Myosin types in human skeletal muscle fibers

Favourable associations between the myosin heavy-chain and light-chain isoforms in human skeletal muscle

Histochemical and biochemical analyses were performed in order to examine the relationship between myosin light-chain (LC) isoforms and fibre-type distributions in whole human skeletal muscle. Muscle biopsies were obtained from the vastus lateralis muscle in six healthy men, and analysed for the relative area occupied by each fibre type (percentage of fibre type area) and the molar ratio of each LC isoform. The percentage of type I fibre area was positively correlated with the molar ratio of slow LC (LC1s and LC2s) to total LC. The regression line was located below the line of unity. Also, the ratio of percentage of type IIa fibre area to that of type II fibre area was positively correlated with the molar ratio of the fast alkali LC LC1f to fast alkali LCs LC1f and LC3f. These results support previous study, having shown that in human skeletal muscle some type I fibres express various amounts of fast LC in addition to slow LC and suggest that fast myosin heavy-chain HCIIa is favourably associated with LC1f, whereas HCIIb is favourably associated with LC3f.

Muscle fiber typing in routinely processed skeletal muscle with monoclonal antibodies

Muscle fiber typing is conventionally performed using mATPase enzyme histochemistry on cryostat sections. After pre-incubation of sections at pH 4.3, 4.6 and 10.3, based on the pattern of enzyme reactivity, the fibers can be classified in types I, II (subtypes A, AB and B) and the intermediate C (I and II) fibers. We have attempted to perform fiber typing of human psoas muscle by immunohistochemistry, using monoclonal antibodies R11D10 (specific for cardiac and type I skeletal myosin) and MY-32 (specific for fast muscle fibers) on cryostat as well as on paraffin sections. Staining of consecutive cryostat sections showed that type I fibers are R11D10 reactive whereas type II fibers are MY-32 reactive. Subtyping of type II fibers could not be performed by immunohistochemistry. Quantitative analysis of type I and II fibers showed that enzyme histochemical and immunohistochemical analysis are in close agreement.

Calcium and strontium activation characteristics of skeletal muscle fibres from the small marsupial Sminthopsis macroura

Mechanically skinned skeletal muscle fibres from the soleus and tibialis anterior muscles of the small marsupial Sminthopsis macroura were activated by Ca2+ and Sr2+ so that their isometric force properties could be determined. The properties characterized were the shape, slope and positions of the curves generated by plotting isometric force vs. pCa (-log10[Ca2+]) and pSr (-log10[Sr2+]), the maximum Ca2(+)-activated and Sr2(+)-activated tension (Ncm-2) and the frequency of force oscillations of myofibrillar origin during submaximal activations. The effect of caffeine on force activation was also studied. Apart from the fibres which exhibited physiological characteristics similar to those observed previously in mammalian fibres, a large proportion of fibres exhibited characteristics or combinations of characteristics which have not previously been described from healthy adult mammals. The results from 32 soleus fibres showed that only 23 could be categorized as either typical fast-twitch or slow-twitch fibres. The rest possessed unusual physiological characteristics which suggested the co-existence in the same fibre of Ca2(+)-regulatory and contractile properties from different categories of fast-twitch and slow-twitch fibres. We could distinguish two major fast twitch populations of tibialis anterior fibres which occurred in similar proportions. There were significant differences in the maximum tension produced by some of these groups of fibres. The tibialis anterior population fibres produced the highest maximum tension (ToCa 44.6 +/- 4.6 Ncm-2, n = 7) while the soleus combined type fibres produced the lowest maximum tension (ToCa 18.1 +/- 2.1 Ncm-2, n = 8). Our physiological observations of the Ca2(+)-activation and Sr2(+)-activation properties of soleus fibres in this study provide new evidence that there can be combinations of characteristics in single fibres and a continuum of properties between fibre types in normal mammalian skeletal muscles. These animals can therefore be used as a source of fibres with a wide range of properties.

