Nocturnal lizards from a cool-temperate environment have high metabolic rates at low temperatures

Ectotherms from low-temperature environments have higher metabolic rates at low temperatures than those from warm-temperature environments. We predicted that nocturnal lizards, which are active at much lower environmental temperatures than diurnal lizards, would also have higher metabolic rates at low temperatures, and by association a lower thermal sensitivity (Q ₁₀) than diurnal and crepuscular lizards. We measured the rate of oxygen consumption ( [(V)\dot]\textO ₂ \dot{V}{\text{O}}_{ 2} ) of eight cool-temperate species of lizard (four nocturnal, three diurnal, and one crepuscular) at 13 and 26°C and analyzed log transformations of these data using log mass as a covariate. As expected, [(V)\dot]\textO ₂ \dot{V}{\text{O}}_{ 2} was positively correlated with temperature in all eight species, with [(V)\dot]\textO ₂ \dot{V}{\text{O}}_{ 2} being two to four times higher at 26°C than at 13°C. As predicted, at 13°C (but not 26°C) the [(V)\dot]\textO ₂ \dot{V}{\text{O}}_{ 2} was significantly higher in nocturnal than diurnal lizards. Species-specific differences and mass scaling factors explain the patterns of thermal sensitivity seen among these eight lizard species. Thermal sensitivity is strongly influenced by mass, with smaller species generally having higher thermal sensitivity of their metabolic rate, and this result deserves further exploration among other ectotherms. We conclude that, along with the previously reported lower cost of locomotion found in nocturnal lizards, they also partially offset the thermal handicap of activity at low body temperatures by having an elevated [(V)\dot]\textO ₂ \dot{V}{\text{O}}_{ 2} at lower temperatures.     

Cardiorespiratory responses to hypoxia in the African catfish, <Emphasis Type="Italic">Clarias gariepinus</Emphasis> (Burchell 1822), an air-breathing fish

The African catfish, Clarias gariepinus, possesses a pair of suprabranchial chambers located in the dorsal-posterior part of the branchial cavity having extensions from the upper parts of the second and fourth gill arches, forming the arborescent organs. This structure is an air-breathing organ (ABO) and allows aerial breathing (AB). We evaluated its cardiorespiratory responses to aquatic hypoxia. To determine the mode of air-breathing (obligate or accessory), fish had the respiratory frequency (f _R) monitored and were subjected to normoxic water (PwO₂ = 140 mmHg) without becoming hyperactive for 30 h. During this period, all fish survived without displaying evidences of hyperactivity and maintained unchanged f _R, confirming that this species is a facultative air-breather. Its aquatic O₂ uptake ( [(V)\dot]\textO₂ \dot{V}{\text{O}}_{2} ) was maintained constant down to a critical PO₂ (PcO₂) of 60 mmHg, below which [(V)\dot]\textO₂ \dot{V}{\text{O}}_{2} declined linearly with further reductions of inspired O₂ tension (PiO₂). Just above the PcO₂ the ventilatory tidal volume (V _T) increased significantly along with gill ventilation ( [(V)\dot]_\textG \dot{V}_{\text{G}} ), while f _R changed little. Consequently, the water convection requirement ( [(V)\dot]_\textG /[(V)\dot]\textO₂ ) \left( {\dot{V}_{\text{G}} /\dot{V}{\text{O}}_{2} } \right) increased steeply. This threshold applied to a cardiac response that included reflex bradycardia. AB was initiated at PiO₂ = 140 mmHg (normoxia) and air-breathing episodes increased linearly with more severe hypoxia, being significantly higher at PiO₂ tensions below the PcO₂. Air-breathing episodes were accompanied by bradycardia pre air-breath, to tachycardia post air-breath.     

