Role of kallikrein-kininogen system in insulin-stimulated glucose transport after muscle contractions.

Serum proteins [molecular weight (MW) > 10,000] are essential for increased insulin-stimulated glucose transport after in vitro muscle contractions. We investigated the role of the kallikrein-kininogen system, including bradykinin, which is derived from kallikrein (MW > 10,000)-catalyzed degradation of serum protein kininogen (MW > 10,000), on this contraction effect. In vitro electrical stimulation of rat epitrochlearis muscles was performed in 1) rat serum +/- kallikrein inhibitors; 2) human plasma (normal or kallikrein-deficient); 3) rat serum +/- bradykinin receptor-2 inhibitors; or 4) serum-free buffer +/- bradykinin. 3-O-methylglucose transport (3-MGT) was measured 3.5 h later. Serum +/- kallikrein inhibitors tended (P = 0.08) to diminish postcontraction insulin-stimulated 3-MGT. Contractions in normal plasma enhanced insulin-stimulated 3-MGT vs. controls, but contractions in kallikrein-deficient plasma did not. Supplementing rat serum with bradykinin receptor antagonist HOE-140 during contraction did not alter insulin-stimulated 3-MGT. Muscles stimulated to contract in serum-free buffer plus bradykinin did not have enhanced insulin-stimulated 3-MGT. Bradykinin was insufficient for postcontraction-enhanced insulin sensitivity. However, results with kallikrein inhibitors and kallikrein-deficient plasma suggest kallikrein plays a role in this improved insulin action.     

Effect of duration and exogenous carbohydrate on gross efficiency during cycling

The purpose of this investigation was to determine the effects of 2.5 hours of cycling with and without carbohydrate supplementation on gross efficiency (GE). Trained cyclists (N = 15) were tested for V(.-)O2max (53.6 + 2.2 ml x kg(-1) x min(-1)) and lactate threshold during incremental tests to exhaustion. On 2 separate visits, cyclists performed 2.5 hours of cycling on an indoor trainer. A carbohydrate (C) or placebo (P) beverage was randomly provided and counterbalanced for each of the trials. Gross efficiency, cycling economy, power output, V(.-)O2, lactate, and blood glucose were measured every 20 minutes during the 2.5-hour ride. Muscle glycogen was measured immediately before and after the ride from the vastus lateralis. Results indicated that power output and V(.-)O2 decreased over time (p < 0.05) but were not different between trials. Relative GE and cycling economy during C were greater than P at 40 and 150 minutes (p < 0.05). Blood glucose significantly decreased in P and was lower than C at all time points (p < 0.05). Respiratory exchange ratio decreased over time in both trials, with a significant treatment effect at 40 and 150 minutes (p < 0.05). Muscle glycogen decreased by 65% during both conditions (p < 0.05) but demonstrated no treatment effect. We conclude that carbohydrate supplementation during 2.5 hours of cycling attenuated the decrease in GE possibly by maintaining blood glucose levels. This suggests that the positive effect of carbohydrate supplementation on endurance performance may be through the maintenance of metabolic efficiency.     

Detection of phages carrying the Shiga toxin 1 and 2 genes in waste water and river water samples

AIMS: To evaluate the occurrence and abundance of phages that carry the stx(1) and stx(2) gene in water samples of different quality. METHODS AND RESULTS: Phages growing on the Shiga toxin-negative Escherichia coli O157:H7 (ATCC 43,888) strain were enumerated by a plaque assay in concentrated raw and treated waste water samples and river water samples. Plaques were investigated for the presence of stx(1) and stx(2) genes by a multiplex/nested PCR procedure. An overall number of 805 plaques were tested for the presence of stx-carrying phages. Stx genes could be demonstrated in 2% (stx(1)) and 16% (stx(2)) of the plaques. Stx-phages were eliminated with approximately the same efficiency in comparison with somatic coliphages during the waste water treatment process. CONCLUSIONS: Due to the low numbers of phages carrying the stx genes 1 and 2 in treated waste water and river water, the dilution and inactivation of host bacteria and the unsuitable conditions for the transduction of host organisms in aquatic environments, it is difficult to derive from the data the direct evidence for a public health problem. SIGNIFICANCE AND IMPACT OF THE STUDY: The results show the quantitative occurrence of stx-carrying phages in waste and river water and confirm the frequent circulation of these viruses in the aquatic environment.     

