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Biomedical subjects

R Billeter

Publications and source records attributed to R Billeter.

At least 19 recordsLinked to original sources
PubMed2006

Expression of Kir2.1 and Kir6.2 transgenes under the control of the alpha-MHC promoter in the sinoatrial and atrioventricular nodes in transgenic mice.

Kir2.1 and Kir6.2 are ion channel subunits partly responsible for the background inward rectifier and ATP-sensitive K(+) currents (I(K1) and I(KATP)) in the heart. Very little is known about how the distribution of ion channel subunits is controlled. In this study, we have investigated the expression (at protein and mRNA levels) of GFP-tagged Kir2.1 and Kir6.2 transgenes under the control of the alpha-MHC promoter in the sinoatrial node (SAN), atrioventricular node (AVN), His bundle and working myocardium of transgenic mice. After dissection, serial 10-microm cryosections were cut. Histological staining was carried out to identify tissues, confocal microscopy was carried out to map the distribution of the GFP-tagged ion channel subunits and in situ hybridization was carried out to map the distribution of corresponding mRNAs. We demonstrate heterologous expression of the ion channel subunits in the working myocardium, but not necessarily in the SAN, AVN or His bundle; the distribution of the subunits does not correspond to the expected distribution of alpha-MHC. Both protein and mRNA expression does, however, correspond to the expected distributions of native Kir6.2 and Kir2.1 in the SAN, AVN, His bundle and working myocardium. The data demonstrate novel transcriptional and/or post-transcriptional control of ion channel subunit expression and raise important questions about the control of regional expression of ion channels.

Animals↗
PubMed2006

Connexins in the sinoatrial and atrioventricular nodes.

The sinoatrial node (SAN) and the atrioventricular node (AVN) are specialized tissues in the heart: the SAN is specialized for pacemaking (it is the pacemaker of the heart), whereas the AVN is specialized for slow conduction of the action potential (to introduce a delay between atrial and ventricular activation during the cardiac cycle). These functions have special requirements regarding electrical coupling and, therefore, expression of connexin isoforms. Electrical coupling in the center of the SAN should be weak to protect it from the inhibitory electrotonic influence of the more hyperpolarized non-pacemaking atrial muscle surrounding the SAN. However, for the SAN to be able to drive the atrial muscle, electrical coupling should be strong in the periphery of the SAN. Consistent with this, in the center of the SAN there is no expression of Cx43 (the principal connexin of the working myocardium) and little expression of Cx40, but there is expression of Cx45 and Cx30.2, whereas in the periphery of the SAN Cx43 as well Cx45 is expressed. In the AVN, there is a similar pattern of expression of connexins as in the center of the SAN and this is likely to be in large part responsible for the slow conduction of the action potential.

Action Potentials↗
PubMed2005

Computer three-dimensional reconstruction of the sinoatrial node.

BACKGROUND: There is an effort to build an anatomically and biophysically detailed virtual heart, and, although there are models for the atria and ventricles, there is no model for the sinoatrial node (SAN). For the SAN to show pacemaking and drive atrial muscle, theoretically, there should be a gradient in electrical coupling from the center to the periphery of the SAN and an interdigitation of SAN and atrial cells at the periphery. Any model should include such features. METHODS AND RESULTS: Staining of rabbit SAN preparations for histology, middle neurofilament, atrial natriuretic peptide, and connexin (Cx) 43 revealed multiple cell types within and around the SAN (SAN and atrial cells, fibroblasts, and adipocytes). In contrast to atrial cells, all SAN cells expressed middle neurofilament (but not atrial natriuretic peptide) mRNA and protein. However, 2 distinct SAN cell types were observed: cells in the center (leading pacemaker site) were small, were organized in a mesh, and did not express Cx43. In contrast, cells in the periphery (exit pathway from the SAN) were large, were arranged predominantly in parallel, often expressed Cx43, and were mixed with atrial cells. An approximately 2.5-million-element array model of the SAN and surrounding atrium, incorporating all cell types, was constructed. CONCLUSIONS: For the first time, a 3D anatomically detailed mathematical model of the SAN has been constructed, and this shows the presence of a specialized interface between the SAN and atrial muscle.

