Ca2+ and cross-bridge-induced changes in troponin C in skinned skeletal muscle fibers: effects of force inhibition.
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Changes in skeletal troponin C (sTnC) structure during thin filament activation by Ca2+ and strongly bound cross-bridge states were monitored by measuring the linear dichroism of the 5' isomer of iodoacetamidotetramethylrhodamine (5'IATR), attached to Cys98 (sTnC-5'ATR), in sTnC-5'ATR reconstituted single skinned fibers from rabbit psoas muscle. To isolate the effects of Ca2+ and cross-bridge binding on sTnC structure, maximum Ca2+-activated force was inhibited with 0.5 mM AlF4- or with 30 mM 2,3 butanedione-monoxime (BDM) during measurements of the Ca2+ dependence of force and dichroism. Dichroism was 0.08 +/- 0.01 (+/- SEM, n = 9) in relaxing solution (pCa 9.2) and decreased to 0.004 +/- 0.002 (+/- SEM, n = 9) at pCa 4.0. Force and dichroism had similar Ca2+ sensitivities. Force inhibition with BDM caused no change in the amplitude and Ca2+ sensitivity of dichroism. Similarly, inhibition of force at pCa 4.0 with 0.5 mM AlF4- decreased force to 0.04 +/- 0.01 of maximum (+/- SEM, n = 3), and dichroism was 0.04 +/- 0.03 (+/- SEM, n = 3) of the value at pCa 9.2 and unchanged relative to the corresponding normalized value at pCa 4.0 (0.11 +/- 0.05, +/- SEM; n = 3). Inhibition of force with AlF4- also had no effect when sTnC structure was monitored by labeling with either 5-dimethylamino-1-napthalenylsulfonylaziridine (DANZ) or 4-(N-(iodoacetoxy)ethyl-N-methyl)amino-7-nitrobenz-2-oxa-1,3-diazole (NBD). Increasing sarcomere length from 2.5 to 3.6 microm caused force (pCa 4.0) to decrease, but had no effect on dichroism. In contrast, rigor cross-bridge attachment caused dichroism at pCa 9.2 to decrease to 0.56 +/- 0.03 (+/- SEM, n = 5) of the value at pCa 9. 2, and force was 0.51 +/- 0.04 (+/- SEM, n = 6) of pCa 4.0 control. At pCa 4.0 in rigor, dichroism decreased further to 0.19 +/- 0.03 (+/- SEM, n = 6), slightly above the pCa 4.0 control level; force was 0.66 +/- 0.04 of pCa 4.0 control. These results indicate that cross-bridge binding in the rigor state alters sTnC structure, whereas cycling cross-bridges have little influence at either submaximum or maximum activating [Ca2+]. (+info)
The effect of thin filament activation on the attachment of weak binding cross-bridges: A two-dimensional x-ray diffraction study on single muscle fibers.
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To study possible structural changes in weak cross-bridge attachment to actin upon activation of the thin filament, two-dimensional (2D) x-ray diffraction patterns of skinned fibers from rabbit psoas muscle were recorded at low and high calcium concentration in the presence of saturating concentrations of MgATPgammaS, a nucleotide analog for weak binding states. We also studied 2D x-ray diffraction patterns recorded under relaxing conditions at an ionic strength above and below 50 mM, because it had been proposed from solution studies that reducing ionic strength below 50 mM also induces activation of the thin filament. For this project a novel preparation had to be established that allows recording of 2D x-ray diffraction patterns from single muscle fibers instead of natural fiber bundles. This was required to minimize substrate depletion or product accumulation within the fibers. When the calcium concentration was raised, the diffraction patterns recorded with MgATPgammaS revealed small changes in meridional reflections and layer line intensities that could be attributed in part to the effects of calcium binding to the thin filament (increase in I380, decrease in first actin layer line intensity, increase in I59) and in part to small structural changes of weakly attached cross-bridges (e.g., increase in I143 and I72). Calcium-induced small-scale structural rearrangements of cross-bridges weakly attached to actin in the presence of MgATPgammaS are consistent with our previous observation of reduced rate constants for attachment and detachment of cross-bridges with MgATPgammaS at high calcium. Yet, no evidence was found that weakly attached cross-bridges change their mode of attachment toward a stereospecific conformation when the actin filament is activated by adding calcium. Similarly, reducing ionic strength to less than 50 mM does not induce a transition from nonstereospecific to stereospecific attachment. (+info)
Pneumococcal psoas abscess.
