The scaling of ground reaction forces and duty factor in monitor lizards: implications for locomotion in sprawling tetrapods

Geometric scaling predicts a major challenge for legged, terrestrial locomotion. Locomotor support requirements scale identically with body mass (α M¹), while force-generation capacity should scale α M^2/3 as it depends on muscle cross-sectional area. Mammals compensate with more upright limb postures at larger sizes, but it remains unknown how sprawling tetrapods deal with this challenge. Varanid lizards are an ideal group to address this question because they cover an enormous body size range while maintaining a similar bent-limb posture and body proportions. This study reports the scaling of ground reaction forces and duty factor for varanid lizards ranging from 7 g to 37 kg. Impulses (force×time) (α M^0.99−1.34) and peak forces (α M^0.73−1.00) scaled higher than expected. Duty factor scaled α M^0.04 and was higher for the hindlimb than the forelimb. The proportion of vertical impulse to total impulse increased with body size, and impulses decreased while peak forces increased with speed.     

Shape shifting predicts ontogenetic changes in metabolic scaling in diverse aquatic invertebrates

Metabolism fuels all biological activities, and thus understanding its variation is fundamentally important. Much of this variation is related to body size, which is commonly believed to follow a 3/4-power scaling law. However, during ontogeny, many kinds of animals and plants show marked shifts in metabolic scaling that deviate from 3/4-power scaling predicted by general models. Here, we show that in diverse aquatic invertebrates, ontogenetic shifts in the scaling of routine metabolic rate from near isometry (b_R = scaling exponent approx. 1) to negative allometry (b_R < 1), or the reverse, are associated with significant changes in body shape (indexed by b_L = the scaling exponent of the relationship between body mass and body length). The observed inverse correlations between b_R and b_L are predicted by metabolic scaling theory that emphasizes resource/waste fluxes across external body surfaces, but contradict theory that emphasizes resource transport through internal networks. Geometric estimates of the scaling of surface area (SA) with body mass (b_A) further show that ontogenetic shifts in b_R and b_A are positively correlated. These results support new metabolic scaling theory based on SA influences that may be applied to ontogenetic shifts in b_R shown by many kinds of animals and plants.     

Intraspecific Scaling of the Resting and Maximum Metabolic Rates of the Crucian Carp (Carassius auratus)

The question of how the scaling of metabolic rate with body mass (M) is achieved in animals is unresolved. Here, we tested the cell metabolism hypothesis and the organ size hypothesis by assessing the mass scaling of the resting metabolic rate (RMR), maximum metabolic rate (MMR), erythrocyte size, and the masses of metabolically active organs in the crucian carp (Carassius auratus). The M of the crucian carp ranged from 4.5 to 323.9 g, representing an approximately 72-fold difference. The RMR and MMR increased with M according to the allometric equations RMR = 0.212M ^0.776 and MMR = 0.753M ^0.785. The scaling exponents for RMR (b _r) and MMR (b _m) obtained in crucian carp were close to each other. Thus, the factorial aerobic scope remained almost constant with increasing M. Although erythrocyte size was negatively correlated with both mass-specific RMR and absolute RMR adjusted to M, it and all other hematological parameters showed no significant relationship with M. These data demonstrate that the cell metabolism hypothesis does not describe metabolic scaling in the crucian carp, suggesting that erythrocyte size may not represent the general size of other cell types in this fish and the metabolic activity of cells may decrease as fish grows. The mass scaling exponents of active organs was lower than 1 while that of inactive organs was greater than 1, which suggests that the mass scaling of the RMR can be partly due to variance in the proportion of active/inactive organs in crucian carp. Furthermore, our results provide additional evidence supporting the correlation between locomotor capacity and metabolic scaling.     