Animals↗
PubMed2004

Regulatory gene expression in skeletal muscle of highly endurance-trained humans.

AIM AND BACKGROUND: Changes in regulatory and structural gene expression provide the molecular basis for the adaptation of human skeletal muscle to endurance exercise. HYPOTHESIS: The steady-state levels of multiple mRNAs mainly involved in regulatory functions differ between highly endurance-trained and untrained subjects in a muscle heavily recruited during the exercise. METHODS: Biopsies from musculus vastus lateralis of seven untrained (UT) subjects [maximal oxygen consumption (VO2max) = 39 mL kg-1 min-1] and seven trained (T) professional cyclists (VO2max = 72 mL kg-1 min-1) were analysed for the contents of 597 different mRNAs using commercially available cDNA arrays (Clontech no. 7740-1). Intra-individual expression profiles were compared by least-square linear regression analysis. Differences in gene expression between the two groups were tested for statistical significance using L1 regression analysis combined with the sign test on all permutations of scatter plots of log raw values from UT vs. T subjects. RESULTS: Transcripts for 144 of 597 genes were sufficiently abundant to be analysed quantitatively. The expression profiles of the T group had a better intragroup correlation (R2) than those of the UT group (0.78 vs. 0.65, P < 0.05). An intergroup (T vs. UT) correlation of expression profiles gave an R2 of 0.71. Statistical analysis at a false discovery rate of 5% identified differential expression of nine cell-regulatory genes between T and UT. The mRNA levels of eight genes, including two DNA repair enzymes, transcription factors, signal transducers, a glycolytic enzyme and a factor involved in steroid hormone metabolism were increased in T vs. UT. Conversely, the mRNA of the tumour suppressor APC was downregulated with endurance training. Selective reverse-transcriptase polymerase chain reaction experiments confirmed the signal estimates from the array analysis. CONCLUSIONS: The repetitive impact of the complex exercise stimuli in professional cyclists attenuated the interindividual differences in regulatory gene expression in skeletal muscle. Long-term nuclear reprogramming of regulatory gene expression seems to be characteristic of human musculus vastus lateralis in a highly endurance-trained steady state.

Bicycling↗
PubMed2004

Muscular adaptations to computer-guided strength training with eccentric overload.

AIMS: In order to investigate the muscular adaptations to a novel form of strength training, 18 male untrained subjects performed 4 weeks of low resistance-high repetition knee extension exercise. METHODS: Nine of them trained on a conventional weight resistance device (Leg curler, CON/ECC group), with loads equivalent to 30% of the concentric one-repetition maximum (1RM) for both the concentric and eccentric phase of movement. The other nine trained on a newly developed computer-driven device (CON/ECC-OVERLOAD group) with the concentric load equivalent to 30% of the concentric 1RM and the eccentric load equivalent to 30% of the eccentric 1RM. RESULTS: Training resulted in significantly (P < or = 0.05) increased peak torque and a tendency (P=0.092) to increased muscle cross-sectional area for the CON/ECC-OVERLOAD but not the CON/ECC group, while strength endurance capacity was significantly (P < or = 0.05) increased in the CON/ECC group only. RT-PCR revealed significantly increased myosin heavy chain (MHC) IIa and lactate dehydrogenase (LDH) A mRNAs, a tendency for increased MHC IIx mRNA (P = 0.056) and high correlations between the changes in MHC IIx and LDH A mRNAs (r=0.97, P=0.001) in the CON/ECC-OVERLOAD group. CONCLUSIONS: These results indicate a shift towards a more type II dominated gene expression pattern in the vasti laterales muscles of the CON/ECC-OVERLOAD group in response to training. We suggest that the increased eccentric load in the CON/ECC-OVERLOAD training leads to distinct adaptations towards a stronger, faster muscle.

Adaptation, Physiological↗
PubMed2003

Effects of low-resistance/high-repetition strength training in hypoxia on muscle structure and gene expression.

