Janusz Karasinski

Myoglobin (Mb) plays an important role at rest and during exercise as a reservoir of oxygen and has been suggested to regulate NO^• bioavailability under hypoxic/acidic conditions. However, its ultimate role during exercise is still a subject of debate. We aimed to study the effect of Mb deficiency on maximal oxygen uptake () and exercise performance in myoglobin knockout mice (Mb^−/−) when compared to control mice (Mb^+/+). Furthermore, we also studied NO^• bioavailability, assessed as nitrite (NO₂⁻) and nitrate (NO₃⁻) in the heart, locomotory muscle and in plasma, at rest and during exercise at exhaustion both in Mb^−/− and in Mb^+/+ mice. The mice performed maximal running incremental exercise on a treadmill with whole‐body gas exchange measurements. The Mb^−/− mice had lower body mass, heart and hind limb muscle mass (P < 0.001). Mb^−/− mice had significantly reduced maximal running performance (P < 0.001). expressed in ml min⁻¹ in Mb^−/− mice was 37% lower than in Mb^+/+ mice (P < 0.001) and 13% lower when expressed in ml min⁻¹ kg body mass⁻¹ (P = 0.001). Additionally, Mb^−/− mice had significantly lower plasma, heart and locomotory muscle NO₂⁻ levels at rest. During exercise NO₂⁻ increased significantly in the heart and locomotory muscles of Mb^−/− and Mb^+/+ mice, whereas no significant changes in NO₂⁻ were found in plasma. Our study showed that, contrary to recent suggestions, Mb deficiency significantly impairs and maximal running performance in mice. image Key points: Myoglobin knockout mice (Mb^−/−) possess lower maximal oxygen uptake () and poorer maximal running performance than control mice (Mb^+/+). Respiratory exchange ratio values at high running velocities in Mb^−/− mice are higher than in control mice suggesting a shift in substrate utilization towards glucose metabolism in Mb^−/− mice at the same running velocities. Lack of myoglobin lowers basal systemic and muscle NO^• bioavailability, but does not affect exercise‐induced NO₂⁻ changes in plasma, heart and locomotory muscles. The present study demonstrates that myoglobin is of vital importance for and maximal running performance as well as explains why previous studies have failed to prove such a role of myoglobin when using the Mb^−/− mouse model.

Skeletal muscles are an important reservoir of nitric oxide (NO^•) stored in the form of nitrite [NO₂⁻] and nitrate [NO₃⁻] (NO_x). Nitrite, which can be reduced to NO^• under hypoxic and acidotic conditions, is considered a physiologically relevant, direct source of bioactive NO^•. The aim of the present study was to determine the basal levels of NO_x in striated muscles (including rat heart and locomotory muscles) with varied contents of tissue nitrite reductases, such as myoglobin and mitochondrial electron transport chain proteins (ETC-proteins). Muscle NO_x was determined using a high-performance liquid chromatography-based method. Muscle proteins were evaluated using western-immunoblotting. We found that oxidative muscles with a higher content of ETC-proteins and myoglobin (such as the heart and slow-twitch locomotory muscles) have lower [NO₂⁻] compared to fast-twitch muscles with a lower content of those proteins. The muscle type had no observed effect on the [NO₃⁻]. Our results demonstrated that fast-twitch muscles possess greater potential to generate NO^• via nitrite reduction than slow-twitch muscles and the heart. This property might be of special importance for fast skeletal muscles during strenuous exercise and/or hypoxia since it might support muscle blood flow via additional NO^• provision (acidic/hypoxic vasodilation) and delay muscle fatigue.

Genetically modified pigs lacking Galα1 → 3Gal and other immunogenic carbohydrates are considered as the most promising, alternative source of various tissues and organs for human transplantation. Here, we tested the hypothesis that combining the expression of human α1,2-fucosyltransferase (hFUT2) and α-galactosidase A (hGLA) genes would allow for the removal of this specific carbohydrate in porcine transgenic livers. We investigated the expression profile of human α1,2-fucosyltransferase and α-galactosidase A proteins and the amount of Galα1 → 3Gal antigen in the liver of single transgenic hFUT2 (n=5), hGLA (n=5), and double transgenic hFUT2 × hGLA (n=5) pigs. Both human proteins, α1,2-fucosyltransferase and α-galactosidase A, were abundantly expressed in the liver tissue in respective transgenic lines as was revealed by confocal microscopy and Western blotting. The level of Galα1 → 3Gal epitope evaluated by lectin histochemistry and lectin blotting was significantly lower (pFUT2 × hGLA indeed improves the removal of the Galα1 → 3Gal epitope in porcine liver. However, this modification alone is not sufficient enough for complete elimination of this antigen from porcine liver tissue.