Metabolic scaling of antibiotics in reptiles: Basis and limitations

The allometric equation y = a · x^b has been used to scale many morphological and physiological attributes relative to body mass. For instance, in eutherian mammals, the equation P_met = 70M_b^0.75 has been used to describe the relationship between metabolic rate (P_met) and body mass (M_b). Similar equations have been derived for squamate reptiles. Recently, this relationship between metabolic rate and body mass has been used in determining appropriate dosages and dosing intervals of antibiotics both intraspecifically for different sized reptiles and interspecifically for those reptiles in which antibiotic pharmacokinetic studies have not been performed. Although this is a simple mathematical process, a number of problems surface when this approach is examined closely. First, the mass constant (a) in reptiles varies from 1–5 for snakes and 6–10 for lizards. No such information is available for chelonians or crocodilians. Unless the mass constant for the unknown species approximates that of the known species, inappropriate dosages and intervals of administration will be calculated. Second, pharmacokinetic differences may exist between widely divergent species, independent of metabolic rate. Third, all available pharmacokinetic studies and metabolic allometric equations are derived from clinically healthy reptiles. Differences more than likely exist between healthy and ill reptiles in regard to uptake, distribution, and elimination of drugs and overall metabolism. While metabolic scaling of antibiotics is a potentially useful and practical tool in drug dosing, these limitations must be considered when dosing an ill reptile. Until more scientifically derived information is available for demonstrating the accuracy of metabolic scaling of antibiotics in reptiles, the clinician will need to understand the limitations of this approach. © 1996 Wiley-Liss, Inc.     

Application of leaf size and leafing intensity scaling across subtropical trees

Understanding the scaling between leaf size and leafing intensity (leaf number per stem size) is crucial for comprehending theories about the leaf costs and benefits in the leaf size–twig size spectrum. However, the scaling scope of leaf size versus leafing intensity changes along the twig leaf size variation in different leaf habit species remains elusive. Here, we hypothesize that the numerical value of scaling exponent for leaf mass versus leafing intensity in twig is governed by the minimum leaf mass versus maximum leaf mass (M _min versus M _max) and constrained to be ≤−1.0. We tested this hypothesis by analyzing the twigs of 123 species datasets compiled in the subtropical mountain forest. The standardized major axis regression (SMA) analyses showed the M _min scaled as the 1.19 power of M _max and the ‐α (−1.19) were not statistically different from the exponents of M _min versus leafing intensity in whole data. Across leaf habit groups, the M _max scaled negatively and isometrically with respect to leafing intensity. The pooled data''s scaling exponents ranged from −1.14 to −0.96 for M _min and M _max versus the leafing intensity based on stem volume (LIV). In the case of M _min and M _max versus the leafing intensity based on stem mass (LIM), the scaling exponents ranged from −1.24 to −1.04. Our hypothesis successfully predicts that the scaling relationship between leaf mass and leafing intensity is constrained to be ≤−1.0. More importantly, the lower limit to scaling of leaf mass and leafing intensity may be closely correlated with M _min versus M _max. Besides, constrained by the maximum leaf mass expansion, the broad scope range between leaf size and number may be insensitive to leaf habit groups in subtropical mountain forest.     

Oligomeric Size of the M2 Muscarinic Receptor in Live Cells as Determined by Quantitative Fluorescence Resonance Energy Transfer

Fluorescence resonance energy transfer (FRET), measured by fluorescence intensity-based microscopy and fluorescence lifetime imaging, has been used to estimate the size of oligomers formed by the M₂ muscarinic cholinergic receptor. The approach is based on the relationship between the apparent FRET efficiency within an oligomer of specified size (n) and the pairwise FRET efficiency between a single donor and a single acceptor (E). The M₂ receptor was fused at the N terminus to enhanced green or yellow fluorescent protein and expressed in Chinese hamster ovary cells. Emission spectra were analyzed by spectral deconvolution, and apparent efficiencies were estimated by donor-dequenching and acceptor-sensitized emission at different ratios of enhanced yellow fluorescent protein-M₂ receptor to enhanced green fluorescent protein-M₂ receptor. The data were interpreted in terms of a model that considers all combinations of donor and acceptor within a specified oligomer to obtain fitted values of E as follows: n = 2, 0.495 ± 0.019; n = 4, 0.202 ± 0.010; n = 6, 0.128 ± 0.006; n = 8, 0.093 ± 0.005. The pairwise FRET efficiency determined independently by fluorescence lifetime imaging was 0.20–0.24, identifying the M₂ receptor as a tetramer. The strategy described here yields an explicit estimate of oligomeric size on the basis of fluorescence properties alone. Its broader application could resolve the general question of whether G protein-coupled receptors exist as dimers or larger oligomers. The size of an oligomer has functional implications, and such information can be expected to contribute to an understanding of the signaling process.     