To test the hypothesis that severe hypoxia during low-resistance/high-repetition strength training promotes muscle hypertrophy, 19 untrained males were assigned randomly to 4 weeks of low-resistance/high-repetition knee extension exercise in either normoxia or in normobaric hypoxia ( FiO(2) 0.12) with recovery in normoxia. Before and after the training period, isokinetic strength tests were performed, muscle cross-sectional area (MCSA) measured (magnetic resonance imaging) and muscle biopsies taken. The significant increase in strength endurance capacity observed in both training groups was not matched by changes in MCSA, fibre type distribution or fibre cross-sectional area. RT-PCR revealed considerable inter-individual variations with no significant differences in the mRNA levels of hypoxia markers, glycolytic enzymes and myosin heavy chain isoforms. We found significant correlations, in the hypoxia group only, for those hypoxia marker and glycolytic enzyme mRNAs that have previously been linked to hypoxia-specific muscle adaptations. This is interpreted as a small, otherwise undetectable adaptation to the hypoxia training condition. In terms of strength parameters, there were, however, no indications that low-resistance/high-repetition training in severe hypoxia is superior to equivalent normoxic training.

Adenosine Triphosphatases↗
PubMed2003

[Structure and function of skeletal muscles].

This review describes the structural make-up of muscle cells in term of the organization of the main myo-proteins into sarcomeres. The activation of muscle contraction is discussed on the cellular level as well as an integrative problem of activation of motor units for motor task. In this context the discrimination of muscle fibers into slow and fast types plays a role in particular with regard to specific athletic qualities. The energy supply systems present themselves as a sequence of distinct processes, which are responsible for power output for seconds, (phosphocreatine), minutes (glycolysis) and minutes to hours (oxidative phosphorylation). The supply of oxygen is a limiting condition for continued muscle work as the body does not maintain sizeable stores of oxygen. By contrast substrates (both carbohydrates and lipids) are stored in myocytes as well as systemically and do therefore not represent immediate limits to exercise performance.

Energy Metabolism↗
PubMed2003

[Effect of hypoxia on muscular performance capacity: "living low--training high"].

Altitude training is very popular among endurance athletes. But athletes respond very different on acute altitude exposure and altitude training. There are individual differences in the decrement of maximal oxygen consumption making general advices on the effect of altitude training very difficult. During the last few years different altitude training regimes have been developed. Beside "living high--training low," the concept of "living low--training high" becomes more and more popular. By this regime, athletes train under simulated or natural hypoxic conditions, while recovery time is spent at sea-level. Several studies show that with "living low--training high" maximal oxygen consumption as well as aerobic and anaerobic endurance performance can be improved. Molecular analysis reveal that a transcription factor called Hypoxia-Inducible Factor 1 (HIF-1) acts as a master gene in the regulation of hypoxia-dependent gene expression. In human skeletal muscle "living low-training high" induces the expression of glycolytic enzymes, the angiogenic factor VEGF, myoglobin as well as the increase of capillarity and mitochondrial content in parallel to the induction of the HIF-1 system. In trained human skeletal muscle, these adaptations cause a shift of substrate selection to an increased oxidation of carbohydrates as well as to an improvement of the conditions for transport and utilization of oxygen. Depending on the kind of sports, "living low--training high" can be used to train these muscular adaptations and to increase exercise performance.

Acid-Base Equilibrium↗
PubMed2003

Fiber type characteristics and myosin light chain expression in a world champion shot putter.