This study shows that long‐lasting physical exercise does not increase the risk of the progression of the BMP4–mediated pathological cardiac hypertrophy. Moreover, assuming the pro‐inflammatory funct...

Contents: Mammalian uterus contains a population of mesenchymal stem/progenitor cells that likely contribute to endometrial regeneration during each reproductive cycle. In human and mouse, they reside in perivascular, epithelial and stromal compartments of the endometrial functionalis and basalis. Here, we aimed to identify tissue resident cells expressing mesenchymal stem cell markers CD29, CD44, CD90, CD105, CD140b and CD146 in the porcine endometrium. We used single immunofluorescence and Western blotting. Each of these markers was detected in small cells surrounding endometrial blood vessels. CD105 and CD146 were also expressed in single stromal cells. A few stromal and perivascular cells showed the presence of pluripotency marker Oct4 in the cytoplasm, but not in the nucleus, which may imply they are not truly pluripotent. Endometrial cell cultures were examined for the expression of CD29, CD44, CD90, CD105 and CD140b proteins and tested in wound‐healing assay and culture model of chemotaxis. In conclusion, our results demonstrate perivascular location of prospective mesenchymal stem/progenitor cells in the porcine endometrium and may suggest that stromal CD105⁺ and CD146⁺ cells represent more mature precursors originating from their perivascular ancestors.

Dynamic resistance training increases the force and speed of muscle contraction, but little is known about modifications to the contractile properties of the main physiological types of motor units (MUs) that contribute to these muscle adaptations. Although the contractile profile of MU muscle fibers is tightly coupled to myosin heavy chain (MyHC) protein expression, it is not well understood if MyHC transition is a prerequisite for modifications to the contractile characteristics of MUs. In this study, we examined MU contractile properties, the mRNA expression of MyHC, parvalbumin, and sarcoendoplasmic reticulum Ca²⁺pump isoforms, as well as the MyHC protein content after 5 wk of volitional progressive weight-lifting training in the medial gastrocnemius muscle in rats. The training had no effect on MyHC profiling or Ca²⁺-handling protein gene expression. Maximum force increased in slow (by 49%) and fast (by 21%) MUs. Within fast MUs, the maximum force increased in most fatigue-resistant and intermediate but not most fatigable MUs. Twitch contraction time was shortened in slow and fast fatigue-resistant MUs. Twitch half-relaxation was shortened in fast most fatigue-resistant and intermediate MUs. The force-frequency curve shifted rightward in fast fatigue-resistant MUs. Fast fatigable MUs fatigued less within the initial 15 s while fast fatigue-resistant units increased the ability to potentiate the force within the first minute of the standard fatigue test. In conclusion, at the early stage of resistance training, modifications to the contractile characteristics of MUs appear in the absence of MyHC transition and the upregulation of Ca²⁺-handling genes.

In this study we have examined the effect of prolonged endurance training program on the pulmonary oxygen uptake (V’O₂) kinetics during heavy-intensity cycling-exercise and its impact on maximal cycling and running performance. Twelve healthy, physically active men (mean±SD: age 22.33±1.44 years, V’O_2peak 3198±458 mL ∙ min^-1) performed an endurance training composed mainly of moderate-intensity cycling, lasting 20 weeks. Training resulted in a decrease (by ~5%, P = 0.027) in V’O₂ during prior low-intensity exercise (20 W) and in shortening of τ_p of the V’O₂ on-kinetics (30.1±5.9 s vs. 25.4±1.5 s, P = 0.007) during subsequent heavy-intensity cycling. This was accompanied by a decrease of the slow component of V’O₂ on-kinetics by 49% (P = 0.001) and a decrease in the end-exercise V’O₂ by ~5% (P = 0.005). An increase (P = 0.02) in the vascular endothelial growth factor receptor 2 mRNA level and a tendency (P = 0.06) to higher capillary-to-fiber ratio in the vastus lateralis muscle were found after training (n = 11). No significant effect of training on the V’O_2peak was found (P = 0.12). However, the power output reached at the lactate threshold increased by 19% (P = 0.01). The power output obtained at the V’O_2peak increased by 14% (P = 0.003) and the time of 1,500-m performance decreased by 5% (P = 0.001). Computer modeling of the skeletal muscle bioenergetic system suggests that the training-induced decrease in the slow component of V’O₂ on-kinetics found in the present study is mainly caused by two factors: an intensification of the each-step activation (ESA) of oxidative phosphorylation (OXPHOS) complexes after training and decrease in the ‘‘additional” ATP usage rising gradually during heavy-intensity exercise.