Environment and feeding change the ability of heart rate to predict metabolism in resting Steller sea lions (<Emphasis Type="Italic">Eumetopias jubatus</Emphasis>)

The ability to use heart rate (fh) to predict oxygen consumption rates ( [(V)\dot]_\textO2 \dot{V}_{{{\text{O}}_{2} }} ) in Steller sea lions and other pinnipeds has been investigated in fasting animals. However, it is unknown whether established fh: [(V)\dot]_\textO2 \dot{V}_{{{\text{O}}_{2} }} relationships hold under more complex physiological situations, such as when animals are feeding or digesting. We assessed whether fh could accurately predict [(V)\dot]_\textO2 \dot{V}_{{{\text{O}}_{2} }} in trained Steller sea lions while fasting and after being fed. Using linear mixed-effects models, we derived unique equations to describe the fh: [(V)\dot]_\textO2 \dot{V}_{{{\text{O}}_{2} }} relationship for fasted sea lions resting on land and in water. Feeding did not significantly change the fh: [(V)\dot]_\textO2 \dot{V}_{{{\text{O}}_{2} }} relationship on land. However, Steller sea lions in water displayed a different fh: [(V)\dot]_\textO2 \dot{V}_{{{\text{O}}_{2} }} relationship after consuming a 4-kg meal compared with the fasting condition. Incorporating comparable published fh: [(V)\dot]_\textO2 \dot{V}_{{{\text{O}}_{2} }} data from Steller sea lions showed a distinct effect of feeding after a 6-kg meal. Ultimately, our study illustrated that both feeding and physical environment are statistically relevant when deriving [(V)\dot]_\textO2 \dot{V}_{{{\text{O}}_{2} }} from telemetered fh, but that only environment affects the practical ability to predict metabolism from fh. Updating current bioenergetic models with data gathered using these predictive fh: [(V)\dot]_\textO2 \dot{V}_{{{\text{O}}_{2} }} equations will yield more accurate estimates of metabolic rates of free-ranging Steller sea lions under a variety of physiological, behavioral, and environmental states.     

Finite element–based injury metrics for pulmonary contusion via concurrent model optimization

This study explores the relationship between impact severity and resulting pulmonary contusion (PC) for four impact conditions using a rat model of the injury. The force–deflection response from a Finite Element (FE) model of the lung was simultaneously matched to experimental data from distinct impacts via a genetic algorithm optimization. Sprague-Dawley rats underwent right-side thoracotomy prior to impact. Insults were applied directly to the lung via an instrumented piston. Five cohorts were tested: a sham group and four groups experiencing lung insults of varying degrees of severity. The values for impact velocity (V) and penetration depth (D) of the cohorts were Group 1, (V = 6.0 m · s⁻¹, D = 5.0 mm), Group 2, (V = 1.5 m · s⁻¹,D = 5.0 mm), Group 3, (V = 6 m · s⁻¹, D = 2.0 mm), and Group 4, (V = 1.5 m · s⁻¹, D = 2.0 mm). CT scans were acquired at 24 h, 48 h, and 1 week post-insult. Contusion volume was determined through segmentation. FE-based injury metrics for PC were determined at 24 h and 1 week post-impact, based on the observed volume of contusion and first principal strain. At 24 h post-impact, the volume of high radiopacity lung (HRL) was greatest for the severe impact group (mean HRL = 9.21 ± 4.89) and was significantly greater than all other cohorts but Group 3. The concurrent optimization matched simulated and observed impact energy within one standard deviation for Group 1 (energy = 3.88 ± 0.883 mJ, observed vs. 4.47 mJ, simulated) and Group 2 (energy = 1.46 ± 0.403 mJ, observed vs. 1.50 mJ, simulated) impacts. Statistically significant relationships between HRL and impact energy are presented. The FEA-based injury metrics at 24 h post-contusion are e_max·[(e)\dot]_max{\varepsilon_{\max}\cdot \dot {\varepsilon}_{\max}} exceeding 94.5 s⁻¹, ε _max exceeding 0.284 and [(e)\dot]_max{\dot{\varepsilon}_{\max}} exceeding 470 s⁻¹. Thresholds for injury to the lung still present at 1 week post-impact were also determined. They are e_max·[(e)\dot]_max{\varepsilon_{\max}\cdot \dot {\varepsilon}_{\max}} exceeding 149 s⁻¹, ε _max exceeding 0.343 and [(e)\dot]_max{\dot{\varepsilon}_{\max}} exceeding 573 s⁻¹. A mesh sensitivity study found that thresholds based on strain rate were more sensitive to changes to mesh density than the threshold based on strain only.     

