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IIb Fibres (iib + fibre)
Selected AbstractsThe Effect of Testosterone on Gastrocnemius Muscle Fibres in Growing and Adult Male and Female Rats: A Histochemical, Morphometric and Ultrastructural Study,ANATOMIA, HISTOLOGIA, EMBRYOLOGIA, Issue 2 2003. Üstünel Summary In this study, the effect of testosterone on gastrocnemius muscle fibres in growing and adult rats (male and female) was examined using histochemical, morphometric and ultrastructural techniques. After physiological saline (PS), olive oil (OvO) or olive oil + testosterone (OvOT) injections on 72 rats (growing and mature, 36 male and 36 female), the sample tissues of fibre types of the gastrocnemius muscle taken were examined by histochemical [alkaline adenosine triphosphatase (alk-ATPase), acid ATPase (ac-ATPase)], morphometric and ultrastructural techniques. In PS-injected control groups, the gastrocnemius muscle of both sexes contained all the fibre types studied [slow-oxidative muscle fibres (type I), fast-oxidative glycolytic muscle fibres (type IIA) and fast-glycolytic muscle fibres (type IIB)]. The type I fibres had the smallest diameter, type IIA had a medium diameter and type IIB fibres had the largest diameter. In OvO-injected groups, it was observed that the OvO had little effect on the gastrocnemius muscles of either sex, although there was significant enlargement of type IIB fibres. After the injection of OvOT, hypertrophy of muscle fibres was determined by morphometric study. The biggest increase in diameter was on type I fibres. In addition, degenerations on some mitochondria, accumulation of lipid droplets on type I and type II fibres, an increase in glycogen particles, bifurcation of myofibrils, an increase in the number and diameter of units resembling T tubules and an increase in ribosomal content were also observed in the same group by transmission electron microscope. Consequently, it was determined that testosterone can induce protein synthesis in gastrocnemius muscle fibres, and induces changes in shape and size, and also can change the appearance and the number of fibres. [source] Changes in skeletal muscle size, fibre-type composition and capillary supply after chronic venous occlusion in ratsACTA PHYSIOLOGICA, Issue 4 2008S. Kawada Abstract Aim:, We have previously shown that surgical occlusion of some veins from skeletal muscle results in muscle hypertrophy without mechanical overloading in the rat. The present study investigated the changes in muscle-fibre composition and capillary supply in hypertrophied muscles after venous occlusion in the rat hindlimb. Methods:, Sixteen male Wistar rats were randomly assigned into two groups: (i) sham operated (sham-operated group; n = 7); (ii) venous occluded for 2 weeks (2-week-occluded group; n = 9). At the end of the experimental period, specimens of the plantaris muscle were dissected from the hindlimbs and subjected to biochemical and histochemical analyses. Results:, Two weeks after the occlusion, both the wet weight of plantaris muscle relative to body weight and absolute muscle weight showed significant increases in the 2-week-occluded group (,15%) when compared with those in the sham-operated group. The concentrations of muscle glycogen and lactate were higher in the 2-week-occluded group, whereas staining intensity of muscle lipid droplets was lower in the 2-week-occluded group than those in the sham-operated group. The percentage of type I muscle fibre decreased, whereas that of type IIb fibre increased in the 2-week-occluded group when compared with the sham-operated group. Although the expression of vascular endothelial growth factor-188 mRNA increased, the number of capillaries around the muscle fibres tended to decrease (P = 0.07). Conclusion:, Chronic venous occlusion causes skeletal muscle hypertrophy with fibre-type transition towards faster types and changes in contents of muscle metabolites. [source] Differential Effects of Cold Exposure on Muscle Fibre Composition and Capillary Supply in Hibernator and Non-Hibernator RodentsEXPERIMENTAL PHYSIOLOGY, Issue 5 2001S. Egginton Changes in the composition of fibre types and the capillary supply of skeletal muscle (tibialis anterior) were quantified in rats and hamsters subjected to 8-10 weeks of cold exposure and reduced photoperiod (10 °C, 1 h light-23 h dark). Muscle mass decreased in both species (by 12% and 17%, respectively). Following acclimation to cold there were no specific changes in fibre cross-sectional area (FCSA) in rats, whereas in hamsters there was a substantial atrophy of Type II, but not Type I fibres. In rat muscle there was little difference between the two groups in average capillary to fibre ratio (C:F) (1.76 ± 0.15, normothermia, N; 1.69 ± 0.05, hypothermia, H) and average capillary density (CD) (188 ± 14 mm,2, N; 201 ± 12 mm -2, H). Similarly, the average C:F was unaltered in hamsters (2.75 ± 0.11, N; 2.72 ± 0.15, H), although