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A 47-year-old woman was admitted to our hospital because of severe low back pain. A computed tomography (CT) scan revealed a left sided psoas muscle abscess. On the first hospital day, US-guided drainage was performed. Streptococcus pneumoniae was isolated from the pus. Thereafter, the open drainage of the abscess and antibiotic treatment were given with subsequent clinical improvement. Only 10 cases of pneumococcal psoas abscess have been previously reported in the world literature. (+info)
Antioxidative and oxidative status in muscles of pigs fed rapeseed oil, vitamin E, and copper.
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The susceptibility of a given muscle tissue to lipid oxidation may not only depend on the presence of unsaturated fatty acids and the balance between antioxidants and prooxidants, but also on the composition of the skeletal muscle. In the present study, the effects of dietary supplementation of vitamin E (dl-alpha-tocopheryl acetate) and copper in combination with a high level of monounsaturated fatty acids were examined with regard to the antioxidant concentration and the susceptibility to lipid oxidation of two muscles, longissimus (LD) and psoas major (PM), representing different oxidative capacity. In addition, fatty acid profiles of the backfat and the intramuscular lipids, as well as fresh meat quality traits, were studied. Pigs were allotted to a 3x3 factorial experiment with three levels of dl-alpha-tocopheryl acetate (0, 100, and 200 mg/kg of feed) and three levels of copper (0, 35, and 175 mg/kg of feed) added to a diet containing 6% rapeseed oil. A basal diet (without rapeseed oil) was added to the experimental design, giving a total of 10 dietary treatments. Muscle alpha-tocopherol concentrations increased (P<.001) with increasing dl-alpha-tocopheryl acetate in the feed. The antioxidative status was higher in PM than in LD, when considering the concentration of alpha-tocopherol (P<.001) and the activity of antioxidant enzymes (superoxide dismutase, P<.001; glutathione peroxidase, P = .06). Supplemental copper did not give rise to any deposition of copper in muscle tissue or backfat, but the antioxidant status of PM increased. The susceptibility to lipid oxidation was reduced in LD with increasing dietary dl-alpha-tocopheryl acetate and in PM with increasing dietary copper. Supplemental dl-alpha-tocopherol acetate improved the water-holding capacity of LD (P = .005) and PM (P = .003). The fatty acid composition of the backfat and the triglyceride fraction of the intramuscular fat became more unsaturated with the addition of rapeseed oil to the feed. Higher intakes of monounsaturated fatty acids due to the rapeseed oil were also reflected in the phospholipid fraction of the intramuscular fat, but no influence on the proportion of saturated fatty acids was seen. The susceptibility to lipid oxidation of PM was lower for pigs on the rapeseed oil-based diet than for those on the basal diet. The energy metabolic status of the muscles and the accumulation of calcium by the sarcoplasmic reticulum were not influenced by the dietary treatments, but there were differences between muscle types. The addition of rapeseed oil to the diet reduced the muscular content of glycogen (LD, P = .02; PM, P = .06) and elevated the plasma concentration of free fatty acids (P = .05). Overall, dietary fat, dl-alpha-tocopherol acetate, and copper affected the oxidative status of pig muscles, and the results differed depending on muscle type. (+info)
Anatomical differences in the psoas muscles in young black and white men.
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The anatomy of the psoas major muscle (PMA) in young black and white men was studied during routine autopsies. The forensic autopsies included 44 fresh male cadavers (21 black, 23 white) with an age span of 14 to 25 y. The range for weight was 66-76 kg and for height 169-182 cm. The PMA was initially measured in its entire length before measuring the diameter and circumference at each segmental level (L1-S1). At each segmental level, the calculated anatomical cross-sectional area (ACSA) was more than 3 times greater in the black group compared with the white (P < 0.001). The psoas minor muscle (PMI) was absent in 91% of the black subjects, but only in 13% of the white subjects. These data show that the PMA is markedly larger in black than white subjects. The marked race specific difference in the size of the PMA may have implications for hip flexor strength, spine function and race specific incidence in low back pathology, and warrants further investigation. (+info)
Effects of inorganic phosphate on endothermic force generation in muscle.