Mechanisms of synaptic competition

The process of neuromuscular synapse elimination has been studied in the fourth deep lumbrical (4DL) muscle of the rat, a preparation which offers technical advantages for some types of experimental work. Studies have been performed both during development and in adult denervated muscles undergoing reinnervation. Results indicate that synapse elimination is dependent upon competition between motoneurons. Cellular mechanisms underlying this competition have also been explored. Both neuromuscular activity and muscle fiber type recognition appear to play a role, but positional cues appear unimportant in this small muscle.

Physiological properties of skinned fibres from normal and dystrophic (Duchenne) human muscle activated by Ca2+ and Sr2+

1. Contractile activation properties of various types of normal and dystrophic (Duchenne muscular dystrophy, DMD) human muscle fibres were investigated using mechanically skinned fibres activated in Ca2(+)- and Sr2(+)-buffered solutions at room temperature (21-25 degrees C). 2. The majority of the normal human muscle fibres (18/22; 82%) could be classified according to the Ca2(+)- and Sr2(+)-activation characteristics in the same three major groups as other mammalian skeletal muscle fibres studied previously: slow-twitch (8/22; 36%), fast-twitch (3/22; 14%) and fast-twitch intermediate (7/22; 32%), which correspond to the three major histological fibre types I, II B and IIA respectively. 3. Of these three major groups only the slow-twitch (type I; 14/24; 58%) and the fast-twitch intermediate (type IIA; 3/24; 13%) fibres were found in the DMD muscle, indicating that fast-twitch fibres of type IIB were in very low proportion in DMD muscle. 4. The DMD muscle contained a new group of fibres (4/24; 17%) with different Ca2(+)- and Sr2(+)-activation characteristics from the three major histological types. This group of fibres is likely to be of embryonic type. 5. The maximum tension development ability of DMD fibres was less than 20% of that in normal fibres with the exception of some slow-twitch fibres which could produce near normal tension. 6. A significant proportion of normal (4/22; 18%) and DMD (3/24; 13%) fibres were found to have a mixture of Ca2(+)- and Sr2(+)-activation characteristics. This can be explained by co-existence of various myofibrillar protein isoforms in different proportions with regulatory functions in the same individual fibre. 7. The results demonstrate that DMD leads to marked diminution in the ability of most individual skeletal muscle fibres to develop tension, and causes changes in the overall fibre-type distribution in afflicted muscles.

Thyroidal status and myosin isoenzymic pattern in the skeletal dorsal muscle of urodelan amphibians--the perennibranchiate Proteus anguinus

In the perennibranchiate Proteus anguinus, larval myosin isoforms were shown to coexist for life with the adult isomyosins that appeared at the end of the larval stage. Analysis of the myofibrillar ATPase profile also revealed that a high percentage of immature fibers persisted in adults. A long-term treatment with large amounts of T3 had no effect on juvenile individuals. Applied to subadult animals it promoted a regression of larval myosin isoforms and a reduction in the percentage of immature fiber types. The regulative effect of T3 in the myosin isoenzymic transition may be delayed and depends on metabolic conditions, which suggests it is indirect.

Quantitative analysis of histochemical and immunohistochemical reactions in skeletal muscle fibres of Rana and Xenopus