Scaling relationship between tree respiration rates and biomass

The WBE theory proposed by West, Brown and Enquist predicts that larger plant respiration rate, R, scales to the three-quarters power of body size, M. However, studies on the R versus M relationship for larger plants (i.e. trees larger than saplings) have not been reported. Published respiration rates of field-grown trees (saplings and larger trees) were examined to test this relationship. Our results showed that for larger trees, aboveground respiration rates R_A scaled as the 0.82-power of aboveground biomass M_A, and that total respiration rates R_T scaled as the 0.85-power of total biomass M_T, both of which significantly deviated from the three-quarters scaling law predicted by the WBE theory, and which agreed with 0.81–0.84-power scaling of biomass to respiration across the full range of measured tree sizes for an independent dataset reported by Reich et al. (Reich et al. 2006 Nature 439, 457–461). By contrast, R scaled nearly isometrically with M in saplings. We contend that the scaling exponent of plant metabolism is close to unity for saplings and decreases (but is significantly larger than three-quarters) as trees grow, implying that there is no universal metabolic scaling in plants.     

Size matters: plasticity in metabolic scaling shows body-size may modulate responses to climate change

Variability in metabolic scaling in animals, the relationship between metabolic rate (R) and body mass (M), has been a source of debate and controversy for decades. R is proportional to M^b, the precise value of b much debated, but historically considered equal in all organisms. Recent metabolic theory, however, predicts b to vary among species with ecology and metabolic level, and may also vary within species under different abiotic conditions. Under climate change, most species will experience increased temperatures, and marine organisms will experience the additional stressor of decreased seawater pH (‘ocean acidification’). Responses to these environmental changes are modulated by myriad species-specific factors. Body-size is a fundamental biological parameter, but its modulating role is relatively unexplored. Here, we show that changes to metabolic scaling reveal asymmetric responses to stressors across body-size ranges; b is systematically decreased under increasing temperature in three grazing molluscs, indicating smaller individuals were more responsive to warming. Larger individuals were, however, more responsive to reduced seawater pH in low temperatures. These alterations to the allometry of metabolism highlight abiotic control of metabolic scaling, and indicate that responses to climate warming and ocean acidification may be modulated by body-size.     

Ontogenetic phase shifts in metabolism: links to development and anti-predator adaptation

The allometric relationships between resting metabolism (VO₂) and body mass (M), VO₂ = a_iM^b, are considered a fundamental law of nature. A distinction though needs to be made between the ontogeny (within a species) and phylogeny (among species) of metabolism. However, the nature and significance of the intraspecific allometry (ontogeny of metabolism) have not been established in fishes. In this study, we present experimental evidence that a puffer fish ranging 0.0008–3 g in wet body mass has four distinct allometric phases in which three stepwise increases in scaling constants (a_i, i = 1–4), i.e. ontogenetic phase shifts in metabolism, occur with growth during its early life stages at around 0.002, 0.01 and 0.1 g, keeping each scaling exponent constant in each phase (b = 0.795). Three stepwise increases in a_i accompanied behavioural and morphological changes and three peaks of severe cannibalism, in which the majority of predation occurred on smaller fish that had a lower value of a_i. Though fishes are generally highly fecund, producing a large number of small eggs, their survivability is very low. These results suggest that individuals with the ability to rapidly grow and step up ‘a_i’ develop more anti-predator adaptation as a result of the decreased predatory risk.     