In this study we examined the relationship between fast myosin heavy chain (MyHC2) content in the vastus lateralis and the rate of oxygen uptake (VO2) and heart rate (HR) increase during an incremental exercise in 38, young, healthy men. Prior to the exercise test, muscle biopsies were taken in order to evaluate the MyHC composition. It was found that during cycling performed below the lactate threshold (LT), a positive relationship between MyHC2 and the intercept of the oxygen uptake and power output (VO2-PO) relationship existed (r=0.49, P=0.002), despite no correlation between MyHC2 and the slope value of the VO2-PO relationship (r= -0.18, P=0.29). During cycling performed above the LT, MyHC2 correlated positively with the magnitude of the nonlinearity in the VO2-PO relationship; i.e. with the accumulated VO2'excess' (r=0.44, P=0.006) and peak VO2'excess' (r=0.44, P=0.006), as well as with the slope of the HR-PO relationship (r=0.49, P=0.002). We have concluded that a greater MyHC2 content in the vastus lateralis is accompanied by a higher oxygen cost of cycling during exercise performed below the LT. This seems to be related to the higher energy cost of the non-cross-bridge activities in the muscles possessing a greater proportion of MyHC2 content. In the case of heavy-intensity exercise, a higher MyHC2 content in the vastus lateralis is accompanied by greater non-linearity in the VO2-PO relationship, as well as a steeper increase in HR in the function of an increase of PO. This relationship can be explained by greater disturbances in metabolic stability in type II muscle fibres during exercise, resulting in a decrease of muscle mechanical efficiency and greater increase of heart rate at a given power output. Therefore, MyHC composition has an impact on the oxygen cost of cycling both below and above the LT.

New Findings: What is the central question of this study?A few weeks of endurance training accelerate the oxygen uptake () on‐kinetics in humans. The main aim of the present study was to determine whether the acceleration ofon‐kinetics obtained by a short period of moderate‐intensity training can be explained by an intensification of mitochondrial biogenesis. What is the main finding and its importance?We demonstrated that 5 weeks of moderate‐intensity training accelerates theon‐kinetics during moderate‐intensity cycling in the absence of enhanced mitochondrial biogenesis or capillarization in the trained muscles. We postulate that in the early stages of training an intensification of ‘parallel activation’ of oxidative phosphorylation could account for the shortening of theon‐transient. The effects of 5 weeks of moderate‐intensity endurance training on pulmonary oxygen uptake kinetics (on‐kinetics) were studied in 15 healthy men (mean ± SD: age 22.7 ± 1.8 years, body weight 76.4 ± 8.9 kg and maximal46.0 ± 3.7 ml kg⁻¹min⁻¹). Training caused a significant acceleration (P= 0.003) ofon‐kinetics during moderate‐intensity cycling (time constant of the ‘primary’ component 30.0 ± 6.6versus22.8 ± 5.6 s before and after training, respectively) and a significant decrease (P= 0.04) in the amplitude of the primary component (837 ± 351versus801 ± 330 ml min⁻¹). No changes in myosin heavy chain distribution, muscle fibre capillarization, level of peroxisome proliferator‐activated receptor γ coactivator 1α and other markers of mitochondrial biogenesis (mitochondrial DNA copy number, cytochromecand cytochrome oxidase subunit I contents) in the vastus lateralis were found after training. A significant downregulation in the content of the sarcoplasmic reticulum ATPase 2 (SERCA2;P= 0.03) and a tendency towards a decrease in SERCA1 (P= 0.055) was found after training. The decrease in SERCA1 was positively correlated (P= 0.05) with the training‐induced decrease in the gain of theon‐kinetics (at steady state/Δpower output). In the early stage of training, the acceleration inon‐kinetics during moderate‐intensity cycling can occur without enhanced mitochondrial biogenesis or changes in muscle myosin heavy chain distribution and in muscle fibre capillarization. The training‐induced decrease of the O₂cost of cycling could be caused by the downregulation of SERCA pumps.