Intensities of histochemical and immunohistochemical reactions in muscle fibres of Rana and Xenopus have been estimated microphotometrically, and the data from serial sections statically analysed. Quantitative validities of reactions and measurements have also been assessed against independent published evidence. It is concluded that NADH-tetrazolium reductase overestimates tonic-fibre aerobic capacities and the actomyosin ATPase reaction overestimates their contraction speeds. However, it appears that succinate dehydrogenase, despite being a near-equilibrium enzyme of particulate distribution, indicates the relative aerobic capacities of fibres with acceptable accuracy when lightly reacted. Capacities for aerobic and anaerobic metabolism are positively correlated over all types of fibre (r typically approximately 0.6 for 200 fibres), perhaps as an adaptation to environmental hypoxia. Multivariate clusters (indicating fibre types) have been sought, using Ward's method with optimizing procedures (iterative relocation and multivariate-normal modelling). Cluster analysis confirms the subjective identifications of two 'slow/tonic' types in Xenopus (labelled T5 and S4) but of only one (T5) in Rana. Division of the 'fast family' twitch fibres into three types (F1-F3) in both genera, with metabolic capacity related inversely to apparent shortening velocity, is highly supportable by objective criteria. However, statistically significant subdivisions also present themselves. Rana F2 and Xenopus F1 clusters can be bisected according to metabolic capacity; and Xenopus F2 fibres fall into three subtypes reflecting different isomyosin contents. In the different types of twitch fibre, ratios of myofibrillar ATP consumption rate to aerobic capacity increase up to 30-fold with contraction speed, but anaerobic/aerobic ratios do so only 5-fold.

Is the myosin type altered in the aging platysma?

The myosin light chains of platysma samples originating from 2 to 86 year old patients of the maxillo-facial surgery clinic were investigated. The platysma contained both fast and slow myosin. No change in the proportion of myosin type in relation to age was found. Female patients often displayed less fast myosin than male patients. Each time when the platysma muscle activity has been reduced a decrease in the amount of slow myosin light chains was observed. In the reported study, variations of the fast and slow myosin light chains resulted mainly from the platysma activity level, i.e. from the pathology requiring the surgery, rather than from the patients' age.

Fiber sizes and histochemical characteristics of the rectus abdominis muscle of the rabbit under conditions of pregnancy and mechanically induced stress

Histochemical properties and muscle fiber diameters of the rectus abdominis (RA) muscle of the female rabbit were compared with those of RA muscle of (1) pregnant females at term of pregnancy (30 days); (2) pregnant females in which the stretch on the abdominal wall natural to pregnancy was artificially prolonged with a 40-day period of intraabdominal appliance; (3) virgin females subjected to intraabdominal appliance for 30, 45, 60, and 70 days. The RA muscle of the control female rabbits is composed of 29.73% type I, 12.13% type IIA, 57.59% type IIB, and 0.54% type IIC fibers. The stimulation on RA muscle due to either normal pregnancy or implant in virgin females provoked changes in muscle fiber diameters only; with the normal pregnancy plus the subsequent period of mechanical stimulation, changes occurred not only in muscle fiber diameters, but there was also a significant increase in the percentage of type I fibers and a concomitant decrease of type IIA and IIB fibers. The fiber-type pattern in the RA muscle of male and female rabbit also was compared. The RA muscle of the male rabbit showed more type IIA and less type IIB fibers than found in that of the female. Type I fibers were larger in the female, but type IIA fibers were larger in the male. In addition, male rabbits also were subjected to 30, 45, 60, and 70 days of RA muscle stimulation by means of an intraabdominal appliance to ascertain if the influence of such stimulation upon the RA muscle differed between the two sexes. Some differences in the response of the male RA muscle were noted.

Fiber hypertrophy in rat extraocular muscle following lateral rectus resection

Compensatory hypertrophy of muscle fibers occurs when tension on a skeletal muscle is increased. We looked for this phenomenon in response to strabismus surgery by performing a large right lateral rectus resection in 16 rats. Muscle fiber diameters of all horizontal rectus muscles were measured at 2-week postoperative intervals. Significant fiber hypertrophy occurred in both the antagonist right medial rectus and the resected right lateral rectus within 4 weeks. Fiber diameter subsequently returned to baseline in both muscles. We postulate that fiber hypertrophy in this setting may be a compensatory response to increased elastic load.