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Using a rapid (ca. 0.2 ms) laser temperature jump technique, the rate of endothermic force generation was examined in single-skinned (rabbit psoas) muscle fibres when they were exposed to different levels of inorganic phosphate (a product released during ATP hydrolysis in active muscle). The steady force is reduced by increased phosphate but the apparent rate constant of force generation induced by a standard temperature jump (from ca. 9 degrees C to ca. 12 degrees C) increases two- to threefold when the phosphate added is increased from zero to ca. 25 mM. The increase in the apparent rate constant also exhibits saturation at higher phosphate levels and the relation is hyperbolic. Detailed examination of the data, particularly in relation to our pressure release experiments, leads to a scheme for the molecular steps involved in phosphate release and force generation in active muscle fibres, where phosphate release from attached cross-bridges involves three reversible and sequentially faster molecular steps. Step one is a moderately slow, pre-force generation step that probably represents a transition of cross-bridges from non-specific to stereospecific attached states. Step two is moderately fast and represents endothermic cross-bridge force generation (temperature sensitive) and step three is a very rapid phosphate release. Such a scheme accommodates findings from a variety of different studies, including pressure perturbation experiments and other studies where the effect of phosphate on muscle force was studied. (+info)
Creatine kinase reaction in skinned rat psoas muscle fibers and their myofibrils.
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The aim of this study was to evaluate myofibrillar creatine kinase (EC 2.7.3.2) activity on the background of the effect of substrate channeling by myosin ATPase and to compare it with creatine kinase (CK) activity of whole skinned fibers. In order to assess CK activity, skinned fibers were prepared from the rat psoas major muscles defined by light microscopy. The activity in permeabilized fibers after treatment with saponin, Triton X-100 and Ca(2+)-free medium reached 2.80, 6.97 and 3.32 micromol ATP min(-1) mg(-1) protein, respectively, when a coupled enzyme assay system with external hexokinase and glucose-6-phosphate dehydrogenase was used. Transmission electron microscopy (TEM) revealed a possible interference among activities of sarcolemmal, sarcoplasmic, myofibrillar and mitochondrial CK from persisting structures. For evaluation of the myofibrillar CK itself, a pure myofibrillar fraction was prepared. Fraction purity was confirmed by TEM and by enzymatic assays for marker enzymes. Two procedures, i.e. the coupled enzyme assay and the evaluation of phosphocreatine (PCr) concentration before and after the CK reaction, were used for measurement of CK activity in this fraction. The procedures resulted in 3.2 nmol ATP min(-1) mg(-1) protein and 7.6 nmol PCr min(-1) mg(-1) protein, respectively. These alternative approaches revealed a discrepancy between the reacting portions of PCr by more than 50 %, which provides information about the size of the effect, generally described as substrate channeling. (+info)
Hip and ankle range of motion and hip muscle strength in young female ballet dancers and controls.
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OBJECTIVES: To compare the hip and ankle range of motion and hip muscle strength in 8-11 year old novice female ballet dancers and controls. METHODS: Subjects were 77 dancers and 49 controls (mean (SD) age 9.6 (0.8) and 9.6 (0.7) years respectively). Supine right active hip external rotation (ER) and internal rotation (IR) were measured using an inclinometer. A turnout protractor was used to assess standing active turnout range. The measure of ER achieved from below the hip during turnout (non-hip ER) was calculated by subtracting hip ER range from turnout range, and hip ER:IR was derived by dividing ER range by IR range. Range of right weight bearing ankle dorsiflexion was measured in a standing lunge using two methods: the distance from the foot to the wall (in centimetres) and the angle of the shank to the vertical via an inclinometer (in degrees). Right calf muscle range was measured in weight bearing using an inclinometer. A manual muscle tester was used to assess right isometric hip flexor, internal rotator, external rotator, abductor, and adductor strength. RESULTS: Dancers had less ER (p<0.05) and IR (p<0.01) range than controls but greater ER:IR (p<0.01). Although there was no difference in turnout between groups, the dancers had greater non-hip ER. Dancers had greater range of ankle dorsiflexion than controls, measured in both centimetres (p<0.01) and degrees (p<0.05), but similar calf muscle range. After controlling for body weight, controls had stronger hip muscles than dancers except for hip abductor strength which was similar. Regression analyses disclosed a moderate relation between turnout and hip ER (r = 0.40). There were no significant correlations between range of motion and training years and weekly training hours. CONCLUSIONS: Longitudinal follow up will assist in determining whether or not hip and ankle range in young dancers is genetically fixed and unable to be improved with further balletic training. (+info)