Muscle Myosin Heavy Chain Composition Research Articles

Improving human skeletal muscle myosin heavy chain fiber typing efficiency.

Single muscle fiber sodium dodecyl sulfate polyacrylamide gel-electrophoresis (SDS-PAGE) is a sensitive technique for determining skeletal muscle myosin heavy chain (MHC) composition of human biopsy samples. However, the number of fibers suitable to represent fiber type distribution via this method is undefined. Muscle biopsies were obtained from the vastus lateralis (VL) of nine resistance-trained males (25±1year, height=179±5cm, mass=82±8kg). Single fiber MHC composition was determined via SDS-PAGE. VL fiber type distribution [percent MHC I, I/IIa, IIa, IIa/IIx, and total "hybrids" (i.e. I/IIa+IIa/IIx)] was evaluated according to number of fibers analyzed per person (25 vs. 125). VL fiber type distribution did not differ according to number of fibers analyzed (P>0.05). VL biopsy fiber type distribution of nine subjects is represented by analyzing 25 fibers per person. These data may help minimize cost, personnel-time, and materials associated with this technique, thereby improving fiber typing efficiency in humans.

PC-FACS

PC-FACS

Power Output and Muscle Myosin Heavy Chain Composition in Young and Elderly Men

Aging is associated with a decline in muscle volume, power output, and the velocity at which peak power (Vopt) occurs. The current study aimed to examine the relationship between lower-limb power output characteristics, muscle myosin heavy chain (MHC) composition, and lean limb volume. Lower-limb power output during repeated efforts on an inertial sprint cycle and single-leg thrusts on the modified Nottingham power rig was studied in seven young and seven old males in relation to muscle MHC isoform composition of the vastus lateralis. Older subjects produced significantly lower power outputs and Vopt under all conditions (P < 0.01) and had lower proportions of fast MHC isoforms (P< 0.05). Peak power output during cycling was significantly related to lower-limb lean volume (r = 0.92, P < 0.05), whereas Vopt during sprint cycling was closely related to vastus lateralis MHC-II composition (r = 0.80, P < 0.05). These results provide further evidence of the importance of fast myosin isoform composition in the maintenance of dynamic muscle function in later life and particularly for maximal cycling performance.

Myosin heavy chain profiles and body composition are different in old versus young Standardbred mares

There are limited data on age-related changes in body composition or skeletal muscle in the horse. Therefore, the purpose of this study was to investigate any differences in muscle myosin heavy chain (MHC) and body composition associated with aging. Twenty-three young (4–8 years) and eight old (20+ years) unfit Standardbred mares were evaluated. Rump fat thickness was measured using B-mode ultrasound and per cent body fat (% fat) was calculated. Needle muscle biopsies were obtained from right gluteus medius muscle. MHC composition was determined via sodium dodecyl sulphate–polyacrylamide gel electrophoresis. Three MHC isoforms were subsequently identified as type I, type IIA, and type IIX and quantified using a scanning and densometric system. There were no significant differences ( p>0.05) between old and young mares in fat (%) (19.0±6.4 vs 20.5±5.4), fat mass (kg) (102.3±39.9 vs 106.9±37.1), or body weight (kg) (529.4±34.9 vs 512.7±57.7). However, the old mares had significantly ( p<0.05) greater lean body mass than the young mares (427.1±24.5 vs 405.7±37.9). Aged mares had significantly ( p<0.05) less type I (7.8±2.9% vs 12.1±4.4%) and IIA (27.8±7.1% vs 36.1±9.5%) fibres than the young group but more type IIX (64.6±4.7% vs 51.8±11.1%). The MHC data are consistent with the age-related changes seen in other species.

Aging does not attenuate plantaris muscle hypertrophy in male Fischer 344 rats.

The present study examined the effect of extreme old age on the plasticity of the rat plantaris muscle in response to an increase in mechanical load. Male Fischer 344 rats, aged 7 months (adult) and 25 months (old) underwent bilateral surgical ablation of the gastrocnemius muscle to functionally overload (OV) the fast-twitch plantaris muscle for 8 wk At 27 months of age, plantaris wet weight and cross-sectional area (CSA) were unaffected by age, but aging decreased peak isometric tension (Po) 27% (P < 0.05). Plantaris muscle myosin heavy chain composition indicated a loss of faster myosin heavy chains (MHC) isoforms with concomitant increases in slower MHC in old rats (P < 0.05). In adult rats, OV increased muscle CSA and Po 72% and 83%, respectively (P < 0.05). Similarly, OV increased CSA and Po 69% and 73%, respectively, in old rats (P < 0.05). Average fiber CSA increased 57% and 68% in adult-OV and old-OV rats, respectively (P < 0.05). Collectively, our data indicate that plantaris muscle mass and plasticity in response to increased mechanical load are well conserved in very aged male Fischer 344 rats.

