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.

Background— Although we know much about the molecular makeup of the sinus node (SN) in small mammals, little is known about it in humans. The aims of the present study were to investigate the expression of ion channels in the human SN and to use the data to predict electrical activity. Methods and Results— Quantitative polymerase chain reaction, in situ hybridization, and immunofluorescence were used to analyze 6 human tissue samples. Messenger RNA (mRNA) for 120 ion channels (and some related proteins) was measured in the SN, a novel paranodal area, and the right atrium (RA). The results showed, for example, that in the SN compared with the RA, there was a lower expression of Na v 1.5, K v 4.3, K v 1.5, ERG, K ir 2.1, K ir 6.2, RyR2, SERCA2a, Cx40, and Cx43 mRNAs but a higher expression of Ca v 1.3, Ca v 3.1, HCN1, and HCN4 mRNAs. The expression pattern of many ion channels in the paranodal area was intermediate between that of the SN and RA; however, compared with the SN and RA, the paranodal area showed greater expression of K v 4.2, K ir 6.1, TASK1, SK2, and MiRP2. Expression of ion channel proteins was in agreement with expression of the corresponding mRNAs. The levels of mRNA in the SN, as a percentage of those in the RA, were used to estimate conductances of key ionic currents as a percentage of those in a mathematical model of human atrial action potential. The resulting SN model successfully produced pacemaking. Conclusions— Ion channels show a complex and heterogeneous pattern of expression in the SN, paranodal area, and RA in humans, and the expression pattern is appropriate to explain pacemaking.

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.

In classic concentric/eccentric exercise, the same absolute load is applied in concentric and eccentric actions, which infers a smaller relative eccentric load. We compared the effects of 6 weeks of classic concentric/eccentric quadriceps strength training (CON/ECC, 11 subjects) to eccentric overload training (CON/ECC+, 14 subjects) in athletes accustomed to regular strength training. The parameters determined included functional tests, quadriceps and fibre cross-sectional area (CSA), fibre type distribution by ATPase staining, localisation of myosin heavy chain (MHC) isoform mRNAs by situ hybridization and the steady-state levels of 48 marker mRNAs (RT-PCR) in vastus lateralis biopsies taken before and after training. Both training forms had anabolic effects with significant increases in quadriceps CSA, maximal strength, ribosomal RNA content and the levels of mRNAs involved in growth and regeneration. Only the CON/ECC+ training led to significantly increased height in a squat jump test. This was accompanied by significant increases in IIX fibre CSA, in the percentage of type IIA fibres expressing MHC IIx mRNA, in the level of mRNAs preferentially expressed in fast, glycolytic fibres, and in post-exercise capillary lactate. The enhanced eccentric load apparently led to a subtly faster gene expression pattern and induced a shift towards a faster muscle phenotype plus associated adaptations that make a muscle better suited for fast, explosive movements.

Using commercially available microarray technology, we investigated a series of transcriptional adaptations caused by atrophy of rat m. soleus due to 35 days of hindlimb suspension. We detected 395 out of 1,200 tested transcripts, which reflected 1%-5% of totally expressed genes. From various cellular functional pathways, we detected multiple genes that spanned a 200-fold range of gene expression levels. Statistical analysis combining L1 regression with the sign test based on the conservative Bonferroni correction identified 105 genes that underwent transcriptional adaptations with atrophy. Generally, expressional changes were discrete (<50%) and pointed in the same direction for genes belonging to the same cellular functional units. In particular, a distinct expressional adaptation of genes involved in fiber transformation; that is, metabolism, protein turnover, and cell regulation were noted and matched to corresponding transcriptional changes in nutrient trafficking. Expressional changes of extracellular proteases, and of genes involved in nerve-muscle interaction and excitation-contraction coupling identify previously not recognized adaptations that occur in atrophic m. soleus. Considerations related to technical and statistical aspects of the array approach for profiling the skeletal muscle genome and the impact of observed novel adaptations of the m. soleus transcriptome are put into perspective of the physiological adaptations occurring with muscular atrophy.