Cordotomy-denervation interactions on contractile and myofibrillar properties of fast and slow muscles in the rat

Cordotomy-denervation interactions were studied on contractile and myofibrillar properties of slow (soleus) and fast (extensor digitorum longus) muscles of the rat. The spinal cord was transected midthoracically in neonatal (2-day-old) animals. Two months after birth, a unilateral transection of the sciatic nerve was carried out in both cordotomized and control animals. Five weeks after denervation, contractile properties were tested isometrically in vitro; myofibrillar properties were assessed by histochemical staining of the muscle fibers and by electrophoretic analysis of the myosin heavy chain composition. The following results were obtained: (i) In cordotomized animals the contraction time of the soleus was significantly shorter (-23.3% on average) than that in the control animals and this shortening was accompanied by a proportional slow-to-fast shift in myofibrillar properties. (ii) The extensor digitorum longus properties were not significantly different in the control and cordotomized animals. (iii) Denervation in control animals was followed by a marked increase of contraction and half-relaxation times in the extensor digitorum longus, whereas in the soleus only the half-relaxation time was significantly increased; myofibrillar properties in the soleus showed an appreciable slow-to-fast shift, whereas in the fast muscle the main change was an increase in type 2A fibers to the detriment of type 2B. (iv) In cordotomized animals, denervation caused the soleus contraction time to increase to control values, whereas myofibrillar properties shifted to an even faster pattern; in the extensor digitorum longus denervation caused the same changes seen in the control animals. The results showed that cordotomy at birth caused the soleus to develop as a faster muscle than in the control animals. The concurrent effects of cordotomy and denervation on the myofibrillar properties of the soleus suggest that the slow-to-fast change in these properties is a common consequence of the reduction in the level of motor activity. The opposite effects of the two experimental conditions in the soleus contraction time support the view that the contractile alterations that follow denervation mainly reflect alterations in the muscle activation process.

Developmental transitions of myosin isoforms and organisation of the lateral muscle in the teleost Dicentrarchus labrax (L.)

In Dicentrarchus labrax (the sea bass) the differentiation of lateral muscle fibres occurs at different stages and in different ways in the superficial (red), intermediate (pink) and deep (white) regions of the myotome. At hatching the myotomes are composed of presumptive white and red fibres, the latter forming a superficial monolayer present only near the transverse septum. At this stage, differences between the fibre types are mainly ultrastructural. From their different reactions with isoform-specific antibodies to mullet myosin, and the appearance of histochemical mATPase activity, it appears that in both red and white muscle fibres there is a transition in myosin composition from an early larval form (L1R and L1W respectively) to a late larval form (L2R and L2W) and then to the isoforms typical of adult red and white muscle. The transition from L1W to L2W in the deep muscle occurs very rapidly and early in larval life (between 10 and 28 days), whereas the equivalent transition in the superficial muscle (from L1R to L2R) is a gradual process beginning in fibres near the transverse septum and spreading hypo- and epi-axially as this layer grows around the deep muscle. The definitive adult forms (AR and AW), distinguishable by the appearance of characteristic histochemical myosin ATPase activity, are present in the superficial red muscle by 80 days, but later in the deep white muscle (by 20 months), respectively. Compared to the superficial red and deep white muscle, the intermediate (pink) muscle layer first appears relatively late (80 days), but then acquires the histo- and immunohistochemical profile characteristic of the adult form much more rapidly.(ABSTRACT TRUNCATED AT 250 WORDS)

Exercise training induces transitions of myosin isoform subunits within histochemically typed human muscle fibres