Muscle biopsies from m. vastus lateralis of two world class shot putters (shot putter 1 and 2) and the untrained brother of shot putter 1 were analyzed for fiber type distribution with ATPase staining and in situ hybridization for the expression of alkali myosin light chain (MLC) isoforms. Shot putter 2 had a predominance of type II fibers (67 X) and distinct hypertrophy of type I as well as type II fibers (fiber areas of 5939 and 8531 microm2). In shot putter 1, type II fibers amounted to only 40%, due to their selective hypertrophy, however type II fibers (10265 microm2) accounted for 67 2% of the total cross-sectional area. The type I fibers in shot putter 1 were similar in size to his untrained brother (3430 vs 3790 microm2). After 3 years of active detraining, type II fibers of shot putter 1 had reduced in size to values closer to those of his brother (7746 and 6340 microm2). The large difference between type I and type II fiber size, even in the untrained state, in both shot putter 1 and his brother is not usually seen in humans and maybe a genetic characteristic. We suggest that the ability to selectively increase the relative area of his type II fibers in the 15 years of strength training was a key element in his success as a shot putter. The observed increase in the expression of fast myosin light chain mRNAs in both fiber types is indicative of further adjustment of the myofibrillar apparatus towards the generation of very high peak power.

Adult↗
PubMed2001

Fiber type dependent upregulation of human skeletal muscle UCP2 and UCP3 mRNA expression by high-fat diet.

OBJECTIVE: To test the hypothesis that consumption of a high-fat diet leads to an increase in UCP mRNA expression in human skeletal muscle. In a group of endurance athletes, with a range in fiber type distribution, we hypothesized that the effect of the high-fat diet on UCP2 and UCP3 mRNA expression is more pronounced in muscle fibers which are known to have a high capacity to shift from carbohydrate to fat oxidation (type IIA fibers). DESIGN: Ten healthy trained athletes (five males, five females) consumed a low-fat diet (17+/-0.9 en% of fat) and high-fat diet (41.4+/-1.4 en% fat) for 4 weeks, separated by a 4 week wash-out period. Muscle biopsies were collected at the end of both dietary periods. MEASUREMENTS: Using RT-PCR, levels of UCP2 and UCP3 mRNA expression were measured and the percentage of type I, IIA and IIB fibers were determined using the myofibrillar ATPase method in all subjects. RESULTS: UCP3L mRNA expression tended to be higher on the high-fat diet, an effect which reached significance when only males were considered (P=0.037). Furthermore, diet-induced change in mRNA expression of UCP3T (r: 0.66, P=0.037), UCP3L (r: 0.61, P=0.06) and UCP2 (r: 0.70, P=0.025), but not UCP3S, correlated significantly with percentage dietary fat on the high-fat diet. Plasma FFA levels were not different during the two diets. Finally, the percentage of type IIA fibers was positively correlated with the diet-induced change in mRNA expression for UCP2 (r: 0.7, P=0.03), UCP3L (r: 0.73, P=0.016) and UCP3T (r: 0.68, P=0.03) but not with UCP3S (r: 0.06, NS). CONCLUSION: UCP2 and UCP3 mRNAs are upregulated by a high-fat diet. This upregulation is more pronounced in humans with high proportions of type IIA fibers, suggesting a role for UCPs in lipid utilization.

Adult↗
PubMed2001

Training high--living low: changes of aerobic performance and muscle structure with training at simulated altitude.

This study was undertaken to test the hypothesis that endurance training in hypoxia is superior to training of the same intensity in normoxia. To avoid adaptation to hypoxia, the subjects lived under normoxic conditions when not training. A secondary objective of this study was to compare the effect of high- vs. moderate-intensity training on aerobic performance variables. Thirty-three men without prior endurance training underwent a cycle ergometer training of 6 weeks, 5 d/week, 30 minutes/d. The subjects were assigned to 4 groups, N-high, N-low, H-high and H-low based on the training criteria normoxia (N; corresponding to a training altitude of 600 m), vs. hypoxia (H; training altitude 3850 m) and intensity (high; corresponding to 80% and low: corresponding to 67% of VO2max). VO2max measured in normoxia increased between 8.5 to 11.1%, independent of training altitude or intensity. VO2max measured in hypoxia increased between 2.9 and 7.2%. Hypoxia training resulted in significantly larger increases than normoxia training. Maximal power that subjects could maintain over a thirty-minute period (measured in normoxia or hypoxia) increased from 12.3 - 26.8% independent of training altitude. However, subjects training at high intensity increased performance more than subjects training at a low intensity. Muscle volume of the knee-extensors as measured by magnetic resonance imaging increased significantly in the H-high group only (+ 5.0%). Mitochondrial volume density measured by EM-morphometry in biopsy samples of m. vastus lat. increased significantly in all groups with the highest increase seen in the H-high group (+ 59%). Capillary length density increased significantly in the H-high group only (+ 17.2%). The main finding of this study is that in previously untrained people, training in hypoxia while living at low altitude increases performance in normoxia to the same extent as training in normoxia, but leads to larger increases of aerobic performance variables when measured under hypoxic conditions. Training intensity had no effect on the gain of VO2max. On the level of skeletal muscle tissue, the combination of hypoxia with high training intensity constitutes the most effective stimulus for increasing muscle oxidative capacity.