the 30% smaller fibre size observed with hypothermia resulted in a corresponding increase in average CD, to 1539 ± 80 mm,2 (P < 0.01). However, there was a coordinated regional adaptation to cold exposure in hamsters resulting in capillary rarefaction in the glycolytic cortex and angiogenesis in the oxidative core. Following acclimation of rats to cold there was a reduction in the supply area of individual vessels (capillary domain), particularly in the cortex (9310, N; 8938 ,m2, H; P < 0.05). In contrast, hypothermic hamsters showed only a small decrease in mean domain area in the cortex (948 ,m2, N; 846 ,m2, H; n.s.) but a marked reduction in the core (871 ,m2, N; 604 ,m2, H; P < 0.01). Rats showed little or no change in local capillary supply (LCFR) to fast fibres on acclimation to cold, while in hamsters the LCFR of Type IIb fibres showed a decrease in the cortex (2.7, N; 2.3, H) and an increase in the core (3.0, N; 3.3, H) during acclimation to cold. These data suggest that during a simulated onset of winter rats maintain FCSA and capillary supply as part of an avoidance strategy, whereas hamsters increase muscle capillarity in part as a consequence of disuse atrophy. [source] Differences in sodium voltage-gated channel properties according to myosin heavy chain isoform expression in single muscle fibresTHE JOURNAL OF PHYSIOLOGY, Issue 21 2009F. Rannou The myosin heavy chain (MHC) isoform determines the characteristics and shortening velocity of muscle fibres. The functional properties of the muscle fibre are also conditioned by its membrane excitability through the electrophysiological properties of sodium voltage-gated channels. Macropatch-clamp is used to study sodium channels in fibres from peroneus longus (PL) and soleus (Sol) muscles (Wistar rats, n= 8). After patch-clamp recordings, single fibres are identified by SDS-PAGE electrophoresis according to their myosin heavy chain isoform (slow type I and the three fast types IIa, IIx, IIb). Characteristics of sodium currents are compared (Student's t test) between fibres exhibiting only one MHC isoform. Four MHC isoforms are identified in PL and only type I in Sol single fibres. In PL, maximal sodium current (Imax), maximal sodium conductance (gNa,max) and time constants of activation and inactivation (,m and ,h) increase according to the scheme I,IIa,IIx,IIb (P < 0.05). ,m values related to sodium channel type and/or function, are similar in Sol I and PL IIb fibres (P= 0.97) despite different contractile properties. The voltage dependence of activation (Va,1/2) shows a shift towards positive potentials from Sol type I to IIa, IIx and finally IIb fibres from PL (P < 0.05). These data are consistent with the earlier recruitment of slow fibres in a fast-mixed muscle like PL, while slow fibres of postural muscle such as soleus could be recruited in the same ways as IIb fibres in a fast muscle. [source] Ca2+ -activated myosin-ATPases, creatine and adenylate kinases regulate mitochondrial function according to myofibre type in rabbitTHE JOURNAL OF PHYSIOLOGY, Issue 3 2005N. Gueguen Mitochondrial respiration rates and their regulation by ADP, AMP and creatine, were studied at different free Ca2+ concentrations (0.1 versus 0.4 ,m) on permeabilized fibre bundles of rabbit skeletal muscles differing in their myosin heavy chain profiles. Four fibre bundle types were obtained: pure types I and IIx, and mixed types IIax (approximately 50% IIa and 50% IIx fibres) and IIb+ (60% IIb fibres, plus IIx and IIa). At rest, pure type I fibres displayed a much higher apparent Km for ADP (212 ,m) than IIx fibres (8 ,m). Within the IIax and IIb+ mixed fibre bundle types, two KADPm values were observed (70 ,m and 5 ,m). Comparison between pure IIx and mixed types indicates that the intermediate Km of 70 ,m most probably corresponds to the mitochondrial affinity for ADP in IIa fibres, the lowest Km for ADP (5 ,m) corresponding to IIx and IIb types. Activation of mitochondrial creatine and adenylate kinase reactions stimulated mitochondrial respiration only in type I and IIax fibre bundles, indicating an efficient coupling between both kinases and ADP rephosphorylation in type I and, likely, IIa fibres, since no effect was observed in pure IIx fibres. Following Ca2+ -induced activation of myosin-ATPase, an increase in mitochondrial sensitivity to ADP of 45% and 250% was observed in type IIax and I bundles, respectively, an effect mostly prevented by addition of vanadate, an inhibitor of myosin-ATPase. Ca2+ -induced activation of myosin-ATPase also prevented the stimulation of respiration rates by creatine and AMP in I and IIax bundles. In addition to differential regulation of mitochondrial respiration and energy transfer systems at rest in I and IIa versus IIx and IIb muscle fibres, our results indicate a regulation of phosphotransfer systems by Ca2+ via the stimulation of myosin-ATPases in type I and IIa fibres of rabbit muscles. [source] | ||||||||||