Fibre type composition based on histochemical myosin ATPase reaction was studied in cross sections of biopsies from the vastus lateralis muscle of men. In addition, protein composition as well as peptide patterns of isolated myosin heavy chains were examined in batches of individually classified fibres from the same biopsies. High intensity endurance training during 8 weeks induces significant decreases by 31-70% of the type IIB fibre population in 3 of 4 subjects (in one case no change was observed). These decreases were offset by corresponding increases in either type I or type IIA fibres with the type IIC fibres remaining always below 3%. A total of 13 professional cyclists with training periods over several years have a 20 times lower content of type IIB fibres than 4 sedentary controls and a concomitant high content of 80% of type I fibres. The content of type I and type IIB fibres of 8 sprinter athletes did almost not differ from that of controls. Thus the type IIB fibres respond most sensitively with a decrease to aerobic endurance training. Since both type IIA and IIB fibres were identical in protein composition containing the same fast variety of myosin light chains and heavy chains as well as troponin-I, their interconversion could not be seen at the molecular level. However, the slow variety of myosin light chains and of troponin-I started accumulating after 8 weeks of training in type IIA fibres. Furthermore, the myosin heavy chain isoform started shifting by producing new peptide patterns that resemble the digestion pattern of slow myosin heavy chains in fibres which still classified as type IIA. These changes on the molecular level in type IIA fibres mark the beginning of their transition over the intermediate and variable type IIC fibres, towards the slow type I fibre.

Muscle fibre type composition, motoneuron firing properties, axonal conduction velocity and refractory period for foot extensor motor units in dystrophia myotonica

Seven patients with dystrophia myotonica were investigated using neurophysiological combined with histochemical techniques to elucidate motor unit properties in foot extensor muscles, which are often involved in the early stages of this disorder. For the 25 extensor digitorum brevis motor units studied the axonal conduction velocity, the axonal refractory period and the voluntary firing properties were within normal limits. However, high threshold motor units were not observed and the mean value of the axonal conduction velocities was lower (p less than 0.02) for the dystrophia myotonica motor units when compared with corresponding data from healthy subjects. There were also signs of impaired impulse propagation in the terminal part of the motor unit. In muscle biopsy specimens from the anterior tibial muscle, fibre type composition and structure were demonstrated using enzyme histochemical techniques for adenosine-triphosphate and immunohistochemical techniques for identification of the types of myosin isoform present. The histochemical findings indicated a type I fibre dominance, which was most obvious in the more seriously affected muscles. Neonatal myosin was observed preferentially in small but also in some normal sized fibres. Furthermore, some ring fibres were present and these showed staining with antineonatal myosin in their superficial portion. This indicates that an abnormal regeneration is one cause of the myopathic appearance of the muscle fibres in dystrophia myotonica. These investigations show that there is a reduced proportion of type II motor units in foot extensor muscles involved in the myopathy in dystrophia myotonica although it cannot definitely be established whether this is due to a loss of high threshold type II motor units or type II to type I transformation.

Myosin polymorphism in single fibers of chronically stimulated rabbit fast-twitch muscle

Rabbit tibialis anterior (TA) muscles were indirectly stimulated (10 Hz, 24 h/d) for 30 d and 60 d and single fibers were analysed using a combined histochemical and biochemical technique (Staron and Pette 1986, 1987a, b). After 30 d of chronic stimulation there was a pronounced increase in the normally rare (0.5%) C fiber population (i.e., fibers containing slow- and fast-myosins in varying ratios). At this time, C fibers amounted to almost 60% of the total population. In the 60 d stimulated muscles, the major population (98%) consisted of an atypical type It fiber. This fiber type which was not detectable in normal TA muscle, differed histochemically and biochemically from type I fibers. It contained the slow-myosin light chains LC1s and LC2s, the heavy chain HCI, and, in addition, high concentrations of the fast-myosin alkali light chain LC1f and possibly traces of a heavy chain with an electrophoretic mobility comparable with that of the fast-myosin heavy chain HCIIa. These It fibers were occasionally observed in the unstimulated, contralateral TA muscles which also contained an increased population of C fibers (1.3-6.3%). Although the transformation even after 60 d of chronic stimulation was incomplete, these changes demonstrate the ability of muscle fibers to adapt in a specific manner to altered functional demands brought about by an altered stimulus pattern. In addition, the pronounced heterogeneity of the fiber population undergoing transformation indicates a nonuniform response to a uniform stimulus pattern.

