Sadayoshi Taguchi

Immunohistochemical analysis of MCT1, MCT2 and MCT4 expression in rat plantaris muscle

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.

Hypoxia-induced fibre type transformation in rat hindlimb muscles. Histochemical and electro-mechanical changes.

SummaryTwelve 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<0.01) with a significant decrease in slow twitch oxidative fibre distribution (69.5% SEM 2.4 vs 82.9% SEM 3.1,P<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<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<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.

Retrograde neuronal labeling of motoneurons in the rat by fluorescent tracers, and quantitative analysis of oxidative enzyme activity in labeled neurons

Extensor digitorum longus motoneurons in the rat spinal cord were identified by retrograde labeling with two fluorescent tracers, Fast blue (FB) and Nuclear yellow (NY). Labeled motoneurons had a blue fluorescent cytoplasm at 360 nm excitation wavelength with FB, and a golden-yellow fluorescent nucleus with NY on the cryostat section. Labeled motoneurons were further examined for succinate dehydrogenase activity on the same section used for identification of the motoneurons. This study demonstrates that fluorescent dyes are useful for neuroanatomical studies by the retrograde axonal transport method, and that quantitative analysis of metabolic activity in labeled motoneurons is also possible.

Air Pollution, Exercise, and Heat Stress

Twenty young men, smokers and non- smokers, were tested for maximal aerobic power in a 35 C environment under four ambient air conditions: (1) filtered air (FA), (2) 50 ppm carbon monoxide (CO), (3) 0.27 ppm peroxyacetyl nitrate (PAN), and (4) CO plus PAN. Carbon monoxide was effective in reducing the work time of the nonsmokers and in eliciting changes In the respiratory patterns of both smokers and nonsmokers. No significant physiological effects were noted during the PAN exposure. Maximal aerobic power was not affected by any pollutant condition. Since the concentrations of CO represented a first-stage alert level for the Los Angeles area, it appears that the air pollution standard for this pollutant is set at a realistic level for healthy young men doing strenuous work for a relatively short period of time.

Oxidative metabolism of the rat soleus neuron pool following hypobaric hypoxia

After 7 weeks of hypoxic acclimation, oxidative enzyme (succinate dehydrogenase) activity of motoneurons in the rat soleus neuron pool was examined. Although the total oxidative metabolism of the neuron pool was not changed, the oxidative enzyme activity of small to medium sized (25-45 microns average soma diameter) alpha motoneurons was increased. These results indicate that hypoxia preferentially enhances the oxidative capacity of specific motoneurons in the neuron pool.

Effects of Hypobaric Hypoxia on the Oxidative Capacity of the Extensor Digitorum Longus Motor Units in the Rat

The fiber number, fiber type distribution, and succinate dehydrogenase activity were investigated from the fast-twitch extensor digitorum longus muscle of male rats exposed to 7 weeks of hypobaric hypoxia. The oxidative metabolic capacity of the motoneurons in the extensor digitorum longus neuron pool was also determined from quantitative histochemical analyses. The fiber number and oxidative enzyme activity of the muscle were not changed by hypoxia. An increase in the percentage of fast-twitch oxidative (FO) fibers and a concemitant decrease in the percentage of fast-twitch (F) fibers were observed in the hypoxic muscle. On the other hand, the oxidative capacity of small-to medium-sized alpha motoneurons (25–45 μm average soma diameter) was increased. The increase in the oxidative capacity of small- to medium-sized motoneurons and the type shift of muscle fibers from F (low-oxidative) to FO (high-oxidative) indicate that hypoxia enhances the oxidative capacity of particular motor units in the neuron pool.

Alterations in the expression of myosin heavy chain isoforms in hypoxia-induced hypertrophied ventricles in rats

This study was designed to characterize cardiac changes in myosin heavy chain (MHC)-beta, capacity for oxidative metabolism and muscle mass in hearts of rats born and raised at simulated altitudes (2200 m or 4000 m) compared to age-matched sea level controls. On the basis of electrophoretic analyses, we found that the hypoxia-induced ventricular hypertrophy produces a significant increase in MHC-beta in both ventricles. Furthermore, we observed an exponential relationship between the mass of right ventricular muscle and percentages in the expression of MHC-beta (r=0.928, P<0.001). We also observed the reduction in the citrate synthase (CS) and 3-hydroxyacyl-CoA dehydrogenase (HAD) activities in both hypertrophied ventricles (P<0.001). As a consequence, there were negative correlations between the percentage expression of MHC-beta and the CS or HAD activities (P<0.001). In contrast, there were no significant correlations between the relative expressions of MHC-beta and either CS or HAD enzymatic activities in both ventricles after adjusting for the relative wet mass. In conclusion, the observed increases in MHC-beta may be a compensation to augment efficiency if muscles contract in hypertrophied hearts where mitochondria fail to respond to increases in tissue mass. These findings suggest that the increased relative expression of MHC-beta is a compensation to sustain cardiac contractile efficiency in response to impaired oxidative metabolism in the hypoxia-induced hypertrophied ventricles of rats.

Metabolic responses to light arm and leg exercise when sitting.

SummarySeven male subjects performed progressive exercises with a light work load on an upper limb or bicycle ergometer in the sitting position. At any comparable work load above zero, arm exercise induced higher oxygen uptake, ventilation, heart rate, oxygen pulse, respiratory rate and tidal volume than leg exercise. At similar levels of

Spaceflight and Biohistochemical Alterations of Antigravity Soleus Musclein Spontaneously Hypertensive Rats (SHR) to Dietary Low and High-Calcium Intake

\dot V_{{\text{O}}_{\text{2}} }