We addressed the need for histological assessment of myocellular domains occupied by monocarboxylate transporters (MCT1, MCT2 and MCT4). From the perspective of lactate shuttle hypotheses we posited that MCT1 would be highly expressed in oxidative fibres, whereas MCT4 would be found in highly glycolytic fibres. Furthermore, we hypothesized that MCT1 would be detected at interfibrillar as well as at subsarcolemmal and sarcolemmal cell domains, whereas MCT2 and MCT4 abundances would be most prominent at the sarcolemma. To test these hypotheses, we examined cellular locations of MCT1, MCT2 and MCT4 transporter proteins in different fibre types (slow oxidative, SO; fast oxidative glycolytic, FOG; fast glycolytic, FG) in rat plantaris muscles by the avidin-biotin complex (ABC) as well as other methods. The plantaris was used as it is a mixed fibre skeletal muscle. MCTs, glucose transporter (GLUT4) protein, and mitochondrial constituent cytochrome oxidase (COX) abundances were assessed by immunohistochemistry and Western blotting using affinity-purified antibodies. The staining method was specific and stable, which allowed for semiquantitative assessment of MCT expression. As well, confocal laser scanning microscopy assessed MCT isoform localizations. Findings of the present study were: (1) MCT1 is located at the sarcolemma and throughout the cell interior in SO and FOG fibres where the mitochondrial reticulum was present; (2) in contrast, MCT4 was highly expressed in the sarcolemmal domain of FG and FOG fibres but poorly expressed in SO fibres; and (3) confocal laser-scanning microscopy demonstrated that MCT1 and COX are co-localised at both interfibrillar and subsarcolemmal cell domains, whereas MCT2 is only faintly detected at the sarcolemma of oxidative fibres. MCTs and associated proteins are positioned to facilitate the function of the lactate shuttles.

No abstract

No abstract

No abstract

Twelve male Sprague-Dawley rats (21 days old) were randomly assigned into two experimental groups: sea level control (CONT) and hypobaric hypoxia (HYPO). The HYPO rats were kept in an hypobaric chamber maintaining a simulated altitude of 4000 m (61.1 kPa). After 10 weeks of treatment, the rat hindlimb muscles [soleus (SOL) and extensor digitorum longus (EDL)] were subjected to histochemical and electro-mechanical analyses. Results indicated that compared to CONT the HYPO SOL muscle had a significantly greater relative distribution of fast-twitch-oxidative-glycolytic (FOG) fibres (28.9% SEM 2.0 vs 18.3% SEM 1.8, P less than 0.01) with a significant decrease in slow twitch oxidative fibre distribution (69.5% SEM 2.4 vs 82.9% SEM 3.1, P less than 0.01). Compared to CONT the HYPO EDL muscle also manifested a significant increase in FOG fibre distribution (51.6% SEM 0.8 vs 46.6% SEM 1.1, P less than 0.01), but this was accompanied by a significant decrease in fast twitch glucolytic fibres (44.3% SEM 0.9 vs 49.2% SEM 1.7, P less than 0.05). These histochemical fibre type transformations accompanied significant and expected changes in the electro-mechanical parameters tested in situ, e.g. maximal twitch force, maximal rate of force development, contraction time, half relaxation time, force: frequency curve, and fatigability. It was concluded that chronic hypobaric hypoxia could have a potent influence upon the phenotype expression of muscle fibres.

No abstract

A rarefied gas flow thermally induced around a heated (or cooled) flat plate, contained in a vessel, is considered in two different situations: (i) both sides of the plate are simultaneously and uniformly heated (or cooled); and (ii) only one side of the plate is uniformly heated. The former is known as the thermal edge flow and the latter, typically observed in the Crookes radiometer, may be called the radiometric flow. The steady behaviour of the gas induced in the container is investigated on the basis of the Bhatnagar-Gross-Krook (BGK) model of the Boltzmann equation and the diffuse reflection boundary condition by means of an accurate finite-difference method. The flow features are clarified for a wide range of the Knudsen number, with a particular emphasis placed on the structural similarity between the two flows. The limiting behaviour of the flow as the Knudsen number tends to zero (and thus the system approaches the continuum limit) is investigated for both flows. The detailed structure of the normal stress on the plate as well as the cause of the radiometric force (the force acting on the plate from the hotter to the colder side) is also clarified for the present infinitely thin plate.

No abstract