Isometric scaling of above- and below-ground biomass at the individual and community levels in the understorey of a sub-tropical forest

Background and Aims Empirical studies and allometric partitioning (AP) theory indicate that plant above-ground biomass (M_A) scales, on average, one-to-one (isometrically) with below-ground biomass (M_R) at the level of individual trees and at the level of entire forest communities. However, the ability of the AP theory to predict the biomass allocation patterns of understorey plants has not been established because most previous empirical tests have focused on canopy tree species or very large shrubs.Methods In order to test the AP theory further, 1586 understorey sub-tropical forest plants from 30 sites in south-east China were harvested and examined. The numerical values of the scaling exponents and normalization constants (i.e. slopes and y-intercepts, respectively) of log–log linear M_A vs. M_R relationships were determined for all individual plants, for each site, across the entire data set, and for data sorted into a total of 19 sub-sets of forest types and successional stages. Similar comparisons of M_A/M_R were also made.Key Results The data revealed that the mean M_A/M_R of understorey plants was 2·44 and 1·57 across all 1586 plants and for all communities, respectively, and M_A scaled nearly isometrically with respect to M_R, with scaling exponents of 1·01 for all individual plants and 0·99 for all communities. The scaling exponents did not differ significantly among different forest types or successional stages, but the normalization constants did, and were positively correlated with M_A/M_R and negatively correlated with scaling exponents across all 1586 plants.Conclusions The results support the AP theory’s prediction that M_A scales nearly one-to-one with M_R (i.e. M_A ∝ M_R ^≈1·0) and that plant biomass partitioning for individual plants and at the community level share a strikingly similar pattern, at least for the understorey plants examined in this study. Furthermore, variation in environmental conditions appears to affect the numerical values of normalization constants, but not the scaling exponents of the M_A vs. M_R relationship. This feature of the results suggests that plant size is the primary driver of the M_A vs. M_R biomass allocation pattern for understorey plants in sub-tropical forests.     

Leaf Longevity as a Normalization Constant in Allometric Predictions of Plant Production

In metabolic scaling theory the size-dependence of plant processes is described by a power function of form Y=Y _o M ^θ where Y is a characteristic such as plant productivity that changes with plant size (M) raised to the θ ^th power and Y _o is a normalization constant that adjusts the general relationship across environments and species. In essence, the theory considers that the value of θ arises in the size-dependent relationship between leaf area and vascular architecture that influences plant function and that Y _o modulates this general relationship to account for ecological and evolutionary effects on the exchange of resources between plant and environment. Enquist and colleagues have shown from first principles that Y _o is a function of carbon use efficiency, the carbon fraction of a plant, the area-specific carbon assimilation rate of a leaf, the laminar area of a leaf, and the mass of a leaf. We show that leaf longevity provides a functional integration of these traits that can serve as a simpler normalization in scaling plant productivity for individual species and potentially for mixed-species communities as well.     

Ontogenetic body-mass scaling of resting metabolic rate covaries with species-specific metabolic level and body size in spiders and snakes

According to common belief, metabolic rate usually scales with body mass to the 3/4-power, which is considered by some to be a universal law of nature. However, substantial variation in the metabolic scaling exponent (b) exists, much of which can be related to the overall metabolic level (L) of various taxonomic groups of organisms, as predicted by the recently proposed metabolic-level boundaries (MLB) hypothesis. Here the MLB hypothesis was tested using data for intraspecific (ontogenetic) body-mass scaling of resting metabolic rate in spiders and boid snakes. As predicted, in both animal groups b varies mostly between 2/3 and 1, and is significantly negatively related to L. L is, in turn, negatively related to species-specific body mass (M_m: estimated as the mass at the midpoint of a scaling relationship), and as a result, larger species tend to have steeper metabolic scaling slopes (b) than smaller species. After adjusting for the effects of M_m, b and L are still negatively related, though significantly only in the spiders, which exhibit a much wider range of L than the snakes. Therefore, in spiders and snakes the intraspecific scaling of metabolic rate with body mass itself scales with interspecific variation in both metabolic level and body mass.     

