction (P = 0.012) for V(.)(E). Significant effects of hyperthermia, isocapnic hypoxia, and their positive interaction remained evident after removing the influence of (V(.)(O(2))) on V(.)(E). Serum lactate and potassium concentrations, as well as hemoglobin oxygen saturation, were each not significantly different between normothermic and hyperthermic-hypoxic conditions. In conclusion, the elevated sensitivity of exercise ventilation to hypoxia during exertion appears to be modulated by elevations in esophageal temperature, potentially because of a temperature-mediated stimulation of the peripheral chemoreceptors.     

Mechanical compression affecting the thermal-induced conformational stability and denaturation temperature of human fibrinogen

Thermal-induced conformational stability and changes in denaturation temperature of human fibrinogen (FBG) after different mechanical compressions were investigated by a simultaneous Fourier transform infrared microspectroscopy equipped with thermal analyzer (thermal FTIR microscopic system). The confocal Raman microspectroscopy was also applied to determine the thermal reversibility of solid FBG. FBG powder was pressed on one KBr pellet (1 KBr method) or sealed within two KBr pellets (2 KBr method) by different mechanical compressions. The result indicates that there was no marked difference in the thermal behavior for the solid FBG samples prepared by 1 KBr method in the heating process even under different mechanical compression pressures, in which the thermal-induced denaturation temperatures from native to denatured state were maintained constant at 66-67 degrees C. However, the denaturation temperature for the solid FBG samples prepared by 2 KBr method was shifted from 55 to 62 degrees C with the increase of mechanical compression pressure. A good linear correlation was also found between the denaturation temperature and mechanical compression pressure for FBG samples prepared by 2 KBr method. The solid FBG sample, whether prepared by 1 KBr or 2 KBr method, was also found to show the thermal-irreversible property.     

Intracellular gas supersaturation tolerances of erythrocytes and resealed ghosts.

Intact mammalian, avian, and amphibian erythrocytes were saturated with up to 300 atm nitrogen or argon gas and rapidly decompressed. Despite the profuse nucleation of gas bubbles in the suspending fluid, no evidence of intracellular gas bubble nucleation was found; all or most of the cells remained intact and little or no hemoglobin escaped. Internal bubbles were similarly absent from resealed ghosts of human erythrocytes as shown by lack of disintegration and by retention of an entrapped fluorescent compound. The absence of bubbles may indicate that much of the internal water does not have the same nucleation properties as external water.     

Impact of a single session of intermittent pneumatic leg compressions on skeletal muscle and isolated artery gene expression in rats

Intermittent pneumatic leg compressions (IPC) have proven to be an effective noninvasive approach for treatment of patients with claudication, but the mechanisms underlying the clinical benefits remain elusive. In the present study, a rodent model of claudication produced by bilateral ligation of the femoral artery was used to investigate the acute impact of a single session of IPC (150 min) on hemodynamics, skeletal muscle (tibialis anterior), and isolated collateral artery (perforating artery) expression of a subset of genes associated with inflammation and vascular remodeling. In addition, the effect of compression frequency (15 vs. 3 compressions/min) on the expression of these factors was studied. In ligated animals, IPC evoked an increase of monocyte chemoattractant protein-1 (MCP-1) and cytokine-induced neutrophil chemoattractant 1 (CXCL1) mRNA (P < 0.01) and immunostaining (P < 0.05), as well as a minor increase in VEGF immunostaining in the muscle endomysium 150 min postintervention. Further, collateral arteries from these animals showed an increased expression of MCP-1 (approximately twofold, P = 0.02). These effects were most evident in the group exposed to the high-frequency protocol (15 compressions/min). In contrast, IPC in sham-operated control animals evoked a modest initial upregulation of VEGF (P = 0.01), MCP-1 (P = 0.02), and CXCL1 (P = 0.03) mRNA in the muscle without concomitant changes in protein levels. No changes in gene expression were observed in arteries isolated from sham animals. In conclusion, IPC acutely up-regulates the expression of important factors involved in vascular remodeling in the compressed muscle and collateral arteries in a model of hindlimb ischemia. These effects appear to be dependent on the compression frequency, such that a high compression frequency (15 compressions/min) evokes more consistent and robust effects compared with the frequency commonly employed clinically to treat patients with claudication (3 compressions/min).     

