Temperature dependent behavior of the canine medial collateral ligament

The temperature dependent tensile behavior of ligament was investigated from 2 degrees C to 37 degrees C. Nondestructive cyclic tests were performed on ten canine femur-medial collateral ligament-tibia (FMT) complexes at sequential temperatures of 22 degrees C, 22 degrees C, 27 degrees C, 32 degrees C, 37 degrees C, and again at 22 degrees C. The samples were rested at zero load between tests for sufficient time periods to allow for full recovery from the ligament's time and history dependent viscoelastic properties. Ten additional FMT complexes were sequentially tested in a similar fashion, but at temperatures of 22 degrees C, 22 degrees C, 2 degrees C, 6 degrees C, 14 degrees C, and 22 degrees C. All canine FMT complexes showed temperature dependent viscoelastic properties: the measured area of hysteresis decreased with increasing temperature; the cyclic load relaxation behavior plateaued to a higher value at lower temperatures; and the tensile load at a predetermined ligament substance strain level had an inversely proportional relationship with respect to temperature.     

Investigation of the Drug Release and Surface Morphological Properties of Film-Coated Pellets, and Physical, Thermal and Mechanical Properties of Free Films as a Function of Various Curing Conditions

The purpose of the present investigation was to elucidate the influence of curing on different physical properties of Eudragit NE and RS coating systems. Increased curing times resulted in decreased drug release rates from Eudragit NE-coated beads. However, an increase in drug release rates was noticed at longer curing times and higher temperatures for the Eudragit RS coating system. The surface morphological changes of the film-coated beads revealed that there were no visible macroscopic changes as a result of curing. The absence of any ibuprofen melting peak in the DSC thermograms of cured NE and RS coated beads confirmed that there was no surface crystallization of ibuprofen. These results indicated that the increase in drug release rates from RS coated pellets, when subjected to long curing times, resulted from loss of plasticizer. Free films of Eudragit NE exhibited an increase in tensile strength with increased curing times, whereas Eudragit RS free films showed a decrease in tensile strength beyond 4 h of curing at 70 and 90 degrees C. The film thicknesses and weights of free films of Eudragit RS prepared with triethyl citrate plasticizer were found to change more dramatically with curing than did free films of Eudragit RS prepared with ibuprofen as the plasticizer. An increase in pore volume was also observed with increased curing times for Eudragit RS free films. Such changes with curing were shown to be due to the loss of plasticizer molecules, leading to the formation of molecular-scale voids and channels.     

The effects of low temperatures on intracellular transport of newly synthesized albumin and haptoglobin in rat hepatocytes.

Isolated rat hepatocytes were pulse-labelled with [35S]methionine at 37 degrees C and subsequently incubated (chased) for different periods of time at different temperatures (37-16 degrees C). The time courses for the secretion of [35S]methionine-labelled albumin and haptoglobin were determined by quantitative immunoprecipitation of the detergent-solubilized cells and of the chase media. Both proteins appeared in the chase medium only after a lag period, the length of which increased markedly with decreasing chase temperature: from about 10 and 20 min at 37 degrees C to about 60 and 120 min at 20 degrees C for albumin and haptoglobin respectively. The rates at which the proteins were externalized after the lag period were also strongly affected by temperature, the half-time for secretion being 20 min at 37 degrees C and 200 min at 20 degrees C for albumin; at 16 degrees C no secretion could be detected after incubation for 270 min. Analysis by subcellular fractionation showed that part of the lag occurred in the endoplasmic reticulum and that the rate of transfer to the Golgi complex was very temperature-dependent. The maximum amount of the two pulse-labelled proteins in Golgi fractions prepared from cells after different times of chase decreased with decreasing incubation temperatures, indicating that the transport from the Golgi complex to the cell surface was less affected by low temperatures than was the transport from the endoplasmic reticulum to the Golgi complex.     

