Ventilatory and metabolic responses of burrowing owls, Athene cunicularia, to moderate and extreme hypoxia: analysis of the hypoxic ventilatory threshold vs. hemoglobin oxygen affinity relationship in birds

We measured ventilation, oxygen consumption and blood gases in burrowing owls (Athene cunicularia) breathing moderate and extreme hypoxic gas mixtures to determine their hypoxic ventilatory threshold (HVT) and to assess if they, like other birds and mammals, exhibit a relationship between HVT and hemoglobin O2 affinity (P(50)) of their blood. An earlier report of an attenuated ventilatory responsiveness of this species to hypoxia was enigmatic given the low O2 affinity (high P(50)) of burrowing owl hemoglobin. In the current study, burrowing owls breathing 11% and 9% O2 showed a significantly elevated total ventilation. The arterial partial pressure of oxygen (PaO2) at which ventilation is elevated above normoxic values in burrowing owls was 58 mm Hg. This threshold value conforms well to expectations based on the high P(50) of their hemoglobin and the HVT vs. P(50) relationship for birds developed in this study. Correcting for phylogenetic relatedness in the multi-species analysis had no effect on the HVT vs. P(50) relationship. Also, because burrowing owls in this study did not show a hypometabolic response at any level of hypoxia (even at 9% O2); HVT described in terms of percent change in oxygen convection requirement is identical to that based on ventilation alone.     

Warming and drought alter C and N concentration,allocation and accumulation in a Mediterranean shrubland

We investigated the effects of warming and drought on C and N concentrations, nitrogen use efficiency (NUE), and C and N accumulation in different ecosystem compartments. We conducted a 6-year (1999–2005) field experiment to simulate the climate conditions projected by IPCC models for the coming decades in a Mediterranean shrubland. We studied the two dominant species, Globularia alypum and Erica multiflora, and an N-fixing species, Dorycnium pentaphyllum, also abundant in this shrubland. Warming (1 °C) decreased N leaf concentrations by 25% and increased N stem concentrations by 40% in G. alypum. Although warming changed the available ammonium in soil in some seasons, it did not increase total soil N contents. Drought (19% average reduction in soil moisture) decreased leaf N concentrations in the two dominant shrub species, E. multiflora and G. alypum by 16% and 19%, respectively, and increased stem N concentrations by 56% and 40%, respectively. Neither warming nor drought changed the leaf N concentrations in the N-fixing species D. pentaphyllum, although warming increased stem N concentration by 9%. In G. alypum, the increase of stem N concentrations contributed to the observed increase of N accumulation in stem biomass in drought treatments with respect to control plots (8 kg N ha⁻¹). Neither warming nor drought changed NUE in the period 1999–2005. Warming increased soil organic C relative to drought. The effects of warming and drought on C and N concentrations, on N accumulation and on leaf/stem N distribution were not the result of dilution or concentration effects produced by changes in biomass accumulation. Other factors such as the changes in soil N availability, photosynthetic capacity, and plant internal C and N remobilization must be involved. These changes which differed depending on the species and the plant tissue show that the climate change projected for the coming decades will have significant effects on the C and N cycle and stoichiometry, with probable implications for ecosystem structure and function, such as changes in plant–herbivore relationships, decomposition rates or community species composition.     

DNA from uncultured organisms as a source of 2,5-diketo-D-gluconic acid reductases

Total DNA of a population of uncultured organisms was extracted from soil samples, and by using PCR methods, the genes encoding two different 2,5-diketo-D-gluconic acid reductases (DKGRs) were recovered. Degenerate PCR primers based on published sequence information gave internal gene fragments homologous to known DKGRs. Nested primers specific for the internal fragments were combined with random primers to amplify flanking gene fragments from the environmental DNA, and two hypothetical full-length genes were predicted from the combined sequences. Based on these predictions, specific primers were used to amplify the two complete genes in single PCRs. These genes were cloned and expressed in Escherichia coli. The purified gene products catalyzed the reduction of 2,5-diketo-D-gluconic acid to 2-keto-L-gulonic acid. Compared to previously described DKGRs isolated from Corynebacterium spp., these environmental reductases possessed some valuable properties. Both exhibited greater than 20-fold-higher kcat/Km values than those previously determined, primarily as a result of better binding of substrate. The Km values for the two new reductases were 57 and 67 microM, versus 2 and 13 mM for the Corynebacterium enzymes. Both environmental DKGRs accepted NADH as well as NADPH as a cosubstrate; other DKGRs and most related aldo-keto reductases use only NADPH. In addition, one of the new reductases was more thermostable than known DKGRs.     

Direct evidence that C-peptide inhibitors of human immunodeficiency virus type 1 entry bind to the gp41 N-helical domain in receptor-activated viral envelope

While it has been established that peptides modeling the C-helical region of human immunodeficiency virus type 1 gp41 are potent in vivo inhibitors of virus replication, their mechanism of action has yet to be determined. It has been proposed, but never directly demonstrated, that these peptides block virus entry by interacting with gp41 to disrupt the formation or function of a six-helix bundle structure. Using a six-helix bundle-specific monoclonal antibody with isolate-restricted Env reactivity, we provide the first direct evidence that, in receptor-activated viral Env, C-peptide entry inhibitors bind to the gp41 N-helical coiled-coil to form a peptide/protein hybrid structure and, in doing so, disrupt native six-helix bundle formation.     