Heart rate at lactate threshold and cycling time trials

The purpose of this investigation was to relate the heart rate and lactate response during simulated cycling time trials to incremental laboratory tests. Subjects (N = 10) were tested for .V(O2)max (56.1 +/- 2.4 ml.kg(-1).min(-1) ) and lactate threshold during incremental tests to exhaustion. Power output and heart rate (HR) at threshold was assessed by 3 methods: lactate deflection point (LaT), onset of blood lactate accumulation (OBLA), and the point on the lactate curve at maximal distance from a line connecting starting and finishing power output (Dmax). Power output determined at these thresholds was 282.1 +/-4.2, 302.5 +/-1.3, and 296.0 +/- 1.8 W, respectively, whereas HR was determined to be 88.6 +/- 0.01, 92.2 +/- 0.01, and 91.0 +/- 0.01% of maximum, respectively. Power output and HR were significantly lower for LaT than for the other 2 methods (p < 0.05). On separate visits, cyclists were instructed to perform maximum efforts for 30 and 60 minutes (30TT and 60TT). Lactate, HR, perceived exertion (RPE), and metabolic variables were measured during the time trials. During the 30TT, participants sustained a significantly higher lactate level (5.29 +/- 0.3 vs. 3.43 +/- 0.3 mmol.L(-1), p < 0.001), percentage of maximum HR (%HRmax) (90.3 +/- 0.02 vs. 84.6 +/- 0.01, p = 0.009), and overall RPE (15.5 +/- 0.5 vs. 14.4 +/- 0.5, p = 0.009), than during the 60TT. .V(O2) was not significantly different between the time trials; however, .V(CO2) (p = 0.008), ventilation (p = 0.004), and respiratory exchange ratio (p = 0.02) were significantly higher during the 30TT. Correlations were found between HR at LaT (r = 0.78), OBLA (r = 0.78), and Dmax (r = 0.71) for the 60TT, but not for the 30TT. These data suggest that despite a large variability in blood lactate during time trial efforts of 30 and 60 minutes (from 1.8 to 10.8 mmol.L(-1)), HR was consistently 90% of maximum for the 30TT and 85% for the 60TT. HR during the 30TT was approximated by HR corresponding to OBLA and Dmax, whereas HR during 60TT was approximated by LaT.     

Advantages of social foraging in crab spiders: Groups capture more and larger prey despite the absence of a web

Among group‐living spiders, subsocial representatives in the family of crab spiders (Thomisidae) are a special case, as they build protective communal leaf nests instead of extensive communal capture webs. It could thus be inferred that antipredator benefits (e.g., enhanced protection in larger nests) rather than foraging‐related advantages (e.g., capture of more and larger prey) promote sociality in this family. Nonetheless, subsocial crab spiders do share prey, and if this behaviour does not reflect mere food scramble but has a cooperative character, crab spiders may offer insights into the evolution of social foraging applicable to many other cooperative predators that hunt without traps. Here, we performed a comparative laboratory feeding experiment on three of the four subsocial crab spider species—Australomisidia ergandros, Australomisidia socialis and Xysticus bimaculatus—to determine if crab spiders derive advantages from foraging in groups. In particular, we tested artificially composed groups of five sibling spiderlings vs. single siblings in terms of prey capture success and prey size preference. Across species, groups had higher prey capture success (measured in terms of capture rates and capture latency) and were more likely to attack large, sharable prey—dynamics leading to reduced food competition among group members in favour of living and foraging in groups. Within groups, we further compared prey extraction efficiency among the three applied social foraging tactics: producing, scrounging and feeding alone. In A. ergandros, individuals were exceptionally efficient when using the non‐cooperative scrounger tactic, which entails feeding on the prey provided by others. Thus, our multispecies comparison confirms foraging advantages in maintaining a cooperative lifestyle for crab spiders, but also demonstrates the relevance of research into exploitation of cooperative foraging in this family.     

Noncatalytic cGMP-binding sites of amphibian rod cGMP phosphodiesterase control interaction with its inhibitory gamma-subunits. A putative regulatory mechanism of the rod photoresponse.