Effect of temperature on the structure of trout troponin C

Adaptation for life at different temperatures can cause changes in many aspects of an organism. One example is the expression of different protein isoforms in species adapted to different temperatures. The calcium regulatory protein cardiac troponin C (cTnC), from rainbow trout (Oncorhynchus mykiss), is a good model for studying temperature effects, both because of its low physiological temperature and because mammalian cTnC, extensively studied at higher temperatures, can be used for comparison. We determined the structure and studied the backbone dynamics of the regulatory domain of trout cardiac troponin C (ScNTnC) with one Ca(2+) bound at 7 and 30 degrees C, using nuclear magnetic resonance spectroscopy (NMR). The overall fold of the regulatory domain of trout cTnC at both temperatures is similar to the regulatory domain of mammalian (human, bovine, and porcine isoform) cTnC bound to one Ca(2+). By comparing the trout structures at the two temperatures, we identify differences between the positions of the helices flanking the calcium binding loops, and the overall structure at 7 degrees C is more compact than that at 30 degrees C. The structure at 7 degrees C is more similar to the mammalian cTnC, which was determined at 30 degrees C, indicating that they have the same conformation at their respective physiological temperatures. The dynamic properties of the regulatory domain of trout cTnC are similar at the two temperatures that were used in these studies.     

Transport and tensile properties of compression-molded wheat gluten films

Mechanical and transport properties were assessed on wheat gluten films with a glycerol content of 25-40%, prepared by compression molding for 5-15 min at temperatures between 90 and 130 degrees C. Effects of storing the films up to 24 days, in 0 and 50% relative humidity (RH), were assessed by tensile measurements. The films were analyzed with respect to methanol zero-concentration diffusivity, oxygen permeability (OP), water vapor permeability (WVP), Cobb60 and sodium dodecyl sulfate (SDS) solubility coupled with sonication. The SDS solubility and methanol diffusivity were lower at the higher molding temperature. Higher glycerol content resulted in higher OP (90-95% RH), WVP, and Cobb60 values, due to the plasticizing and hygroscopic effects. Higher glycerol contents gave a lower fracture stress, lower Young's modulus, lower fracture strain, and less strain hardening. The mold time had less effect on the mechanical properties than mold temperature and glycerol content. The fracture stress and Young's modulus increased and the fracture strain decreased with decreasing moisture content.     

Factors affecting the freeze-fracture morphology of in vivo polyhydroxyalkanoate granules

Interesting morphologies were observed when Comamonas acidovorans containing polyhydroxyalkanoates (PHA) of various compositions was freeze-fractured at temperatures far below the glass transition temperatures of PHA. In vivo granules of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) comparatively showed the most ductility, and could be stretched extensively. Contrary to the uniform needle-type deformation shown by the poly(3-hydroxybutyrate) homopolymer when fractured at -110 degrees C, copolymers containing 3-hydroxyvalerate units showed various deformation structures. Similar observations were made when in vivo granules of poly(3-hydroxybutyrate-co-4-hydroxybutyrate) were freeze-fractured, although the ductility of the latter was much reduced. In addition, it was found that fracturing at -160 degrees C resulted in decreased ductility of the PHA granules with the concomitant increase in the number of mushroom-type deformation structures. Our results suggest that PHA granules with higher resistance to freeze-fracture deformation show less ductility, and therefore produce the mushroom-type morphology. This is the first report on the freeze-fracture morphology of PHA copolymers containing short-chain-length monomers.     

Behavioral thermoregulation in Hemigrapsus nudus,the amphibious purple shore crab

