Correlations between a nuclear and a mitochondrial mRNA of cytochrome c oxidase subunits,enzymatic activity and total mRNA content,in rat tissues

Summary Cytochrome c oxidase (COX), like other multi-subunit components of the respiratory chain, is controlled by both the nuclear and the mitochondrial genome. In order to find wether there is a close relationship between mRNAs encoded by the nucleus and by the mitochondrion, and between these mRNAs and enzyme activity, we compared six rat tissues (ventricle, liver, m. soleus, m. plantaris, and the white and red portions of m. gastrocnemius). We found a tenfold range for COX activity, a tenfold range for the contents of mRNA III (mitochondrial) and mRNA VIc (nuclear), a threefold range for total [poly(A)⁺] mRNA content and a sevenfold range for total RNA content in these tissues. The ratio of mRNA III to mRNA VIc was equal in each tissue, indicating the presence of a mechanism that coordinates the two genomes. There was a good correlation between mRNA content and COX activity (r = 0.78 for VIc, r = 0.77 for 111; p < 0.0001), demonstrating that the expression of this enzyme is mainly under pretranslational control.     

DELAYED URIC ACID ACCUMULATION IN PLASMA PROVIDES ADDITIONAL ANTI-OXIDANT PROTECTION AGAINST IRON-TRIGGERED OXIDATIVE STRESS AFTER A WINGATE TEST

Reactive oxygen species are produced during anaerobic exercise mostly by Fe ions released into plasma and endothelial/muscle xanthine oxidase activation that generates uric acid (UA) as the endpoint metabolite. Paradoxically, UA is considered a major antioxidant by virtue of being able to chelate pro-oxidative iron ions. This work aimed to evaluate the relationship between UA and plasma markers of oxidative stress following the exhaustive Wingate test. Plasma samples of 17 male undergraduate students were collected before, 5 and 60 min after maximal anaerobic effort for the measurement of total iron, haem iron, UA, ferric-reducing antioxidant activity in plasma (FRAP), and malondialdehyde (MDA, biomarker of lipoperoxidation). Iron and FRAP showed similar kinetics in plasma, demonstrating an adequate pro-/antioxidant balance immediately after exercise and during the recovery period (5–60 min). Slight variations of haem iron concentrations did not support a relevant contribution of rhabdomyolysis or haemolysis for iron overload following exercise. UA concentration did not vary immediately after exercise but rather increased 29% during the recovery period. Unaltered MDA levels were concomitantly measured. We propose that delayed UA accumulation in plasma is an auxiliary antioxidant response to post-exercise (iron-mediated) oxidative stress, and the high correlation between total UA and FRAP in plasma (R-Square = 0.636; p = 0.00582) supports this hypothesis.     

Potential for strength and endurance training to amplify endurance performance

The impact of adding heavy-resistance training to increase leg-muscle strength was studied in eight cycling- and running-trained subjects who were already at a steady-state level of performance. Strength training was performed 3 days/wk for 10 wk, whereas endurance training remained constant during this phase. After 10 wk, leg strength was increased by an average of 30%, but thigh girth and biopsied vastus lateralis muscle fiber areas (fast and slow twitch) and citrate synthase activities were unchanged. Maximal O2 uptake (VO2max) was also unchanged by heavy-resistance training during cycling (55 ml.kg-1.min-1) and treadmill running (60 ml.kg-1.min-1); however, short-term endurance (4-8 min) was increased by 11 and 13% (P less than 0.05) during cycling and running, respectively. Long-term cycling to exhaustion at 80% VO2max increased from 71 to 85 min (P less than 0.05) after the addition of strength training, whereas long-term running (10 km times) results were inconclusive. These data do not demonstrate any negative performance effects of adding heavy-resistance training to ongoing endurance-training regimens. They indicate that certain types of endurance performance, particularly those requiring fast-twitch fiber recruitment, can be improved by strength-training supplementation.     

Two-Species Migration and Clustering in Two-Dimensional Domains

We extend two-species models of individual aggregation or clustering to two-dimensional spatial domains, allowing for more realistic movement of the populations compared with one spatial dimension. We assume that the domain is bounded and that there is no flux into or out of the domain. The motion of the species is along fitness gradients which allow the species to seek out a resource. In the case of competition, species which exploit the resource alone will disperse while avoiding one another. In the case where one of the species is a predator or generalist predator which exploits the other species, that species will tend to move toward the prey species, while the prey will tend to avoid the predator. We focus on three primary types of interspecies interactions: competition, generalist predator–prey, and predator–prey. We discuss the existence and stability of uniform steady states. While transient behaviors including clustering and colony formation occur, our stability results and numerical evidence lead us to believe that the long-time behavior of these models is dominated by spatially homogeneous steady states when the spatial domain is convex. Motivated by this, we investigate heterogeneous resources and hazards and demonstrate how the advective dispersal of species in these environments leads to asymptotic steady states that retain spatial aggregation or clustering in regions of resource abundance and away from hazards or regions or resource scarcity.     

Growth dynamics of Agrobacterium tumefaciens in chemostat cultures limited by carbon source and mineral nutrients.

Agrobacterium tumefaciens was grown in a chemostat in a chemically-defined medium which hs alpha-methyl D-glucoside, magnesium, manganese, phosphate or urea as the growth-limiting nutrient. Steady-state biomass concentrations were dependent on the specific growth rate of the organism when alpha-methyl D-glucoside, manganese or phosphate were growth-limiting nutrients. During magnesium-limited growth, large undamped oscillations in biomass concentration occurred. In all chemostat cultures a variant organism was selected which had lost the ability to grow in the medium supplied, bur survived on products of carbon metabolism derived from the wild-type.     

Polymyxin B inhibits contraction-stimulated glucose uptake in rat skeletal muscle

Glucose transport in muscle is activated by contractile activity, an effect that persists in the postexercise state. Polymyxin B, a cyclic decapeptide antibiotic, inhibits the stimulation of glucose uptake in isolated muscle by contractile activity but also decreases tension development in electrically stimulated muscle. The purpose of this study was to determine whether polymyxin B also inhibits contraction-stimulated glucose uptake after in vivo administration of the drug and to examine the relationship between the effects of polymyxin B on tension development and its effects on contraction-stimulated glucose uptake. When polymyxin B was administered to rats in vivo, glucose uptake in muscle after electrical stimulation was decreased, despite the same amount of tension developed as in control rats, indicating an effect of polymyxin B on glucose transport independent of tension development. Our results also indicate that the postexercise increase in glucose uptake is a function of the tension developed by prior contractions. When muscles were perfused with medium containing polymyxin B, this relationship was disrupted. These results provide evidence that polymyxin B causes a decrease in muscle glucose uptake independent of its effects on tension development. The extent to which its effects on glucose uptake are also the result of a diminution in contractile force is uncertain.