Acclimatization↗
PubMed2001

Molecular adaptations in human skeletal muscle to endurance training under simulated hypoxic conditions.

This study was performed to explore changes in gene expression as a consequence of exercise training at two levels of intensity under normoxic and normobaric hypoxic conditions (corresponding to an altitude of 3,850 m). Four groups of human subjects trained five times a week for a total of 6 wk on a bicycle ergometer. Muscle biopsies were taken, and performance tests were carried out before and after the training period. Similar increases in maximal O(2) uptake (8.3-13.1%) and maximal power output (11.4-20.8%) were found in all groups. RT-PCR revealed elevated mRNA concentrations of the alpha-subunit of hypoxia-inducible factor 1 (HIF-1) after both high- (+82.4%) and low (+78.4%)-intensity training under hypoxic conditions. The mRNA of HIF-1alpha(736), a splice variant of HIF-1alpha newly detected in human skeletal muscle, was shown to be changed in a similar pattern as HIF-1alpha. Increased mRNA contents of myoglobin (+72.2%) and vascular endothelial growth factor (+52.4%) were evoked only after high-intensity training in hypoxia. Augmented mRNA levels of oxidative enzymes, phosphofructokinase, and heat shock protein 70 were found after high-intensity training under both hypoxic and normoxic conditions. Our findings suggest that HIF-1 is specifically involved in the regulation of muscle adaptations after hypoxia training. Fine-tuning of the training response is recognized at the molecular level, and with less sensitivity also at the structural level, but not at global functional responses like maximal O(2) uptake or maximal power output.

Acyl-CoA Dehydrogenase↗
PubMed1999

Muscle structure with low- and high-fat diets in well-trained male runners.

Endurance capacity, maximal oxygen uptake capacity (VO2max) and quantitative muscle ultrastructural composition was analyzed in 7 well-trained male runners (mean age 37.1 years, mean VO2max 60 ml/min/kg) after a one month period of a low-fat diet (dietary fat intake 18.4% and a similar period of a high-fat diet (dietary fat intake 40.6%). Between these two interventional periods a washout period of one month was interspersed in which the nutritional fat content was approx. 32%; close to the average American Diet. During all three periods protein content of the nutrition was kept nearly constant at 15%. After the high-fat diet time to exhaustion in the endurance test increased significantly by 21% while VO2max remained unchanged. Muscle mitochondrial volume density remained unchanged while the intramyocellular fat content increased by 60%. Due to large interindividual differences in this variable this difference did not become statistically significant. While some 20% of the mitochondria are located in a subsarcolemmal location, only 10% of the lipid stores are associated with these mitochondria. Less than 2% of the mitochondrial outer surface are in contact with lipid droplets whereas 25-35% of the lipid surface is in contact with mitochondria. None of these variables is significantly altered after a high-fat diet. It is concluded that the change in endurance capacity of the subjects cannot be explained based on the structural changes observed in skeletal muscle tissue. This may be related to methodological problems associated with the determination of intramyocellular fat content.

Adult↗
PubMed1998

Fibre-type specific expression of fast and slow essential myosin light chain mRNAs in trained human skeletal muscles.