The thermoregulatory behavior of Hemigrapsus nudus, the amphibious purple shore crab, was examined in both aquatic and aerial environments. Crabs warmed and cooled more rapidly in water than in air. Acclimation in water of 16 degrees C (summer temperatures) raised the critical thermal maximum temperature (CTMax); acclimation in water of 10 degrees C (winter temperatures) lowered the critical thermal minimum temperature (CTMin). The changes occurred in both water and air. However, these survival regimes did not reflect the thermal preferences of the animals. In water, the thermal preference of crabs acclimated to 16 degrees C was 14.6 degrees C, and they avoided water warmer than 25.5 degrees C. These values were significantly lower than those of the crabs acclimated to 10 degrees C; these animals demonstrated temperature preferences for water that was 17 degrees C, and they avoided water that was warmer than 26.9 degrees C. This temperature preference was also exhibited in air, where 10 degrees C acclimated crabs exited from under rocks at a temperature that was 3.2 degrees C higher than that at which the 16 degrees C acclimated animals responded. This behavioral pattern was possibly due to a decreased thermal tolerance of 16 degrees C acclimated crabs, related with the molting process. H. nudus was better able to survive prolonged exposure to cold temperatures than to warm temperatures, and there was a trend towards lower exit temperatures with the lower acclimation (10 degrees C) temperature. Using a complex series of behaviors, the crabs were able to precisely control body temperature independent of the medium, by shuttling between air and water. The time spent in either air or water was influenced more strongly by the temperature than by the medium. In the field, this species may experience ranges in temperatures of up to 20 degrees C; however, it is able to utilize thermal microhabitats underneath rocks to maintain its body temperature within fairly narrow limits.     

Effect of ambient temperatures during oocyte recovery on in vitro production of bovine embryos

Recovery of oocytes from ovaries collected at slaughter was carried out at three ambient temperatures (25 degrees, 30 degrees and 35 degrees C) to assess the effect on subsequent embryonic production in vitro. Oocytes recovered at each temperature were thereafter maintained at temperatures > or =35 degrees C as they were subjected to in vitro maturation, fertilization and culture (IVM/IVF/IVC). The oocytes and resulting embryos within each temperature group were subsequently evaluated for their rates of fertilization, cleavage and development to blastocysts, as well as for the number of cells/blastocyst. The results demonstrate that exposure of cumulus-ocyte-complexes (COCs) to temperatures below 35 degrees C during oocyte recovery is detrimental to optimal embryo production. Although the fertilization and cleavage rates of oocytes recovered at temperatures below 35 degrees C were not significantly lower than that of the controls, the percentage of oocytes recovered at 35 degrees C that developed to the blastocyst stage following fertilization and culture (33.7%) was significantly greater than those from oocytes recovered at either 25 degrees C (22.4%) or 30 degrees C (19.5%). The mean numbers of blastomeres/embryo were significantly lower in embryos derived from oocytes collected at either 25 degrees or 30 degrees compared with those collected at 35 degrees C. The results of this study suggest that exposure of COCs to temperatures below 35 degrees C during oocyte recovery may significantly decrease both the quantity and quality of embryos produced by in vitro methods.     

Endoglucanase-producing fungi isolated from Cape Evans historic expedition hut on Ross Island, Antarctica

Early explorers of Antarctica's Heroic Era erected wooden buildings and brought large quantities of supplies to survive in Antarctica. The introduction of wood and other organic materials provided nutrient sources for fungi that were indigenous to Antarctica or were brought in with the materials and adapted to the harsh conditions. Seventy-two isolates of filamentous fungi were cultured on selective media from interior structural wood of the Cape Evans historic hut and 27 of these screened positive for the ability to degrade carboxymethyl cellulose (CMC). Four non-CMC-degrading isolates were added to a group of 14 CMC-degrading isolates for further study, and endo-1, 4-beta-glucanase activity was demonstrated in the extracellular supernatant from all of these 18 isolates when grown at 4 degrees C, and also when they were grown at 15 degrees C. Isolates of Penicillium roquefortii and Cadophora malorum showed preference for growth at 15 degrees C rather than 25 degrees C or 4 degrees C indicating psychrotrophic characteristics. These results demonstrate that cellulolytic filamentous fungi found in Antarctica are capable of growth at cold temperatures and possess the ability to produce extracellular endo-1, 4-beta-glucanase when cultured at cold and temperate temperatures.     

Influence of temperature on growth rate and competition between two psychrotolerant Antarctic bacteria: low temperature diminishes affinity for substrate uptake.

