Nuclear Overhauser experiments at 500 MHz on the downfield proton spectrum of a ribonuclease-resistant fragment of 5S ribonucleic acid

The downfield (9-15 ppm) proton NMR spectrum of a RNase A resistant fragment of E. coli 5S RNA has been studied by nuclear Overhauser methods. The fragment comprises bases 1-11 and 69-120 of the parent molecule [Douthwaite, S., Garrett, R.A., Wagner, R., & Feunteun, J. (1979) Nucleic Acids Res. 6, 2453-2470]. The nuclear Overhauser data identify two double helical structures in the fragment whose sequences are (GC)3(AU)(GC)3 and (GC)2(AU)(GU). These structures correspond exactly to the central portions of the terminal stem and procaryotic loop helices which should exist in the fragment sequences according to the Fox-Woese model [Fox, G.E., & Woese, C. R. (1975) Nature (London) 256, 505-506] of 5S RNA secondary structure. The significance of these and other nuclear Overhauser effects detected for the structure of 5S RNA and its fragment is discussed.     

Muscle oxidative metabolism accelerates with mild acidosis during incremental intermittent isometric plantar flexion exercise

BACKGROUND: It has been thought that intramuscular ADP and phosphocreatine (PCr) concentrations are important regulators of mitochondorial respiration. There is a threshold work rate or metabolic rate for cellular acidosis, and the decrease in muscle PCr is accelerated with drop in pH during incremental exercise. We tested the hypothesis that increase in muscle oxygen consumption (o2mus) is accelerated with rapid decrease in PCr (concomitant increase in ADP) in muscles with drop in pH occurs during incremental plantar flexion exercise. METHODS: Five male subjects performed a repetitive intermittent isometric plantar flexion exercise (6-s contraction/4-s relaxation). Exercise intensity was raised every 1 min by 10% maximal voluntary contraction (MVC), starting at 10% MVC until exhaustion. The measurement site was at the medial head of the gastrocnemius muscle. Changes in muscle PCr, inorganic phosphate (Pi), ADP, and pH were measured by 31P-magnetic resonance spectroscopy. o2mus was determined from the rate of decrease in oxygenated hemoglobin and/or myoglobin using near-infrared continuous wave spectroscopy under transient arterial occlusion. Electromyogram (EMG) was also recorded. Pulmonary oxygen uptake (o2pul ) was measured by the breath-by-breath gas analysis. RESULTS: EMG amplitude increased as exercise intensity progressed. In contrast, muscle PCr, ADP, o2mus, and o2pul did not change appreciably below 40% MVC, whereas above 40% MVC muscle PCr decreased, and ADP, o2mus, and o2pul increased as exercise intensity progressed, and above 70% MVC, changes in muscle PCr, ADP, o2mus, and o2pul accelerated with the decrease in muscle pH (~6.78). The kinetics of muscle PCr, ADP, o2mus, and o2pul were similar, and there was a close correlation between each pair of parameters (r = 0.969~0.983, p < 0.001). CONCLUSION: With decrease in pH muscle oxidative metabolism accelerated and changes in intramuscular PCr and ADP accelerated during incremental intermittent isometric plantar flexion exercise. These results suggest that rapid changes in muscle PCr and/or ADP with mild acidosis stimulate accelerative muscle oxidative metabolism.     

Discrepancy between cardiorespiratory system and skeletal muscle in elite cyclists after hypoxic training

BACKGROUND: The purpose of this study was to determine the effects of hypoxic training on the cardiorespiratory system and skeletal muscle among well-trained endurance athletes in a randomized cross-over design. METHODS: Eight junior national level competitive cyclists were separated into two groups; Group A trained under normoxic condition (21% O2) for 2 hours/day, 3 days/week for 3 weeks while Group B used the same training protocol under hypoxic condition (15% O2). After 3 weeks of each initial training condition, five weeks of self-training under usual field conditions intervened before the training condition was switched from NT to HT in Group A, from HT to NT in Group B. The subjects were tested at sea level before and after each training period. O2 uptake (O2), blood samples, and muscle deoxygenation were measured during bicycle exercise test. RESULTS AND DISCUSSION: No changes in maximal workload, arterial O2 content, O2 at lactate threshold and O2max were observed before or after each training period. In contrast, deoxygenation change during submaximal exercise in the vastus lateralis was significantly higher at HT than NT (p < 0.01). In addition, half time of oxygenation recovery was significantly faster after HT (13.2 PlusMinus; 2.6 sec) than NT (18.8 PlusMinus; 2.7 sec) (p < 0.001). CONCLUSIONS: Three weeks of HT may not give an additional performance benefit at sea level for elite competitive cyclists, even though HT may induce some physiological adaptations on muscle tissue level.     