Effects of different set configurations on barbell velocity and displacement during a clean pull

The effects of 3 types of set configurations (cluster, traditional, and undulating) on barbell kinematics were investigated in the present study. Thirteen men (track and field = 8; Olympic weightlifters = 5) (mean +/- SEM age, 23.4 +/- 1.1 years; height, 181.3 +/- 2.1 cm; body mass, 89.8 +/- 4.2 kg) performed 1 set of 5 repetitions in a cluster, traditional, and undulating fashion at 90 and 120% of their 1 repetition maximum (1RM) power clean (119.0 +/- 4.3 kg). All data were collected at 50 Hz and analyzed with a V-Scope Weightlifting Analysis System. Peak velocity (PV) and peak displacement (PD) were analyzed for each repetition and averaged for each set type. Results indicated that a significantly (p < 0.016) higher PV occurred during the cluster set when compared with the traditional sets at both intensities. PD was significantly higher than traditional sets at the 120% intensity. The present study suggests set configuration can affect PV and PD during clean pulls.     

Force-time curve characteristics of dynamic and isometric muscle actions of elite women olympic weightlifters

Six elite women weightlifters were tested to evaluate force-time curve characteristics and intercorrelations of isometric and dynamic muscle actions. Subjects performed isometric and dynamic mid-thigh clean pulls at 30% of maximal isometric peak force and 100 kg from a standardized position on a 61.0 x 121.9 cm AMTI forceplate. Isometric peak force showed strong correlations to the athletes' competitive snatch, clean and jerk, and combined total (r = 0.93, 0.64, and 0.80 respectively). Isometric rate of force development showed moderate to strong relationships to the athletes' competitive snatch, clean and jerk, and combined total (r = 0.79, 0.69, and 0.80 respectively). The results of this study suggest that the ability to perform maximal snatch and clean and jerks shows some structural and functional foundation with the ability to generate high forces rapidly in elite women weightlifters.     

Temporal and spatial expression of the period gene in the reproductive system of the codling moth

The authors examined patterns of spatial and temporal expression of Drosophila per gene homologue in the codling moth, Cydia pomonella. Since sperm release in moths is regulated in a circadian manner by an autonomous clock that is independent from the brain, the authors investigated per expression in male reproductive system along with its expression in moth heads. per mRNA is rhythmically expressed with the same phase and amplitude in both tissues under light-dark (LD) conditions. The levels of per mRNA are low during the day, start to increase before lights-off, reach the peak in dark, and decrease after lights-on. In constant darkness (DD), cycling of per mRNA continued in heads with severely blunted amplitude. No cycling of per mRNA was detected in testis in DD. In situ hybridization and immunocytochemistry revealed distinct spatial patterns of per expression in the moth reproductive system. There is no expression of per in cells forming the wall of testes or in sperm bundles. However, per mRNA and protein are rhythmically expressed in the epithelial cells forming the wall of the upper vas deferens (UVD) and in the cells of the terminal epithelium, which are involved in the circadian gating of sperm release. Increase in per mRNA in the UVD coincides with sperm accumulation in this part of the insect reproductive system.     

Simulation of high-frequency sinusoidal electrical block of mammalian myelinated axons

High frequency alternating current (HFAC) sinusoidal waveforms can block conduction in mammalian peripheral nerves. A mammalian axon model was used to simulate the response of nerves to HFAC conduction block. Sinusoidal waveforms from 1 to 40 kHz were delivered to eight simulated axon diameters ranging from 7.3 to 16 μm. Conduction block was obtained between 3 to 40 kHz. The minimum peak to peak current at which block was obtained, defined as the block threshold, increased with increasing frequency. Block threshold varied inversely with axon diameter. Upon initiation, the HFAC waveform produced one or more action potentials. These simulation results closely parallel previous experimental results of high frequency motor block of the rat sciatic and cat pudendal nerve. During HFAC block, the axons showed a dynamic steady state depolarization of multiple nodes, strongly suggesting a depolarization mechanism for HFAC conduction block. Action Editor: Karen Sigvardt     

Anti-AIDS agents 73: structure-activity relationship study and asymmetric synthesis of 3-O-monomethylsuccinyl-betulinic acid derivatives

3-O-3'(or 2')-Methylsuccinyl-betulinic acid (MSB) derivatives were separated by using recycle HPLC. The structures of four isomers were assigned by NMR and asymmetric synthesis. 3-O-3'S-Methylsuccinyl-betulinic acid (3'S-MSB, 4) exhibited potent anti-HIV activity with an EC(50) value of 0.0087microM and a TI value of 6.3x10(3), which is comparable to the data for bevirimat (DSB, PA-457), a current clinical trials drug that was also derived from betulinic acid. The anti-HIV potency of 4 was slightly better than that of AZT.