The growth kinetics of two psychrotolerant Antarctic bacteria, Hydrogenophaga pseudoflava CR3/2/10 (2/10) and Brevibacterium sp. strain CR3/1/15 (1/15), were examined over a range of temperatures in both batch culture and glycerol-limited chemostat cultures. The maximum specific growth rate (mu max) and Ks values for both bacteria were functions of temperature, although the cell yields were relatively constant with respect to temperature. The mu max values of both strains increased up to an optimum temperature, 24 degrees C for 2/10 and 20 degrees C for 1/15. Strain 1/15 might therefore be considered to be more psychrophilic than strain 2/10. For both bacteria, the specific affinity (mu max/Ks) for glycerol uptake was lower at 2 than at 16 degrees C, indicating a greater tendency to substrate limitation at low temperature. As the temperature increased from 2 to 16 degrees C, the specific affinity of 1/15 for glycerol increased more rapidly than it did for 2/10. Thus 1/15, on the basis of this criterion, was less psychrophilic than was 2/10. The steady-state growth kinetics of the two strains at 2 and 16 degrees C imply that 1/15 would be able to outgrow 2/10 only at relatively low substrate concentrations (< 0.32 g of glycerol.liter-1) and high temperatures (> 12 degrees C), which suggests that 1/15 has a less psychrotolerant survival strategy than does 2/10. Our data were compared with other data in the literature for bacteria growing at low temperatures. They also showed an increase of substrate-specific affinity with increasing temperature.(ABSTRACT TRUNCATED AT 250 WORDS)     

Heat-shock responses in two leguminous plants: a comparative study

Relative growth rates, basal and acclimated thermotolerance, membrane damage, fluorescence emission, and relative levels of free and conjugated ubiquitin and HSP70 were compared after 2 h of treatment at different temperatures between Prosopis chilensis and Glycine max (soybean), cv. McCall, to evaluate if the thermotolerance of these two plants was related to levels of accumulation of heat shock proteins. Seedlings of P. chilensis germinated at 25 degrees C and at 35 degrees C and grown at temperatures above germination temperature showed higher relative growth than soybean seedlings treated under the same conditions. The lethal temperature of both species was 50 degrees C after germination at 25 degrees C. However, they were able to grow at 50 degrees C after germination at 35 degrees C. Membrane damage determinations in leaves showed that P. chilensis has an LT(50) 6 degrees C higher than that of soybean. There were no differences in the quantum yield of photosynthesis (F(v)/F(m)), between both plants when the temperatures were raised. P. chilensis showed higher relative levels of free ubiquitin, conjugated ubiquitin and HSP70 than soybean seedlings when the temperatures were raised. Time-course studies of accumulation of these proteins performed at 40 degrees C showed that the relative accumulation rates of ubiquitin, conjugated ubiquitin and HSP70 were higher in P. chilensis than in soybean. In both plants, free ubiquitin decreased during the first 5 min and increased after 30 min of heat shock, conjugated ubiquitin increased after 30 min and HSP70 began to increase dramatically after 20 min of heat shock. From these data it is concluded that P. chilensis is more tolerant to acute heat stress than soybean.     

Enzymatic desorption of layer-by-layer assembled multilayer films and effects on the release of encapsulated indomethacin microcrystals

Polyelectrolyte multilayer films were prepared through layer-by-layer (LbL) self-assembly of chitosan (CHI) and pyrene labeled poly(2-acrylamido-2-methylpropanesulfonic acid) (APy). After incubation in an enzyme pepsin solution, multilayer films were partially destroyed as detected by a decrease in fluorescence intensity due to enzymatic degradation of CHI and desorption of APy. The multilayer desorption rate was the highest at pH 4.0. Increasing temperature from 20 degrees C to 60 degrees C accelerated desorption. The enzymatic desorption was also observed from microcapsule walls made of CHI/alginate (ALG) multilayer films directly deposited on indomethacin (IDM) microcrystals by LbL self-assembly. After pepsin erosion, the IDM release from the microcapsule monitored by UV absorbance was obviously accelerated due to desorption. The influence of incubation time, pH, and temperature of the pepsin solution on the IDM release was investigated. The release rate was the fastest after incubation in the pepsin solution at pH 4.0 due to the highest activity of pepsin. Increasing incubation temperature from 20 degrees C to 60 degrees C, however, slowed down the release rate, which was considered to be due to the formation of more perfect and compact multilayer films through the chain rearrangement at higher temperatures. The CHI/ALG multilayer film was found to maintain its barrier function to the IDM diffusion even after 6-h incubation in the pepsin solution.     