Nuclear Overhauser experiments at 500 MHz on the downfield proton spectra of 5S ribonucleic acid and its complex with ribosomal protein L25

The downfield (9-15 ppm) proton spectrum of Escherichia coli 5S RNA has been examined at 500 MHz by using nuclear Overhauser methods. The data confirm the existence of the terminal and procaryotic loop helices within the molecule [Fox, G. E., & Woese, C. R. (1975) Nature (London) 256, 505-506]. Very little stable, double-helical structure is detectable in the third loop of the molecule, the one comprising bases 12-68. The downfield spectrum of 5S RNA is perturbed in a highly specific manner upon addition of protein L25 to the system. The changes seen strongly suggest that the binding site for L25 on 5S RNA includes the procaryotic loop helix, but not the terminal stem helix. Similar complexes formed between L25 and the 5S RNA fragment consisting of bases 1-11, 69-87, and 89-120 show exactly the same spectral alterations. A number of downfield resonances appear in the spectra of these complexes which have no counterparts in the free RNA, suggesting the stabilization of new RNA structures by the protein. There are some indications of protein-nucleic acid nuclear Overhauser effects.     

Quality control of refrigerated and cryopreserved semen using computer-assisted sperm analysis (CASA), viable staining and standardized fertilization in African catfish (Clarias gariepinus)

A new integrated approach including computer-assisted sperm analysis (CASA), viability staining and fertilization was used to study the quality of cryodiluents used in fish sperm cryopreservation. As an example the sperm quality of an African catfish, Clarias gariepinus (Burchell, 1822), was assessed by its fertilizing ability, motility and viability at day 0 (fresh), after 2 days' storage at 4 degreesC and after 2 days, 5 months and 10 months frozen at -196 degreesC using solutions containing dimethyl sulphoxide (DMSO) or glycerol as permeating cryoprotectants. Four of the best freezing solutions were used, namely, Steyn's extender (S1, S4) and Mounib's extender (M3, M4) associating 10% hen's egg yolk. Progressive sperm movement measured by CASA and expressed by the straight line velocity (VSL), the average path velocity (VAP) and the curvilinear velocity (VCL) was highly correlated with hatching rates obtained from fertilization using minimal sperm:egg ratios. After 2 days, the motility of spermatozoa frozen with DMSO and 10% egg yolk had deteriorated less than that of spermatozoa stored at 4 degreesC. Post-thaw hatching rates reflected the post-thaw sperm viability, which was cryodiluent dependent: 14.9+/-2.0% (S4), 17.0+/-4.2% (S1), 25.9+/-3.7% (M4) and 52.1+/-3.4% (M3) after 5 months of cryopreservation. The percent motility of 10-months-frozen spermatozoa was high in M3 (70.7+/-11.4%) and M4 (64.0+/-2.0%) cryoprotected sperm when measured between 5 and 20 sec after activation, but decreased rapidly to 24.3+/-8.3% (M3) and 23.0+/-9.0% (M4) between 21 and 35 sec after activation. Mounib's extender (M3, M4) provided the best cryoprotection to the spermatozoa for all post-thaw sperm quality measurements and at all freezing durations. Sperm motility was positively related to fertility. Our method will make it possible to develop even better extenders and cryoprotectants.     

The transmission of advertisement calls in Central American frogs

Acoustic communication signals change over distance due to lossof amplitude and fidelity, and it is assumed that signal degradationinfluences the receiver's ability to detect and decode signals.The degree of degradation depends on the signal's structureand the environment through which it transmits. We broadcastthe advertisement calls of 22 species of Central American frogsat two heights within forested and open environments in Panama. Werecorded these calls at five distances from the source and estimatedsignal degradation with a cross-correlation analysis, a measurethat combines the effects of decrement in signal amplitude andfidelity. Calls degraded less when broadcast higher above theground compared to on the ground, and less in open habitat comparedto forested habitat; there was an additional interaction betweenheight and environment. Furthermore, calls with low dominant frequenciesexperienced less degradation than calls with high dominant frequencies.There was no evidence, however, that the calls of these frogs haveevolved to maximize habitat-specific transmission.