Heart mass and the maximum cardiac output of birds and mammals: implications for estimating the maximum aerobic power input of flying animals

Empirical studies of cardiovascular variables suggest that relative heart muscle mass (relative M_h) is a good indicator of the degree of adaptive specialization for prolonged locomotor activities, for both birds and mammals. Reasonable predictions for the maximum oxygen consumption of birds during flight can be obtained by assuming that avian heart muscle has the same maximum physiological and biomechanical performance as that of terrestrial mammals. Thus, data on M_h can be used to provide quantitative estimates for the maximum aerobic power input (aerobic P_i,max) available to animals during intense levels of locomotor activity. The maximum cardiac output of birds and mammals is calculated to scale with respect to M_h (g) as 213 M_h^0.88+-0.04 (ml min^-1), while aerobic P_i,max is estimated to scale approximately as 11 M_h^0.88+-0.09 (W). In general, estimated inter-species aerobic P_i,max, based on M_h for all bird species (excluding hummingbirds), is calculated to scale with respect to body mass (M_b in kg) as 81 M_b^0.82+-0.11 (W). Comparison of family means for M_h indicate that there is considerable diversity in aerobic capacity among birds and mammals, for example, among the medium to large species of birds the Tinamidae have the smallest relative M_h (0.25 per cent) while the Otidae have unusually large relative M_h (1.6 per cent). Hummingbirds have extremely large relative M_h (2.28 per cent), but exhibit significant sexual dimorphism in their scaling of M_h and flight muscle mass, so that when considering hummingbird flight performance it may be useful to control for sexual differences in morphology. The estimated scaling of aerobic P_i,max (based on M_h and M_b in g) for male and female hummingbirds is 0.51 M_b^{0.83 +/-0.07} and 0.44 M_b^{0.85+- 0.11} (W), respectively. Locomotory muscles are dynamic structures and it might be anticipated that where additional energetic ''costs'' occur seasonally (e.g. due to migratory fattening or the development of large secondary sexual characteristics) then the relevant cardiac and locomotor musculature might also be regulated seasonally. This is an important consideration, both due to the intrinsic interest of studying muscular adaptation to changes in energy demand, but also as a confounding variable in the practical use of heart rate to estimate the energetics of animals. Haemoglobin concentration (or haematocrit) may also be a confounding variable. Thus, it is concluded that data on the cardiovascular and flight muscle morphology of animals provides essential information regarding the behavioural, ecological and physiological significance of the flight performance of animals.     

Heterologous production and characterisation of two distinct dihaem-containing membrane integral cytochrome b561 enzymes from Arabidopsis thaliana in Pichia pastoris and Escherichia coli cells

Cytochrome (cyt) b₅₆₁ proteins are dihaem-containing membrane proteins, belonging to the CYBASC (cytochrome-b₅₆₁-ascorbate-reducible) family, and are proposed to be involved in ascorbate recycling and/or the facilitation of iron absorption. Here, we present the heterologous production of two cyt b₅₆₁ paralogs from Arabidopsis thaliana (Acytb₅₆₁-A, Acytb₅₆₁-B) in Escherichia coli and Pichia pastoris, their purification, and initial characterisation. Spectra indicated that Acytb₅₆₁-A resembles the best characterised member of the CYBASC family, the cytochrome b₅₆₁ from adrenomedullary chromaffin vesicles, and that Acytb₅₆₁-B is atypical compared to other CYBASC proteins. Haem oxidation–reduction midpoint potential (E_M) values were found to be fully consistent with ascorbate oxidation activities and Fe^3 +-chelates reductase activities. The ascorbate dependent reduction and protein stability of both paralogs were found to be sensitive to alkaline pH values as reported for the cytochrome b₅₆₁ from chromaffin vesicles. For both paralogs, ascorbate-dependent reduction was inhibited and the low-potential haem E_M values were affected significantly by incubation with diethyl pyrocarbonate (DEPC) in the absence of ascorbate. Modification with DEPC in the presence of ascorbate left the haem E_M values unaltered compared to the unmodified proteins. However, ascorbate reduction was inhibited. We concluded that the ascorbate-binding site is located near the low-potential haem with the Fe^3 +-chelates reduction-site close to the high-potential haem. Furthermore, inhibition of ascorbate oxidation by DEPC treatment occurs not only by lowering the haem E_M values but also by an additional modification affecting ascorbate binding and/or electron transfer. Analytical gel filtration experiments suggest that both cyt b₅₆₁ paralogs exist as homodimers.     