Flexible chitin films: structural studies

Chitin gels were transformed into thin, flexible chitin films with minimal dimensional shrinkage and maximum flexibility and thickness in the range of 25-80 microm by a cold-press process. Solvent residue was removed by heating the films at 50 degrees C for 12 h, followed by rinsing in 95% ethanol. The crystallinity and mechanical properties of the flexible chitin films were found to be a function of the amount of shrinkage from the gel to the final film that was obtained. For 28-microm thick films with 30% shrinkage, transparency of up to 90% was found. X-ray diffractometry (XRD) showed that the number of diffraction peaks appearing at 2theta;=23 degrees and 2theta;=27 degrees became increasingly sharper with shrinkage. Topographical information obtained from scanning electron microscopy (SEM) and atomic force microscopy (AFM) attributed the structural morphology of the films to the formation of sub-microscopic micelles. Scanning transmission electron microscopy (STEM) showed that shrinkage resulted in coarser microstructure, affecting tensile properties, where the ductility and toughness were proportional to the amount of shrinkage. These flexible chitin films have potential as wound dressing materials.     

Water-induced hydrophobicity of soy protein materials containing 2,2-diphenyl-2-hydroxyethanoic acid

Biodegradable soy protein isolate (SPI), containing 2,2-diphenyl-2-hydroxyethanoic acid, films (SB) were successfully prepared with bis-(2-hydroxyethyl)sulfide as a plasticizer by compression molding at 155 degrees C and 15 MPa. By immersing the SB in distilled water for 26 h, we prepared the films (coded as SB-WM) having good water resistance. The films were characterized by Fourier transform infrared spectroscopy, scanning electron microscopy, thermogravimetric analysis, dynamic mechanical thermal analysis, and tensile testing to evaluate their structure and properties. Moreover, the surface of the SB-WM films was analyzed by X-ray photoelectron spectroscopy and contact angle measurement. SB-WM films exhibited significantly higher contact angle than SB. The results revealed that a lotus-like nanoscale structure was created in SB-WM films, with increased hydrophobicity, through the process of the solvent-induced microphase separation during the immersion in water. More stable compound diphenylhydroxymethane could form from 2,2-diphenyl-2-hydroxyethanoic acid of SB in water, leading to the hydrophobicity of the SB-WM materials. A "green" and easy method for fabricating hydrophobic materials from soy protein has been provided in this work.     

Thermoregulation by kangaroos from mesic and arid habitats: influence of temperature on routes of heat loss in eastern grey kangaroos (Macropus giganteus) and red kangaroos (Macropus rufus)

We examined thermoregulation in red kangaroos (Macropus rufus) from deserts and in eastern grey kangaroos (Macropus giganteus) from mesic forests/woodlands. Desert kangaroos have complex evaporative heat loss mechanisms, but the relative importance of these mechanisms is unclear. Little is known of the abilities of grey kangaroos. Our detailed study of these kangaroos' thermoregulatory responses at air temperatures (T(a)) from -5 degrees to 45 degrees C showed that, while some differences occur, their abilities are fundamentally similar. Both species show the basic marsupial characteristics of relatively low basal metabolism and body temperature (T(b)). Within the thermoneutral zone, T(b) was 36.3 degrees + or - 0.1 degrees C (X + or - SE) in both species, and except for a small rise at T(a) 45 degrees C, T(b) was stable over a wide range of T(a). Metabolic heat production was 25% higher in red kangaroos at T(a) -5 degrees C. At the highest T(a) (45 degrees C), both species relied on evaporative heat loss (EHL) to maintain T(b); both panting and licking were used. The eastern grey kangaroo utilised panting (76% of EHL) as the principal mode of EHL, and while this was so for red kangaroos, cutaneous evaporative heat loss (CEHL) was significant (40% of EHL). CEHL appeared to be mainly licking, as evidenced from surface temperatures. Both species utilised peripheral vascular adjustments to control heat flow, as indicated by changes in dry conductance (C(dry)). At lower temperatures, C(dry) was minimal, but it increased significantly at T(a) just below T(b) (33 degrees C); in these conditions, the C(dry) of red kangaroos was significantly higher than that of eastern grey kangaroos, indicating a greater reliance on dry heat loss. Under conditions where heat flows into the body from the environment (T(a) 45 degrees C), there was peripheral vasoconstriction to reduce this inflow; C(dry) decreased significantly from the values seen at 33 degrees C in both kangaroos. The results indicated that, while both species have excellent thermoregulatory abilities, the desert red kangaroos may cope better with more extreme temperatures, given that they respond to T(a) 45 degrees C with lower respiratory evaporation than do the eastern grey kangaroos.     