The cGMP phosphodiesterase (PDE) of retinal rods plays a central role in phototransduction. Illumination leads to its activation by a rod G-protein (Gt, transducin), thus causing a decrease in intracellular cGMP concentration, closure of plasma membrane cationic channels gated by cGMP, and development of the photoresponse. The PDE holoenzyme is an alpha beta gamma 2 tetramer. The alpha- and beta-subunits each contain one catalytic and one, or possibly two, noncatalytic cGMP-binding sites. Two identical gamma-subunits serve as protein inhibitors of the enzyme. Their inhibition is removed when they bind to Gt-GTP during PDE activation. Here we report that the noncatalytic cGMP-binding sites regulate the binding of PDE alpha beta with PDE gamma and as a result determine the mechanism of PDE activation by Gt. If the noncatalytic sites are empty, Gt-GTP physically removes PDE gamma from PDE alpha beta upon activation. Alternatively, if the noncatalytic sites are occupied by cGMP, Gt-GTP releases PDE gamma inhibitory action but remains bound in a complex with the PDE heterotetramer. The kinetic parameters of activated PDE in these two cases are indistinguishable. This mechanism appears to have two implications for the physiology of photoreceptor cells. First, the tight binding of PDE gamma with PDE alpha beta when the noncatalytic sites are occupied by cGMP may be responsible for the low level of basal PDE activity observed in dark-adapted cells. Second, occupancy of the noncatalytic sites ultimately controls the rate of PDE inactivation (cf. Arshavsky, V. Yu., and Bownds, M. D. (1992) Nature 357, 416-417), for the GTPase activity that terminates PDE activity is slower when these sites are occupied and Gt stays in a complex with PDE holoenzyme. In contrast GTPase acceleration is maximal when the noncatalytic sites are empty and Gt-PDE gamma dissociates from PDE alpha beta. Because cGMP levels are known to decrease upon illumination over a concentration range corresponding to the binding constants of the noncatalytic sites, the binding might be involved in determining the lifetime of activated PDE, after a single flash and/or during dark adaptation.     

Carbohydrate supplementation and perceived exertion during resistance exercise

The purpose of the present study was to investigate the relationship between carbohydrate energy substrate and the perception of exertion during resistance exercise. Thirty strength-trained subjects were randomized to a carbohydrate group (C) or a placebo group (P), and lifted weights for 2 hours (4 sets; 10 repetitions maximum; 10 exercises; 2-3-minute rest intervals). Subjects ingested 10 ml.kg(-1).h(-1) of 6% carbohydrate or placebo beverages during the resistance-training bout. The 15-category Borg Perceived Exertion Scale was used to assess overall body (RPE-O) and active muscle (RPE-AM) perceived exertion after completion of the last repetition in each set for each exercise. No significant differences were found between the C and P groups for either RPE-O or RPE-AM, with the exception of RPE-O for the upright row and back squat (p < 0.05). Carbohydrate supplementation exerted no attenuating effect on ratings of perceived exertion (RPE) during resistance training.     

Effect of resistance exercise and carbohydrate ingestion on oxidative stress

Some research studies have produced data indicating that resistance exercise induces oxidative stress, despite minimal increases in VO₂. These studies have primarily relied on oxidative stress markers with low sensitivity and debatable reliability. However, F₂-isoprostanes as measured by gas chromatography mass spectrometry are considered to be a reliable and precise indicator of oxidative stress. Carbohydrate ingestion during exercise is associated with reduced levels of stress hormones, which may influence oxidative stress and plasma antioxidant potential. Therefore, the purpose of this study was to investigate the influence of carbohydrate ingestion during resistance training on F₂-isoprostanes and plasma antioxidant potential. Thirty strength-trained subjects were randomized to carbohydrate (CHO) or placebo (PLA) groups that lifted weights for 2 h. Subjects received 10 ml kg^- 1 h^- 1 CHO (6%) or PLA beverages during the exercise. Blood and vastus lateralis muscle biopsy samples were collected before and after exercise and analyzed for cortisol as a marker of general stress, F₂-isoprostanes as a measure of oxidative stress, and ferric reducing ability of plasma (FRAP) as a measure of antioxidant potential, and for muscle glycogen, respectively. Decreases in muscle glycogen content did not differ between CHO and PLA. Cortisol and FRAP increased significantly in CHO and PLA (P = 0.008 and 0.044, respectively), but the pattern of change was not different between groups. F₂-isoprostanes were unaffected by exercise. These results indicate that exhaustive resistance exercise and carbohydrate ingestion have no effect on oxidative stress or plasma antioxidant potential in trained subjects.     

Trophic complexity of small fish in nearshore food webs

Small nearshore fishes are an important part of lacustrine and functional diversity and link pelagic and benthic habitats by serving as prey for larger nearshore and offshore fishes. However, the trophic complexity of these small nearshore fishes is often unrecognized and detailed studies of their role in food webs are lacking. Here, we examined niche space patterns of small nearshore fish species using Bayesian analyses of carbon and nitrogen stable isotope data in nine freshwater lakes that are among the largest lakes in Minnesota. We found considerable variability in niche areas within species and high variability in niche overlap across species. At the assemblage level, niche overlap (average diet overlap of all species pairs at a lake) decreased as whole-lake species richness increased, possibly indicating a greater degree of resource specialization in more speciose lakes. Overall fish niche space was weakly but significantly related to niche space of their invertebrate prey. Although nearshore benthic resources contributed to fish diets in all lakes, all fish species also had non-negligible and variable contributions from pelagic zooplankton. This inter- and intraspecific variability in trophic niche space likely contributes to the multi-level trophic complexity, functional diversity, and potentially food web resilience to ecosystem changes.