AMP-activated protein kinase plays a role in initiating metabolic rate suppression in goldfish hepatocytes

In the present study, we test the hypothesis that AMP-activated protein kinase (AMPK) initiates metabolic rate suppression in isolated goldfish hepatocytes. To accomplish this, we attempted to pharmacologically activate AMPK in goldfish hepatocytes with 5-aminoimidazole-4-carboxamide ribonucleoside (AICAR) and the thienopyridone, A769662, to examine the effects of AMPK activation on eukaryotic elongation factor-2 (eEF2), protein synthesis, and cellular oxygen consumption rate ( [(M)\dot]_{\textO 2} \dot{M}_{{{\text{O}}_{ 2} }} ). Goldfish hepatocytes treated with 1 mM AICAR under normoxic conditions (>200 μM O₂) showed a modest but significant 1.1-fold increase in AMPK phosphorylation, a 7.5-fold increase in AMPK activity, a 1.4-fold increase in eEF2 phosphorylation, and a 24% decrease in [(M)\dot]_{\textO 2} \dot{M}_{{{\text{O}}_{ 2} }} . At physiologically relevant [O₂] (<40 μM O₂), the addition of 1 mM AICAR resulted in only a 13% decrease in cellular [(M)\dot]_{\textO 2} \dot{M}_{{{\text{O}}_{ 2} }} with no change in sensitivity to [O₂] as assessed by estimates of cellular P₅₀ and P₉₀ values. The addition of compound C, a general protein kinase inhibitor, after AICAR incubation did not reverse the effects of AICAR on [(M)\dot]_{\textO 2} \dot{M}_{{{\text{O}}_{ 2} }} in normoxia. Treatment of hepatocytes with ≤200 μM A769662 did not affect AMPK activity, AMPK phosphorylation, eEF2 phosphorylation, or cellular [(M)\dot]_{\textO 2} \dot{M}_{{{\text{O}}_{ 2} }} . These data suggest that A769662 is not an activator of AMPK in goldfish hepatocytes. Although our study provides support for the hypothesis that AMPK plays a role in initiating metabolic rate suppression in goldfish hepatocytes, this support must be viewed cautiously because of the known off-target effects of the pharmacological agents used.     

Using light as a lure is an efficient predatory strategy in <Emphasis Type="Italic">Arachnocampa flava,</Emphasis> an Australian glowworm

Trap-building, sit-and-wait predators such as spiders, flies and antlions tend to have low standard metabolic rates (SMRs) but potentially high metabolic costs of trap construction. Members of the genus Arachnocampa (glowworms) use an unusual predatory strategy: larvae bioluminesce to lure positively phototropic insects into their adhesive webs. We investigated the metabolic costs associated with bioluminescence and web maintenance in larval Arachnocampa flava. The mean rate of CO₂ production ([(V)\dot] \dot{V}CO₂) during continuous bioluminescence was 4.38 μl h⁻¹ ± 0.78 (SEM). The mean [(V)\dot] \dot{V}CO₂ of inactive, non-bioluminescing larvae was 3.49 ± 0.35 μl h⁻¹. The mean [(V)\dot] \dot{V}CO₂ during web maintenance when not bioluminescencing was 8.95 ± 1.78 μl h⁻¹, a value significantly lower than that measured during trap construction by other predatory arthropods. These results indicate that bioluminescence itself is not energetically expensive, in accordance with our prediction that a high cost of bioluminescence would render the Arachnocampa sit-and-lure predatory strategy inefficient. In laboratory experiments, both elevated feeding rates and daily web removal caused an increase in bioluminescent output. Thus, larvae increase their investment in light output when food is plentiful or when stressed through having to rebuild their webs. As light production is efficient and the cost of web maintenance is relatively low, the energetic returns associated with continuing to glow may outweigh the costs of continuing to attract prey.     