Maximum ingested food size in captive strepsirrhine primates: Scaling and the effects of diet

Little is known about ingested food size (V_b) in primates, even though this variable has potentially important effects on food intake and processing. This study provides the first data on V_b in strepsirrhine primates using a captive sample of 17 species. These data can be used for generating and testing models of feeding energetics. Strepsirrhines are of interest because they are hypometabolic and chewing rate and daily feeding time do not show a significant scaling relationship with body size. Using melon, carrot, and sweet potato we found that maximum V_b scales isometrically with body mass and mandible length. Low dietary quality in larger strepsirrhines might explain why V_b increases with body size at a greater rate than does resting metabolic rate. Relative to body size, V_b is large in frugivores but small in folivores; furthermore scaling slopes are higher in frugivores than in folivores. A gross estimate of dietary quality explains much of the variation in V_b that is not explained by body size. Gape adaptations might favor habitually large bites for frugivores and small ones for folivores. More data are required for several feeding variables and for wild populations. Am J Phys Anthropol 142:625–635, 2010. © 2010 Wiley‐Liss, Inc.     

Environmental modulation of metabolic allometry in ornate rainbowfish Rhadinocentrus ornatus

The nature of the relationship between the metabolic rate (MR) and body mass (M) of animals has been the source of controversy for over seven decades, with much of the focus on the value of the scaling exponent b, where MR is proportional to M^b. While it is well known that MR does not generally scale isometrically (i.e. b is seldom equal to 1), the value of b remains the subject of heated debate. In the present study, we examine the influence of an ecologically relevant abiotic variable, pH, on the metabolic allometry of an Australian freshwater fish, Rhadinocentrus ornatus. We show that the value of b is lower for rainbowfish acclimated to acidic (pH 5.0) conditions compared to rainbowfish acclimated to alkaline conditions (pH 8.5), but that acute exposure to altered pH does not alter the value of b. This significant effect of an abiotic variable on metabolic allometry supports a growing body of evidence that there is no universal value of b and demonstrates that experimental manipulations of metabolic allometry represent powerful, and as yet underused, tools to understand the factors that constrain and influence the allometry of metabolic rate.     

The Effects of Temperature and Body Mass on Jump Performance of the Locust Locusta migratoria

Locusts jump by rapidly releasing energy from cuticular springs built into the hind femur that deform when the femur muscle contracts. This study is the first to examine the effect of temperature on jump energy at each life stage of any orthopteran. Ballistics and high-speed cinematography were used to quantify the energy, distance, and take-off angle of the jump at 15, 25, and 35°C in the locust Locusta migratoria. Allometric analysis across the five juvenile stages at 35°C reveals that jump distance (D; m) scales with body mass (M; g) according to the power equation D = 0.35M ^{0.17±0.08 (95% CI)}, jump take-off angle (A; degrees) scales as A = 52.5M ^0.00±0.06, and jump energy (E; mJ per jump) scales as E = 1.91M ^1.14±0.09. Temperature has no significant effect on the exponent of these relationships, and only a modest effect on the elevation, with an overall Q₁₀ of 1.08 for jump distance and 1.09 for jump energy. On average, adults jump 87% farther and with 74% more energy than predicted based on juvenile scaling data. The positive allometric scaling of jump distance and jump energy across the juvenile life stages is likely facilitated by the concomitant relative increase in the total length (L _f+t; mm) of the femur and tibia of the hind leg, L _f+t = 34.9M ^0.37±0.02. The weak temperature-dependence of jump performance can be traced to the maximum tension of the hind femur muscle and the energy storage capacity of the femur''s cuticular springs. The disproportionately greater jump energy and jump distance of adults is associated with relatively longer (12%) legs and a relatively larger (11%) femur muscle cross-sectional area, which could allow more strain loading into the femur''s cuticular springs. Augmented jump performance in volant adult locusts achieves the take-off velocity required to initiate flight.     