Pulmonary Surfactant Protein SP-C Counteracts the Deleterious Effects of Cholesterol on the Activity of Surfactant Films under Physiologically Relevant Compression-Expansion Dynamics

The presence of cholesterol is critical in defining a dynamic lateral structure in pulmonary surfactant membranes. However, an excess of cholesterol has been associated with impaired surface activity of surfactant. It has also been reported that surfactant protein SP-C interacts with cholesterol in lipid/protein interfacial films. In this study, we analyzed the effect of SP-C on the thermodynamic properties of phospholipid membranes containing cholesterol, and the ability of lipid/protein complexes containing cholesterol to form and respread interfacial films capable of producing very low surface tensions upon repetitive compression-expansion cycling. SP-C modulates the effect of cholesterol to reduce the enthalpy associated with the gel-to-liquid-crystalline melting transition in dipalmitoylphosphatidylcholine (DPPC) bilayers, as analyzed by differential scanning calorimetry. The presence of SP-C affects more subtly the effects of cholesterol on the thermotropic properties of ternary membranes, mimicking more closely the lipid composition of native surfactant, where SP-C facilitates the miscibility of the sterol. Incorporation of 1% or 2% SP-C (protein/phospholipid by weight) promotes almost instantaneous adsorption of suspensions of DPPC/palmitoyloleoylphospatidylcholine (POPC)/palmitoyloleoyl-phosphatidylglycerol (POPG) (50:25:15, w/w/w) into the air-liquid interface of a captive bubble, in both the absence and presence of cholesterol. However, cholesterol impairs the ability of SP-C-containing films to achieve very low surface tensions in bubbles subjected to compression-expansion cycling. Cholesterol also substantially impairs the ability of DPPC/POPC/POPG films containing 1% surfactant protein SP-B to mimic the interfacial behavior of native surfactant films, which are characterized by very low minimum surface tensions with only limited area change during compression and practically no compression-expansion hysteresis. However, the simultaneous presence of 2% SP-C practically restores the compression-expansion dynamics of cholesterol- and SP-B-containing films to the efficient behavior shown in the absence of cholesterol. This suggests that cooperation between the two proteins is required for lipid-protein films containing cholesterol to achieve optimal performance under physiologically relevant compression-expansion dynamics.     

Effect of body temperature during exercise on skeletal muscle cytochrome c oxidase content.

This study determined the role of body temperature during exercise on cytochrome-c oxidase (CytOx) activity, a marker of mitochondrial content, and mitochondrial heat shock protein 70 (mtHSP70), which is required for import of nuclear-coded preproteins. Male, 10-wk-old, Sprague-Dawley rats exercised identically for 9 wk in ambient temperatures of 23 degrees C (n = 10), 8 degrees C with wetted fur (n = 8), and 4 degrees C with wetted fur and fan (n = 7). These conditions maintained exercising core temperature (T(c)) at 40.4, 39.2, or 38.0 degrees C (resting temperature), respectively. During weeks 3-9, exercisers ran 5 days/wk up a 6% grade at 20 m/min for 60 min. Animals were housed at 23 degrees C. Gastrocnemius CytOx activity in T(c)=38.0 degrees C (83.5 +/- 5.5 microatoms O x min(-1) x g wet wt(-1)) was greater than all other groups (P < 0.05), exceeding sedentary (n = 7) by 73.2%. T(c) of 40.4 and 39.2 degrees C also were higher than sedentary by 22.4 and 37.4%, respectively (P < 0.05). Quantification of CytOx content verified that the increased activity was due to an increase in protein content. In extensor digitorum longus, a nonactive muscle, CytOx was not elevated in T(c) = 38.0 degrees C. mtHSP70 was significantly elevated in gastrocnemius of T(c) = 38.0 degrees C compared with sedentary (P < 0.05) but was not elevated in extensor digitorum longus (P > 0.05). The data indicate that decreasing exercise T(c) may enhance mitochondrial biogenesis and that mtHSP70 expression is not dependent on temperature.