Repeated high-force eccentric exercise: effects on muscle pain and damage

Five women and three men (aged 24-43 yr) performed maximal eccentric contractions of the elbow flexors (for 20 min) on three occasions, spaced 2 wk apart. Muscle pain, strength and contractile properties, and plasma creatine kinase (CK) were studied before and after each exercise bout. Muscle tenderness was greatest after the first bout and thereafter progressively decreased. Very high plasma CK levels (1,500-11,000 IU/l) occurred after the first bout, but the second and third bouts did not significantly affect the plasma CK. After each bout the strength was reduced by approximately 50% and after 2 wk had only recovered to 80% of preexercise values. Each exercise bout produced a marked shift of the force-frequency curve to the right which took approximately 2 wk to recover. The recovery rate of both strength and force-frequency characteristics was faster after the second and third bouts. Since the adaptation occurred after the performance of maximal contractions it cannot have been a result of changes in motor unit recruitment. The observed training effect of repeated exercise was not a consequence of the muscle becoming either stronger or more resistant to fatigue.     

Distribution of mercury 203 in pregnant rats and their fetuses following systemic infusions with thiol-containing amino acids and glutathione during late gestation

To investigate the effect of amino acids and the tripeptide glutathione (GSH) on tissue uptake of methylmercury (MeHg) in the developing rat fetus in utero, pregnant rats were continuously infused into the external jugular vein with 0.1 mM L-cysteine, 0.1 mM L-leucine, 0.1 mM GSH or saline commencing on day 17 of gestation. This was followed at 24, 48, and 72 hours by external jugular infusion of 50 microM [203Hg]-MeHgCl administered in 1 ml over 1 hour. Pups were surgically removed from the uterus on gestational day 21. Whole body, brain, kidney, liver, and placental 203Hg radioactivity was measured by means of gamma-spectrometry. Brain 203Hg concentration in pups exposed in utero to L-cysteine was significantly higher compared with pups exposed to saline (P less than 0.05). Brain 203Hg concentration in pups exposed in utero to L-leucine and GSH was significantly depressed compared with pups exposed to saline (P less than 0.05). Kidney 203Hg concentration was not significantly changed in all treatment groups compared with controls. Liver 203Hg concentration was significantly depressed in L-leucine- and GSH-treated pups compared with controls (P less than 0.05). Placental 203Hg concentration was not affected by any treatment compared with controls. These effects occurred despite no difference in total 203Hg body burden among pups, irrespective of the treatment. In addition, infusion with L-cysteine resulted in a significant increase in 203Hg brain concentration in dams compared with controls, and 203Hg brain concentration in L-leucine- and GSH-treated dams was significantly depressed compared with controls. Thus 203Hg distribution in both adult and developing animals is altered by chronic amino acid or GSH infusions and suggests that MeHg uptake may be mediated through the formation of a cysteine-MeHg complex which is transported across the blood-brain barrier by the neutral amino acid carrier transport system.     

Extracellular matrix disruption and pain after eccentric muscle action

Pain, stiffness, and indicators of muscle damage occur at different times after eccentric muscle action. After a single bout of maximal resisted lengthening of the elbow flexors, elbow position, pain perception, and indicators of cellular damage were measured. Immediately postexercise, a significant decrease in resting muscle length was observed that continued to 48 h. At this time, an increase in perceived muscle soreness was noted (P less than 0.05), and a biopsy of the biceps brachii revealed mast cell degranulation, separations of the extracellular matrix from myofibers, and increased plasma constituents in the extracellular space. It is proposed that myofiber disruption allows intracellular proteins to escape and extracellular proteins and ions to enter, causing swelling, whereas the disrupted extracellular matrix initiates the inflammatory response, which includes the release of mast cell granules seen at 48 h postexercise. Thus the delayed sensation of pain (soreness) after repeated eccentric muscle actions probably results from inflammation in response to extracellular matrix disruption.     

The regeneration and screening of watercress somaclones for resistance to Spongospora subterranea f. sp. nasturtii and measurement of somaclonal variation

A range of watercress (Rorippa nasturtium-aquaticum) explants (stems, hypocotyls, true-leaves, cotyledons and petioles) were tested for their capacity to regenerate adventitious shoots from callus formed using Murashige and Skoog medium containing different concentrations of thidiazuron and 2,4-dichlorophenoxyacetic acid. The highest shoot regeneration rate was a mean of 18 shoots per responding explant from stem callus formed on medium containing 5 μM thidiazuron and 0.05 μM 2,4-dichlorophenoxyacetic acid. A histological study confirmed that shoots originated directly from callus tissue. Twenty five percent of somaclones exhibited somaclonal variation in leaf shape, plant height, axillary branching or ploidy. The variation in 6% of somaclones was heritable to the first selfed generation. A screening protocol was developed to permit the identification of somaclones with increased resistance to the economically damaging watercress root pathogen, Spongospora subterranea f. sp. nasturtii. Although 883 somaclones were screened using this protocol, no significant increase in disease resistance was detected. This revised version was published online in June 2006 with corrections to the Cover Date.     

Conformational study of bovine lactoferricin in membrane-micking conditions by molecular dynamics simulation and circular dichroism

Lactoferricins are potent antimicrobial peptides released by pepsin cleavage of Lactoferrins. Bovine Lactoferricin (LfcinB) has higher activity than the intact bovine Lactoferrin, and is the most active among the other Lactoferricins of human, murine and caprine origin. In the intact protein the fragment corresponding to LfcinB is in an helical conformation, while in water LfcinB adopts an amphipathic β-hairpin structure. However, whether any of these structural motifs is the antibacterial active conformation, i.e., the one interacting with bacterial membrane components, remains to be seen. Here we present Circular Dichroism (CD) spectra and Molecular Dynamics (MD) simulations indicating that in membrane-mimicking solvents the LfcinB adopts an amphipathic β-hairpin structure similar to that observed in water, but differing in the dynamic behavior of the side-chains of the two tryptophan residues. In the membrane-mimicking solvent these side-chains show a high propensity to point towards the hydrophobic environment, rather than being in the hydrophobic core as seen in water, while the backbone preserves the hairpin conformation as found in water. These results suggest that the tryptophans might act as anchors pulling the stable, solvent-invariant hairpin structure into the membrane.