A true summer diapause induced by high temperatures in the cotton bollworm, Helicoverpa armigera (Lepidoptera: Noctuidae)

Summer diapause in the cotton bollworm, Helicoverpa armigera (Hübner), which prolongs the pupal stage, particularly in males, is induced by high temperatures. In the laboratory, summer-diapausing pupae of H. armigera were induced at high temperatures (33-39 degrees C) with a photoperiod of LD8:16; winter-diapausing and non-diapausing pupae, cultured at 20 degrees C with a photoperiod of LD8:16 and at 27 degrees C, LD16:8, respectively, acted as a control. Retention time of eye spots, weight, and lipid and glycogen levels were compared. At high temperatures, both body weight and energy storage capacity were much higher in summer-diapausing pupae than in non-diapausing pupae reared at 33-39 degrees C. At temperatures (>33 degrees C) high enough to maintain summer diapause, the eye spots of summer-diapausing pupae did not move during the 30-day experiment. However, eye spots of summer-diapausing pupae placed at 30 degrees C began to move about 10 days after they were transferred, significantly later than in non-diapausing pupae reared at 33-39 degrees C or non-diapausing pupae reared at 27 degrees C, which initiated eye spot movement 2 days after pupation. The differences in retention time of eye spots between summer- and winter-diapausing pupae shows that winter diapause is more intense than summer diapause in this insect. The weight loss, and lipid and glycogen metabolism curves indicate that the summer-diapausing pupae's metabolism is very low. We conclude that summer diapause in the cotton bollworm is a true diapause and that the summer diapause enables the cotton bollworm to withstand the high temperatures of summer.     

Growth temperature regulation of host-specific modifications of rhizobial lipo-chitin oligosaccharides: the function of nodX is temperature regulated

Lipo-chitin oligosaccharides (LCOs) are usually produced and isolated for structural analysis from bacteria cultured under laboratory rather than field conditions. We have studied the influence of bacterial growth temperature on the LCO structures produced by different Rhizobium leguminosarum strains, using thin-layer chromatographic, high-performance liquid chromatographic, and mass spectrometric analyses. Wild-type R. leguminosarum bv. viciae A1 was shown to produce larger relative amounts of nodX-mediated, acetylated LCOs at 12 degrees C than at 28 degrees C, indicating that the activity of nodX (a gene encoding an LCO O-acetyl transferase) is temperature dependent. Interestingly, symbiotic resistance genes sym1 and sym2 found in primitive pea cultivars are also temperature sensitive, only being active at low temperatures, at which they block nodulation by R. leguminosarum bv. viciae strains lacking nodX. We therefore propose that the gene-for-gene relationship between plant and bacterium has a temperature-sensitive mechanism as an adaptation to environmental conditions. An R. leguminosarum bv. trifolii strain was also shown to produce larger relative amounts of nodX-mediated, acetylated LCOs at 12 degrees C than at 28 degrees C. The major components synthesized by the two strains are produced at both temperatures but in different relative amounts, while some minor components are only produced at one of the two temperatures.     