The multiplicity of combinations of myosin light chains and heavy chains in histochemically typed single fibres. Rabbit soleus muscle

1. Six adult rabbit soleus muscles were analysed by isolating histochemically identified fibre pieces from freeze-dried serial cross-sections. 2. By the use of this method, four fibre types (I, IC, IIC and IIA) were identified and analysed micro-electrophoretically. 3. Type I fibres contained the slow myosin heavy chain HCI and the slow myosin light chains LC1s and LC2s. 4. Type IIA fibres contained the fast myosin HCIIa with the fast light chains and, in addition, either LC1s or both LC1s and LC2s. 5. The C fibres (IC and IIC) represented intermediate populations between types I and IIC (IC) and between IC and IIA (IIC). They contained varied ratios of HCI/HCIIa with both sets of fast and slow light chains. With regard to myosin composition and isoforms of other myofibrillar proteins (M- and C-proteins, alpha-tropomyosin, troponin I), IC fibres resembled type I and IIC fibres resembled type IIA. 6. The presence of various myosin light and heavy chains within a specific fibre suggests a multiplicity of isomyosins. Without consideration of LC1sa and LC1sb differences, at least 54 possible isomyosins can be derived: type I fibres contain one isomyosin, types IC and IIC 54 possible isomyosins, and type IIA up to 18.

The multiplicity of combinations of myosin light chains and heavy chains in histochemically typed single fibres. Rabbit tibialis anterior muscle

1. Combined histochemical and biochemical single-fibre analyses [Staron & Pette (1987) Biochem. J. 243, 687-693], were used to investigate the rabbit tibialis-anterior fibre population. 2. This muscle is composed of four histochemically defined fibre types (I, IIC, IIA and IIB). 3. Type I fibres contain slow myosin light chains LC1s and LC2 and the slow myosin heavy chain HCI, and types IIA and IIB contain the fast myosin light chains LC1f, LC2f and LC3f and the fast heavy chains HCIIa and HCIIb respectively. 4. A small fraction of fibres (IIAB), histochemically intermediate between types IIA and IIB, contain the fast light myosin chains but display a coexistence of HCIIa and HCIIb. 5. Similarly to the soleus muscle, C fibres in the tibialis anterior muscle contain both fast and slow myosin light chains and heavy chains. The IIC fibres show a predominance of the fast forms and the IC fibres (histochemically intermediate between types I and IIC) a predominance of the slow forms. 6. A total of 60 theoretical isomyosins can be derived from these findings on the distribution of fast and slow myosin light and heavy chains in the fibres of rabbit tibialis anterior muscle.

Patterns of troponin T expression in mammalian fast, slow and promiscuous muscle fibres

The distribution of troponin T (TnT) species in typed single muscle fibres was analysed using one- and two-dimensional polyacrylamide gel electrophoresis (PAGE) and a monoclonal antibody specific for fast TnT. Fibres taken from erector spinae (Es), plantaris (Plt), diaphragm (Dia) and soleus (Sol) muscles of adult rabbits were pretyped as fast-twitch-glycolytic (FG), fast-twitch-oxidative-glycolytic (FOG), slow-twitch-oxidative (SO) or promiscuous (P) using a combination of histochemical staining and PAGE. Although none of the four size classes of TnT was either muscle or fibre type specific, their pattern of expression differed in each muscle and between the fibre types. FG fibres expressed TnT1f or TnT2f as predominant species, depending on the muscle; TnT3f and TnT4f were minor components. In contrast, all size classes of TnT were expressed in varying proportions in FOG fibres from Es and Plt, while those from Dia resembled FG fibres, expressing TnT1f as their major species. P fibres from Es, Plt, and Sol exhibited a distinctive pattern of fast TnT expression, TnT3f being the predominant species. Dia differed from the other muscles as TnT1f was the dominant fast TnT species in its P fibres as it is in the Dia fast fibres. Quantitative analysis of one- and two-dimensional gels revealed that the P fibres could be divided into two classes, those that exhibited discoordinate expression of fast and slow TnTs, myosin light chains and myosin heavy chains and those in which their expression was coordinate. In addition low levels of TnT4f were detected in SO fibres and of slow TnT in fast fibres.