High-Throughput Tissue Bioenergetics Analysis Reveals Identical Metabolic Allometric Scaling for Teleost Hearts and Whole Organisms

Organismal metabolic rate, a fundamental metric in biology, demonstrates an allometric scaling relationship with body size. Fractal-like vascular distribution networks of biological systems are proposed to underlie metabolic rate allometric scaling laws from individual organisms to cells, mitochondria, and enzymes. Tissue-specific metabolic scaling is notably absent from this paradigm. In the current study, metabolic scaling relationships of hearts and brains with body size were examined by improving on a high-throughput whole-organ oxygen consumption rate (OCR) analysis method in five biomedically and environmentally relevant teleost model species. Tissue-specific metabolic scaling was compared with organismal routine metabolism (RMO₂), which was measured using whole organismal respirometry. Basal heart OCR and organismal RMO₂ scaled identically with body mass in a species-specific fashion across all five species tested. However, organismal maximum metabolic rates (MMO₂) and pharmacologically-induced maximum cardiac metabolic rates in zebrafish Danio rerio did not show a similar relationship with body mass. Brain metabolic rates did not scale with body size. The identical allometric scaling of heart and organismal metabolic rates with body size suggests that hearts, the power generator of an organism’s vascular distribution network, might be crucial in determining teleost metabolic rate scaling under routine conditions. Furthermore, these findings indicate the possibility of measuring heart OCR utilizing the high-throughput approach presented here as a proxy for organismal metabolic rate—a useful metric in characterizing organismal fitness. In addition to heart and brain OCR, the current approach was also used to measure whole liver OCR, partition cardiac mitochondrial bioenergetic parameters using pharmacological agents, and estimate heart and brain glycolytic rates. This high-throughput whole-organ bioenergetic analysis method has important applications in toxicology, evolutionary physiology, and biomedical sciences, particularly in the context of investigating pathogenesis of mitochondrial diseases.     

Synergistic property of cordycepin in cultivated Cordyceps militaris-mediated apoptosis in human leukemia cells

Cordyceps militaris is a well-known Chinese traditional medicinal mushroom frequently used for tonics and recently of a potential interest for cancer intervention. Here, we explored the cancer cell killing activity of the hot water extracts of C. militaris cultured mycelia (CM_MY) and cultivated fruiting bodies (CM_FB). We found that CM_FB exhibited a greater cytotoxic effect against various cancer cells over CM_MY. Apoptotic phenotypes including apoptotic body formation, DNA laddering, caspase 3 activation and cleavage of PARP proteins were induced by CM_FB treatment but only slightly induced by same concentration of CM_MY treatment in human HL-60 leukemia cells. Cordycepin in CM_FB (10.47 mg/g) is significantly higher (∼15.2 times) than that of CM_MY (0.69 mg/g). Using isobolographic analysis, the synergy of cytotoxicity was observed across different combined concentrations of CM_MY and cordycepin. By complementing cordycepin into CM_MY to the level comparable with CM_FB, we observed that CM_MY (500 μg/ml) with cordycepin (4.8 μg/ml) induced apoptosis to a level similar to that induced by CM_FB (500 μg/ml). Together, our results suggest that cordycepin possesses a synergistic cytotoxic effect with Cordyceps militaris-mediated apoptosis in human leukemia cells and therefore explaining a better anti-proliferating activity of CM_FB over CM_MY.