Sphingomyelin interfacial behavior: the impact of changing acyl chain composition

Sphingomyelins (SMs) containing homogeneous acyl chains with 12, 14, 16, 18, 24, or 26 carbons were synthesized and characterized using an automated Langmuir-type film balance. Surface pressure was monitored as a function of lipid molecular area at constant temperatures between 10 degrees C and 30 degrees C. SM containing lauroyl (12:0) acyl chains displayed only liquid-expanded behavior. Increasing the length of the saturated acyl chain (e.g., 14:0, 16:0, or 18:0) resulted in liquid-expanded to condensed two-dimensional phase transitions at many temperatures in the 10-30 degrees C range. Similar behavior was observed for SMs with lignoceroyl (24:0) or (cerotoyl) 26:0 acyl chains, but isotherms showed only condensed behavior at 10 and 15 degrees C. Insights into the physico-mechanical in-plane interactions occurring within the different SM phases and accompanying changes in SM phase state were provided by analyzing the interfacial area compressibility moduli. At similar surface pressures, SM fluid phases were less compressible than those of phosphatidylcholines with similar chain structures. The area per molecule and compressibility of SM condensed phases depended upon the length of the saturated acyl chain and upon spreading temperature. Spreading of SMs with very long saturated acyl chains at temperatures 30-35 degrees below T(m) resulted in condensed films with lower in-plane compressibilities, but consistently larger cross-sectional molecular areas than the condensed phases achieved by spreading at temperatures only 10-20 degrees below T(m). This behavior is discussed in terms of the enhancement of SM lateral aggregation by temperature reduction, a common approach used during domain isolation from biomembranes.     

Metabolism, body temperature and thermal conductance of fruit-doves (Aves: Columbidae, Treroninae)

Basal metabolic rate (MR), body temperature (T(b)) and wet thermal conductance (C(wet)) of three tropical species of fruit-doves were investigated at ambient temperatures (T(a)) of 11-33 degrees C in activity (alpha) and rest (rho) phases to investigate the possible effect of obligate frugivory on the physiology of columbids. The basal metabolic rates of Ptilinopus melanospila (black-naped fruit-dove, 94 g), Drepanoptila holosericea (cloven-feathered dove, 198 g) and Ducula pinon (Pinon's imperial pigeon, 748 g) are 20-38% lower than predicted for all birds, including granivorous columbid species from temperate and tropical regions. The MR was minimal at a T(a) value of approximately 30 degrees C (=lower critical temperature, T(lc)) for all three species, indicating that these rainforest birds are not able to withstand high ambient temperatures as well as arid-adapted members of the pigeon family. Minimal wet-thermal conductance was, on average, higher than expected, indicating poor insulation in these tropical birds. Body temperatures were as expected; however, below T(lc) the body temperatures decreased to levels of 35-36 degrees C (T(a)=12 degrees C).     

The melting of pulmonary surfactant monolayers.

Monomolecular films of phospholipids in the liquid-expanded (LE) phase after supercompression to high surface pressures (pi), well above the equilibrium surface pressure (pi(e)) at which fluid films collapse from the interface to form a three-dimensional bulk phase, and in the tilted-condensed (TC) phase both replicate the resistance to collapse that is characteristic of alveolar films in the lungs. To provide the basis for determining which film is present in the alveolus, we measured the melting characteristics of monolayers containing TC dipalmitoyl phosphatidylcholine (DPPC), as well as supercompressed 1-palmitoyl-2-oleoyl phosphatidylcholine and calf lung surfactant extract (CLSE). Films generated by appropriate manipulations on a captive bubble were heated from < or =27 degrees C to > or =60 degrees C at different constant pi above pi(e). DPPC showed the abrupt expansion expected for the TC-LE phase transition, followed by the contraction produced by collapse. Supercompressed CLSE showed no evidence of the TC-LE expansion, arguing that supercompression did not simply convert the mixed lipid film to TC DPPC. For both DPPC and CLSE, the melting point, taken as the temperature at which collapse began, increased at higher pi, in contrast to 1-palmitoyl-2-oleoyl phosphatidylcholine, for which higher pi produced collapse at lower temperatures. For pi between 50 and 65 mN/m, DPPC melted at 48-55 degrees C, well above the main transition for bilayers at 41 degrees C. At each pi, CLSE melted at temperatures >10 degrees C lower. The distinct melting points for TC DPPC and supercompressed CLSE provide the basis by which the nature of the alveolar film might be determined from the temperature-dependence of pulmonary mechanics.