Average shear rate in three pneumatic bioreactors

A method proposed in recent literature was applied to evaluate the average shear rate ( [(g)\dot]_av ) \left( {\dot{\gamma }_{\rm av} } \right) in three pneumatic bioreactors of 5-dm³ working volume: bubble column, split airlift, and concentric-tube airlift. The volumetric oxygen transfer coefficient (k _L a) is the appropriate characteristic parameter to assess the average shear rate ( [(g)\dot]_av ) \left( {\dot{\gamma }_{\rm av} } \right) in this methodology. Correlations for [(g)\dot]_av \dot{\gamma }_{\rm av} as a function of superficial gas velocity in the riser region (U _GR) and rheological fluid properties (consistency index, K, and flow index, n) were obtained for each model of pneumatic bioreactor studied. The [(g)\dot]_av \dot{\gamma }_{\rm av} values estimated by the proposed methodology lay within the range of values calculated by classical correlations. The proposed correlations were utilized to predict the [(g)\dot]_av \dot{\gamma }_{\rm av} during the Streptomyces clavuligerus cultivations carried out at the same specific air flow rate (3.5 vvm) in the different types of pneumatic bioreactors. The lowest values of [(g)\dot]_av \dot{\gamma }_{\rm av} related to the highest values of consistency index (K) were found for the bubble column bioreactor, and the highest values of [(g)\dot]_av \dot{\gamma }_{\rm av} related to the lowest values of K were found for the concentric-tube airlift bioreactor. Intermediate values were found for the split airlift bioreactor. The results showed that high [(g)\dot]_av \dot{\gamma }_{\rm av} values affect the structural health of the mycelia by the rupture of the hipha.     

Influence of long-term hypoxia on the energy metabolism of the haemoglobin-containing bivalve Scapharca inaequivalvis: critical O2 levels for metabolic depression

Summary The oxygen consumption rate of Scapharca inaequivalvis measured under normoxic conditions over 48 h showed a significant daily cycle with lowest values occurring shortly after the dark period; all hypoxia exposure experiments were carried out during the declining part of the cycle. Animals were exposed to a constant level of hypoxia for a 12-h period in a series of 14 experiments, each at a different oxygen tension. The oxygen consumption was measured continuously, and the extent of accumulation of end-products (succinate and propionate), and the inhibitory effect of adenosine triphosphate on phosphofructokinase were determined at the end of exposures. All three parameters (oxygen consumption, end-product accumulation, phosphofructokinase inhibition) showed a remarkable correlation with major changes occurring between 2.5 and 1.5 ppm (7 and 4 kPa) O₂. The oxygen consumption rates showed a drop to 6% of the normoxic rate, but a consistent low consumption remained below 2 ppm (5.5 kPa) which partly recovered over the 12-h exposure period by about three-fold. Succinate and propionate accumulated progressively between 2.5 and 1.5 ppm (7 and 4 kPa); at [O₂]<1.5 ppm (4kPa) the concentration did not increase further, indicating that anaerobic metabolism had reached a maximum. Over the same range, phosphofructokinase showed an increased sensitivity for adenosine triphosphate, the lower inhibitor concentration at 50% V _max value pointing to depression of glycolytic rate. Despite the activation of anaerobic metabolism and the evident depression of aerobic metabolism, simple calculation demonstrates that Scapharca inaequivalvis relies mainly on aerobic metabolism even during severe hypoxia. It is assumed that the occurrence of haemoglobin in this species is essential for its capacity to survive long periods of hypoxia.Abbreviations ATP adenosine triphosphate - I₅₀ inhibitor concentration at 50% V _max - PFK phosphofructokinase - P _c critical PO₂ - SEM standard error of mean - VO₂ oxygen consumption rate - ww wet weight     

The response of interleukin-6 and soluble interleukin-6 receptor isoforms following intermittent high intensity and continuous moderate intensity cycling