The fibre-type specific expression patterns of fast and slow isoforms of essential (alkali) myosin light chains (ELC) was analysed in trained, untrained and pathological human muscles. Biopsies from m. vastus lateralis of moderately trained and untrained persons, as well as highly trained endurance and strength athletes were analysed, by in situ hybridization, for the expression of the 'fast' ELC 1f/3f and the 'slow' ELC 1 sb. We wanted to investigate if changes in the fibre-type specific ELC mRNA pattern could be used as markers for training adaptation, especially, if the mRNA of the slow ELC 1sb isoform would appear in type IIA fibres as a result of endurance training (Baumann et al. 1987). We found the fast/slow ELC expression patterns in the fibre types to be remarkably stable. Physiological stress, even high training loads, did not affect it. No IIA fibres expressing ELC 1sb mRNA were found. They could be detected, however, in pathological muscle samples, where fast/slow ELC patterns not found in normal muscles were frequent. Our data suggest that in healthy muscles, only a subset of the theoretically possible combinations of myosin heavy and light chain isoforms are expressed at the level of their mRNAs.

Adenosine Triphosphatases↗
PubMed1998

Expression of fos and jun genes in human skeletal muscle after exercise.

It is believed that the induction of the fos and jun gene family of transcription factors might be at the origin of genetic events leading to the differential regulation of muscle-specific genes. We have investigated the effect of a 30-min running bout in untrained subjects on the expression of the mRNAs of all members of the fos and jun gene families, including c-fos, fosB, fosBdel, fra-1, and fra-2 as well as c-jun, junB, and junD. While the fos family members were transiently upregulated 10- to 20-fold (an exception being fra-2) the induction of the jun family members was up to 3-fold only. The induction of c-fos could also be demonstrated at the protein level. Both c-fos and c-jun mRNAs were coinduced in muscle fiber nuclei. The induction was not restricted to a particular fiber type, as expected from established muscle fiber recruitment schemes, but followed a "patchy" pattern confined to certain regions of the muscle. The signals leading to the expression of these immediate early genes are therefore unclear.

Adult↗
PubMed1996

Hsp70 expression in human skeletal muscle after exercise.

Prolonged exercise of a sufficiently high intensity is thought to create physiological stress and to disturb cellular homeostasis, ultimately inducing cellular adaptations which enable the organism to better deal with any future exercise challenge. Heat shock proteins (hsp) are expressed when cells are exposed to different types of stress. In this study, we have investigated whether the expression of the heat inducible form of hsp70 is increased in human skeletal muscle cells after a single bout of exercise. Five untrained subjects performed an exercise bout at their individual anaerobic threshold for 30 min on a treadmill. Hsp70 mRNA concentration was significantly increased by a factor of four at 4 min post-exercise. Similarly high levels were also observed 30 min and 3 h after the end of exercise. Hsp70 protein concentration, on the contrary, did not change within 3 h after cessation of exercise. Thus, a single exercise bout in humans is able to increase the steady state concentration of hsp70 mRNA, but is probably not sufficient to have an effect on the already high basal level of its protein. The analysis of hsp70 mRNA is potentially useful as a method to detect stress in tissues with a high basal level of heat shock proteins.

Adult↗
PubMed1996

Fiber-type-specific expression of essential (alkali) myosin light chains in human skeletal muscles.

We studied the expression patterns of the essential (alkali) myosin light-chain isoforms in adult human skeletal muscles, using in situ hybridization and single-fiber protein analysis. In analogy to other species, we found that the fiber type-specific expression of essential myosin light chains is regulated via the availability of the respective mRNAs in a given fiber. In contrast to other species, the slow isoform 1sa was only expressed in the most oxidative Type I fibers (Subtype IA) in addition to 1sb. These fibers also contained high levels of carbonic anhydrase III. Within the fibers, the essential myosin light-chain mRNAs were located preferentially in the perinuclear regions and to a lesser extent in the intermyofibrillar spaces, a distribution that excludes cotranslational assembly of these light chains into the myofibrils as the main mechanism. In comparing leg and shoulder muscles, we found less distinct fiber typing in the expression patterns of the essential myosin light chains in the leg muscles than in muscles from the shoulder region.

Adult↗