A Molecular Mechanism for Variations in Muscle Function in Rainbow Trout

Salmonids undergo a developmental transition from parr to smolt that involves a number of physiological and morphological changes. In recent years, my laboratory has studied shifts in red muscle function at this parr-smolt transformation (PST) in rainbow trout, Oncorhynchus mykiss. Parr red muscle has faster contraction kinetics than smolts, including faster rates of activation and relaxation and a faster maximum shortening velocity. At PST, a transition in swimming behavior is also observed, with lower tailbeat frequencies and longer EMG duty cycles in the older smolts. Lastly, there is molecular correlate to changes in kinetics and behavior. During PST, there is a developmental reduction in the number of myosin heavy chain (MHC) isoforms in the red muscle of rainbow trout. Since MHC composition of muscle can determine contractile properties, these molecular results suggest a mechanism for the transition in red muscle kinetics and steady swimming. The red muscle of parr is more likely to contain the fast-twitch or white isoform of MHC, resulting in faster contractile properties of that muscle and higher tailbeat frequencies during steady swimming. Lastly, experimental work supports the conclusion that the shift in kinetics causes the observed shift in swimming behavior.

Growth hormone restores aged diaphragm myosin composition and performance after chronic undernutrition.

The effects of growth hormone (GH) on diaphragm muscle myosin heavy chain (MHC) composition and mechanical performance were investigated in Fischer 344 male rats aged to senescence (24.5 mo of age). Chronic undernutrition (UN), refeeding (RF), and RF+GH were compared with ad libitum feeding by using a model of UN that produced a 50% decrease in body weight over a 12-mo period. The effect of aging was assessed by comparing MHC composition of ad libitum-fed rats at 12 and 24.5 mo of age. At senescence, significant decreases in slow type I (-23%) and fast type IIA (-31%) MHC had occurred with aging. Conversely, UN over this aging period increased types I (32-73%) and IIA (22-23%) MHC and decreased fast types IIB (32-54%) and IIX (30-31%) MHC. RF and RF+GH reversed these shifts back toward control values. At senescence, maximal specific force, maximal velocity, and specific power capacity were not different across treatment groups. During repetitive isotonic contraction trials, the diaphragms of UN rats maintained power production over time (54% of initial power at 60 s), whereas the power production of diaphragms of ad libitum-fed rats fell to 0% (P < 0.05). In comparison with UN rats, the diaphragms of RF and RF+GH rats produced 23 (not significant) and 11% (P < 0.05) of initial power, respectively, suggesting that RF+GH treatment restored performance characteristics after UN. We conclude that RF+GH can reverse alterations in MHC composition and mechanical performance produced by chronic UN in the aged rat diaphragm.

Diaphragm myosin heavy chain composition shifts in aging chronically-undernourished Fischer 344 male rats.

The effects of chronic undernutrition (UN) on respiratory muscle were investigated during UN producing a 50% decrease in body weight over a prolonged period (45 weeks) in Fischer 344 male rats. This model focused on progressive, aging-related changes in myosin heavy chain (MHC) profile over time, in which the confounding effects of early development and late senescence were avoided. With aging toward late adulthood (68 weeks), MHC composition of control diaphragms was shifted, with decreased type I (slow) and IIA MHC, and increased type IIB and IIX (fast) MHC. UN produced a divergence of this profile, with an increase in type I and IIA MHC, and decreased type IIX MHC. UN diaphragms in vitro were more resistant to loss of active force with fatigue, during repetitive contractions. However, passive tension rose disproportionately during fatigue, suggesting increased fatigability. We conclude that the observed changes in diaphragm mechanical function are consistent with the UN-induced shifts in MHC composition; however, the elevated passive tension with fatigue suggests additional UN-induced changes in mechanical properties that are possibly detrimental to respiratory muscle function. The UN-dependent divergence in phenotype and mechanical properties may be amplified by aging-related shifts in muscle MHC composition over time, in the control group.

Skeletal muscle myosin heavy chain composition and resistance training.

We recently reported that 19 wk of heavy resistance training caused a decrease in the percentage of type IIb and an increase in the percentage of type IIa fibers as determined by qualitative histochemical analyses of myofibrillar adenosinetriphosphatase activity of biopsies of musculus vastus lateralis (Hather et al. Acta Physiol. Scand. 143: 177-185, 1991). These data were interpreted to suggest that resistance training had caused transformation among the fast-twitch fiber subtypes. To more clearly establish the influence of resistance training on muscle fiber composition, biopsies from the original study were analyzed biochemically for myosin heavy chain (MHC) composition by use of sodium dodecyl sulfate-polyacrylamide gel electrophoresis and histochemically for fiber types by use of myofibrillar adenosinetriphosphatase activity. The results show that after training (n = 13), IIb MHC composition decreased (P < 0.05) from 19 +/- 4 to 7 +/- 1%. IIa MHC, in contrast, increased (P < 0.05) from 48 +/- 3 to 60 +/- 2%. These responses were essentially mirrored by alterations in fiber type distribution. The percentage of type IIb fibers decreased (P < 0.05) from 18 +/- 3 to 1 +/- 1%, whereas the percentage of type IIa fibers increased from 46 +/- 4 to 60 +/- 3% (P < 0.05). Neither I MHC composition nor type I fiber percentage changed with training. The control group (n = 4) showed no changes in MHC composition or fiber type distribution. These results suggest that heavy resistance training alters MHC composition in human skeletal muscle, presumably reflecting a change in genetic expression.