As interleukin-6 (IL-6), its soluble receptor (sIL-6R), and the IL-6/sIL-6R complex is transiently elevated in response to prolonged moderate-intensity exercise, this study investigated how these levels would be modulated by an acute bout of high-intensity intermittent (HIIT) exercise in comparison to continuous moderate-intensity exercise (MOD). This study also investigated the expression of the differentially spliced sIL-6R (DS-sIL-6R) in response to exercise. Eleven healthy males completed two exercise trials matched for external work done (582 ± 82 kJ). During MOD, participants cycled at 61.8 (2.6)% VO_2peak for 58.7 (1.9) min, while HIIT consisted of ten 4-min intervals cycling at 87.5 (3.4)% [(V)\dot]O_2peak \dot{V}{{\hbox{O}}_{2{\rm{peak}}}} separated by 2-min rest. Blood samples were collected pre-exercise, post-exercise, and 1.5, 6, and 23 h post-exercise. Plasma IL-6, sIL-6R, IL-6/sIL-6R complex, and DS-sIL-6R levels were measured by enzyme-linked immunosorbent assay. HIIT caused a significantly greater increase in IL-6 than MOD (P = 0.018). Both MOD and HIIT resulted in an increase in sIL-6R and IL-6/sIL-6R complex (P < 0.001), however, this was not significantly different between trials. Soluble IL-6R peaked at 6 h post-exercise in both trials. DS-sIL-6R increased significantly with exercise (P = 0.02), representing 0.49% of the total sIL-6R increase. This investigation has demonstrated that the IL-6 response is greater after intermittent high-intensity exercise than comparable moderate-intensity exercise; however, increased IL-6/sIL-6R complex nor sIL-6R was different between HIIT and MOD. The current study has shown for the first time that elevated sIL-6R after HIIT exercise is derived from both proteolytic cleavage and differential splicing.     

Oxygen deficits incurred during 45, 60, 75 and 90-s maximal cycling on an air-braked ergometer

The aims of this study were to determine the most appropriate duration for the measurement of the maximal accumulated O₂ deficit (MAOD), which is analogous to the anaerobic capacity, to ascertain the effects of mass, fat free mass (FFM), leg volume (V _leg) and lower body volume (V _1b) on anaerobic test performance, to examine the reproducibility for peak power output ( ) or maximal anaerobic power using an air-braked cycle ergometer and to produce approximations for the percentages of aerobic and anaerobic metabolism during exercise of short duration but high intensity. A group of 12 endurance trained cyclists [mean age 25.1 (SD 4.6) years; mean body mass 73.43 (SD 7.12) kg; mean maximal oxygen consumption 5.12 (SD 0.35) l·min^–1; mean body fat 12.5 (SD 4.1) %] accordingly performed four counterbalanced treatments of 45, 60, 75 and 90 s of maximal cycling on an air-braked ergometer. The mean O₂ deficit of 3.52 l for the 45-s treatment was significantly less (P < 0.01) than those for the 60 (3.75 l), 75 (3.80 l) and 90-s (3.75 l) treatments. These data therefore indicate that in predominantly aerobically trained subjects the O₂ deficit attains a plateau after 60 s of maximal cycling on an air-braked ergometer. Statistically significant interclass correlation coefficients (P<0.05) between the anthropometric variables (mass, FFM, V _leg and V_1b) and or maximal anaerobic power (0.624–0.748) and MAOD (ml) or anaerobic capacity (0.666–0.772) furthermore would suggest the relevance of taking into account muscle mass during anaerobic tests. Intraclass correlation coefficients (0.935–0.946; all P<0.001) would indicate a high degree of reliability for the measurement of . The relative importance of anaerobic work decreased from 60% for the 45-s test to 40% for the 90-s one. Hence our study showed that both aerobic and anaerobic metabolism contributed significantly during all-out tests of 45–90 s duration.     

