August Krogh Institute

About: August Krogh Institute is a based out in . It is known for research contribution in the topics: Skeletal muscle & Na+/K+-ATPase. The organization has 235 authors who have published 322 publications receiving 18914 citations.

Activity profile of competition soccer.

Abstract: In order to study the movement pattern of soccer players, 14 top-level players were filmed during several competitive matches. In addition, the relationship between the observed activity during match play and blood lactate values was examined. The mean distance covered during competitive matches was 10.80 km, and the average individual difference between matches was 0.92 km, with no difference in regard to high intensity activities. Midfielders covered a 10% longer (p less than 0.05) distance (11.4 km) than defenders and forwards, with no difference concerning high intensity running. There was a significant correlation (r = 0.61, p less than 0.05) between the amount of high intensity running during the match and lactate concentration in the blood. The results suggest that high intensity running can be used for making comparisons in soccer and that the interpretation of blood lactate in soccer is limited to giving an indication of the type of activity that has been carried out a few minutes before sampling.

Fiber types and metabolic potentials of skeletal muscles in sedentary man and endurance runners

Abstract: This description of some of the present knowledge on skeletal muscle fibers, their metabolic potentials, and their interplay with the degree of physical activity has revealed that skeletal muscle of man has a very large capacity for adaptation. Moreover, this adaptability appears to be of utmost importance for the metabolic response as well as for performance. Although all this is true, it should not distract us from the fact that we are lacking the most important information. The questions that need to be answered are: What triggers the changes to take place? Which are the regulatory mechanisms?

Metabolic characteristics of fibre types in human skeletal muscle.

Abstract: Muscle biopsy samples were obtained from healthy subjects in order to evaluate quantitative differences in single fibres of substrate (glycogen and triglyceride) and ion concentrations (Na+ and K+) as well as enzyme activity levels (succinate-dehydrogenase, SDH; phosphofructokinase, PFK; 3-hydroxyacyl-CoA-dehydrogenase, HAD; myosin ATPase) between human skeletal muscle fibre types. After freeze drying of the muscle specimen fragments of single fibres were dissected out and stained for myofibrillar-ATPase with preincubations at pH's of 10.3, 4.6, 4.35. Type I ("red") and II A,B, and C ("white") fibres could then be identified. Glycogen content was the same in different fibres, whereas triglyceride content was highest in Type I fibres (2-3 X Type II). No significant differences were observed for Na+ and K+ between fibre types. The activity for the enzymes studied were quite different in the fibre types (SDH and HAD, Type I is approximately 1.5 X Type II; PFK Type I is approximately 0.5 X Type II, Myosin ATPase Type I is approxiamtely 0.4 X Type II). The subgroups of Type II fibres were distinguished by differences in both SDH and PFK activities (SDH, Type II C is greater than A is greater than B; PFK, Type II B is greater than A is approximately C). It is concluded that contractile and metabolic characteristics of human skeletal fibres are very similar to many other species. One difference, however, appears to be than no Type II fibres have an oxidative potential higher than Type I fibres.

Transcriptional activation of the IL-6 gene in human contracting skeletal muscle: influence of muscle glycogen content

Abstract: In humans, the plasma interleukin 6 (IL-6) concentration increases dramatically during low-intensity exercise. Measurements across the working limb indicate that skeletal muscle is the source of IL-6 production. To determine whether energy availability influences the regulation of IL-6 expression during prolonged exercise, six male subjects completed two trials consisting of 180 min of two-legged dynamic knee extensor with either normal or low (~60% of control) pre-exercise muscle glycogen levels. Increases in plasma IL-6 during exercise were significantly higher (P<0.05) in the low-glycogen (16-fold) trial verses the control (10-fold) trial. Transcriptional activation of the IL-6 gene in skeletal muscle was also higher in the low-glycogen trial; it increased by about 40-fold after 90 min of exercise and about 60-fold after 180 min of exercise. Muscle IL-6 mRNA followed a similar but delayed pattern, increasing by more than 100-fold in the low-glycogen trial and by about 30-fold in the control trial. These data demonstrate that exercise activates transcription of the IL-6 gene in working skeletal muscle, a response that is dramatically enhanced when glycogen levels are low. These findings also support the hypothesis that IL-6 may be produced by contracting myofibers when glycogen levels become critically low as a means of signaling the liver to increase glucose production.

Structure and mechanism of Na,K-ATPase: functional sites and their interactions

Abstract: The cell membrane Na,K-ATPase is a member of the P-type family of active cation transport proteins. Recently the molecular structure of the related sarcoplasmic reticulum Ca-ATPase in an E1 conformation has been determined at 2.6 A resolution. Furthermore, theoretical models of the Ca-ATPase in E2 conformations are available. As a result of these developments, these structural data have allowed construction of homology models that address the central questions of mechanism of active cation transport by all P-type cation pumps. This review relates recent evidence on functional sites of Na,K-ATPase for the substrate (ATP), the essential cofactor (Mg(2+) ions), and the transported cations (Na(+) and K(+)) to the molecular structure. The essential elements of the Ca-ATPase structure, including 10 transmembrane helices and well-defined N, P, and A cytoplasmic domains, are common to all PII-type pumps such as Na,K-ATPase and H,K-ATPases. However, for Na,K-ATPase and H,K-ATPase, which consist of both alpha- and beta-subunits, there may be some detailed differences in regions of subunit interactions. Mutagenesis, proteolytic cleavage, and transition metal-catalyzed oxidative cleavages are providing much evidence about residues involved in binding of Na(+), K(+), ATP, and Mg(2+) ions and changes accompanying E1-E2 or E1-P-E2-P conformational transitions. We discuss this evidence in relation to N, P, and A cytoplasmic domain interactions, and long-range interactions between the active site and the Na(+) and K(+) sites in the transmembrane segments, for the different steps of the catalytic cycle.