Habitual physical activity and peak anaerobic power in elderly women

The aim of this study was to investigate the relationship between maximal anaerobic power (P _max) and corresponding optimal velocity (V _opt) and habitual physical activity (PA) on the one hand and with maximal oxygen consumption (V˙O_2max) on the other hand, in elderly women. Twenty-nine community dwelling, healthy women aged 66–82 years participated in the study. PA was evaluated using the Questionnaire d'Activite Physique Saint-Etienne (QAPSE) and expressed using two QAPSE activity indices: mean habitual daily energy expenditure (MHDEE) and daily energy expenditure corresponding to leisure time sports activities (sports activity). The subjects' P _max and V _opt were measured while they cycled on a friction-loaded non-isokinetic cycle ergometer. P _max was expressed relative to body mass [P _max/kg(W · kg⁻¹)], and relative to the mass of two quadriceps muscles [P _{max /Quadr}(W·kg_Quadr ⁻¹)]. A negative relationship between P _max/kg (Spearman's r = −0.56; P < 0.01), P _max/Quadr (r = −0.53; P < 0.01) and V _opt (r = −0.45; P < 0.05) and age was found. P _max/kg was positively associated with MHDEE (r = 0.51; P < 0.01) and sports activity (r = 0.58; P < 0.01), as were P _max/Quadr and V _opt (r = 0.55; P < 0.01 and r = 0.54; P < 0.01, respectively). P _max/kg, P _max/Quadr and V _opt correlated positively with V˙O_2max. The positive relationship between ergometer measurements and PA indices was similar to that between V˙O_2max and PA. P _max/kg was, moreover, closely related to V _opt (r = 0.77; P < 0.001). When a multiple stepwise regression analysis was used to select the variables influencing ergometer measurements, MHDEE contributed significantly to P _max/kg variance, whereas sports activity contributed to P _max/Quadr and V _opt variances. In conclusion, the data from this cross-sectional study suggest that in healthy elderly women habitual PA, and especially leisure time PA, alleviates the decline of the P _max of the quadriceps muscles. Accepted: 30 January 1997     

Effect of anthropometric characteristics and socio-economic status on physical performances of pre-pubertal children living in Bolivia at low altitude

We have previously observed that 11-year-old children of low socio-economic status (LSES) showed a delayed physical growth of approximately 2 years and developed lower normalized short-term power output than children of high socio-economic status (HSES) of the same age. In contrast, maximal oxygen uptake per unit of fat free mass was no different in either group. The aim of this study was to evaluate the effect of anthropometric characteristics between HSES and LSES prepubertal children in aerobic and anaerobic performance. To compare children of the same body dimensions, 11-year-old boys (n = 30) and girls (n = 31) of LSES and 9-year-old boys (n = 21) and girls (n = 27) of HSES were studied. Anthropometric measurements, (direct test), maximal anaerobic power (P _max, force-velocity test) and mean anaerobic power ( , Wingate test) were determined. In these children having the same body dimensions: mean were the same in LSES and HSES children [1.2 (SD 0.2)1-min^–1];P _max and were lower in LSES subjects [154.0 (SD 33.2) vs 174.6 (SD 38.4) W and 116.3 (SD 23.3) vs 128.2 (SD 28.0) W, respectively]; the linear relationships between and fat free mass were the same in LSES and HSES boys but, in the girls, the LSES group had lower values. For anaerobic performance, the relationships were significantly different: the slopes were the same but LSES values for the both sexes were lower. These results would suggest that factors other than differences in body dimensions alone were responsible for the lower performance of LSES girls and boys. Cultural factors and motor learning, structural and functional alterations of muscle induced by marginal malnutrition have been discussed.     

Inhibition of growth by imadazol(on)e propionic acid: Evidence in vivo for coordination of histidine catabolism with the catabolism of other amino acids

Summary Imidazole propionic acid (ipa), a gratuitous inducer of the histidine-utilization (hut) system in Salmonella typhimurium, inhibits the organism's growth on succinate minimal medium. Induction of the hut system is necessary, but not sufficient, to cause inhibition. A study of the ability of single amino acids to relieve ipa-restricted growth suggests that insufficient glutamate is the cause of slow growth. The inhibition of growth by imidazolone propionic acid (iopa), an intermediate in the catabolism of histidine to glutamate, is similar to that by ipa. Studies using 2, 3, 5-triphenyl tetrazolium chloride plates to examine amino acid catabolism suggest that accumulation of ipa or iopa leads to inactivation of aspartate amino-transferase (AAT). This interpretation is supported by studies of an Escherichia coli mutant lacking AAT. The mutant grows poorly on succinate minimal medium, and the poor growth is relieved by the same amino acids that relieve ipa- and iopa-restricted growth. These and other findings are discussed in terms of coordination of the histidine-utilization system with enzymatic activities involved in the catabolism of other amino acids.     

Photosynthetic H<Subscript>2</Subscript> metabolism in <Emphasis Type="Italic">Chlamydomonas reinhardtii</Emphasis> (unicellular green algae)

Unicellular green algae have the ability to operate in two distinctly different environments (aerobic and anaerobic), and to photosynthetically generate molecular hydrogen (H₂). A recently developed metabolic protocol in the green alga Chlamydomonas reinhardtii permitted separation of photosynthetic O₂-evolution and carbon accumulation from anaerobic consumption of cellular metabolites and concomitant photosynthetic H₂-evolution. The H₂ evolution process was induced upon sulfate nutrient deprivation of the cells, which reversibly inhibits photosystem-II and O₂-evolution in their chloroplast. In the absence of O₂, and in order to generate ATP, green algae resorted to anaerobic photosynthetic metabolism, evolved H₂ in the light and consumed endogenous substrate. This study summarizes recent advances on green algal hydrogen metabolism and discusses avenues of research for the further development of this method. Included is the mechanism of a substantial tenfold starch accumulation in the cells, observed promptly upon S-deprivation, and the regulated starch and protein catabolism during the subsequent H₂-evolution. Also discussed is the function of a chloroplast envelope-localized sulfate permease, and the photosynthesis–respiration relationship in green algae as potential tools by which to stabilize and enhance H₂ metabolism. In addition to potential practical applications of H₂, approaches discussed in this work are beginning to address the biochemistry of anaerobic H₂ photoproduction, its genes, proteins, regulation, and communication with other metabolic pathways in microalgae. Photosynthetic H₂ production by green algae may hold the promise of generating a renewable fuel from nature’s most plentiful resources, sunlight and water. The process potentially concerns global warming and the question of energy supply and demand.     

Recovery after anaerobic metabolism in the leech (Hirudo medicinalis L.)

Medicinal leeches (Hirudo medicinalis L.) responded to self-induced hypoxia (72 h) with typical anaerobic metabolism characterized by a decrease in adenylate energy charge, utilization of the substrates glycogen and malate, and accumulation of the main anaerobic endproducts succinate and propionate. Propionate was also excreted into the medium. Ammonia excretion was suppressed. Aerobic recovery resulted in a profound O₂ debt. Resynthesis of ATP was completed within 30 min. Disposal of succinate and restoring of malate required 2–3 h, and clearance of propionate and recharging of glycogen 6–12 h. Ammonia excretion did not exceed normoxic rates and excretion of propionate during recovery accounted for only 10% of total propionate accumulated during hypoxia. It is postulated that the clearance of succinate and propionate involves oxidation but also resynthesis of malate and glycogen. During hypoxia and recovery blood osmolality remained constant. The Na⁺ and Cl^- ion concentrations in blood, the decrease of which was nearly equimolar during hypoxia, were re-established following different time-courses. Na⁺ concentration returned to normoxic levels after 2–3 h. The delayed increase in Cl^- concentration, however, correlating with 6–12 h necessary to clear blood propionate, is interpretated as an anion regulating effect.Abbreviations AEC adenylate energy charge; fw, fresh weight - HPLC high-performance liquid chromatography - SCCA shortchain carboxylic acids     

Changes in skeletal muscle oxygenation during incremental exercise measured with near infrared spectroscopy

To determine the change in muscle oxygenation in response to progressively increasing work rate exercise, muscle oxyhemoglobin + oxymyoglobin saturation was measured transcutaneously with near infrared spectroscopy in the vastus lateralis muscle during cycle ergometry. Studies were done in 11 subjects while gas exchange was measured breath-by-breath. As work rate was increased, tissue oxygenation initially either remained constant near resting levels or, more usually, decreased. Near the work rate and metabolic rate where significant lactic acidosis was detected by excess CO₂ production (lactic acidosis threshold, LAT), muscle oxygenation decreased more steeply. As maximum oxygen uptake ( ) was approached, the rate of desaturation slowed. In 8 of the 11 subjects, tissue O₂ saturation reached a minimum which was sustained for 1–3 min before was reached. The LAT correlated with both the (r = 0.95,P < 0.0001) and the work rate (r = 0.94,P < 0.0001) at which the rate of tissue O₂ desaturation accelerated. These results describe a consistent pattern in the rate of decrease in muscle oxygenation, slowly decreasing over the lower work rate range, decreasing more rapidly in the work rate range of the LAT and then slowing at about 80% of , approaching or reaching a minimum saturation at .