Monoclonal antibody that detects human type I muscle fibres in routinely fixed wax embedded sections

A murine monoclonal antibody, F7, which selectively shows type I fibres in human skeletal muscle is reported. The antibody reacts with frozen sections and with formalin fixed wax embedded material. It should prove useful in the retrospective and prospective study of muscle pathology.

Cross reactive identification of types 1 and 2C fibers in human skeletal muscles with monoclonal anti-neurofilament (200 kd) antibody

Types 1 and 2C fibers in human skeletal muscle were cross-reactively identified with monoclonal anti-bovine neurofilament (200 kd) antibody. Thirty seven biopsy samples including sixteen vastus lateralis muscles, twelve lumbar paravertebral muscles, six gluteus medius muscles, two flexor carpi ulnaris muscles, and one flexor pollicis longus muscle, were examined. Serial transverse sections were stained histochemically with myofibrillar ATPase (pH 10.4, 4.6, 4.3) and DPNH-tetrazolium reductase reactions, and immunochemically using the avidin-biotin-peroxidase complex with the primary antibodies of monoclonal anti-bovine neurofilament (200 kd, 160 kd, 70 kd) antibodies and anti-bovine glial filament acidic protein antibody. The immunochemical reaction with anti-NF (200 kd) antibody could distinguish two kinds of fibers; positive and negative in all of the specimens. No fiber was recognized with other antibodies. Myosin ATPase reactions in serial sections proved that the positively stained fibers with anti-NF (200 kd) antibody were types 1 and 2C fibers and negative fibers types 2A and 2B fibers. At present, it is not known what substance is responsible for the cross-reaction with the monoclonal anti-NF (200 kd) antibody in types 1 and 2C fibers, but this unique antibody would be valuable in two aspects: one concerns the problem of the evolution of fiber types, and the other the utility as another supplemental method to conventional myosin ATPase scheme.

Immunocytochemical analysis of myosin heavy chains in human fetal skeletal muscles

Quadriceps muscle samples from human fetuses (10 weeks of gestation to term) were studied using immunocytochemical methods with monoclonal antibodies against fetal, adult-slow and adult-fast B myosin heavy chains. The monoclonal antibodies were selected for their virtually exclusive specificity for a particular isomyosin and used to investigate the expression of different myosin heavy chains during fetal development of muscle fibres. Concomitant studies of the myofibrillary ATPase pattern of muscle fibres were carried out. A fetal-specific myosin was persistently expressed during fetal life but at a continuously decreasing rate. Adult-slow myosin was observed in a small pool of muscle fibres, histochemically undifferentiated, in fetuses of 14-16 weeks of gestation. However, adult isomyosins appeared intensively only in the late fetal period, progressively replacing fetal myosin. The genes coding for adult-slow myosin are expressed earlier that those coding for adult-fast myosin. Myosin heavy chains specific for the neonatal period were not demonstrated with the antibodies used in this study. The contribution, provided by the present study, to the knowledge of the sequence of events in the expression of myosin heavy chains during normal muscle development, may allow a better understanding of eventual myosin changes which may occur in genetic muscle disorders.

Type 1, 2A, and 2B myosin heavy chain electrophoretic analysis of rat muscle fibers

Mammalian skeletal muscles are mixture of three type of fibers: type 1, type 2A, and type 2B fibers. Immunological studies and proteolytic analysis of myosin heavy chains from the three type of fibers have demonstrated the presence of distinct myosin isoforms. By using typed single muscle fibers and improving an electrophoretic method we are able to resolve three distinct polypeptides which are demonstrate to correspond to type 1, 2A and 2B myosin heavy chain isoforms by using specific monoclonal antibodies. The analysis of single muscle fibers shows that different myosin heavy chain isoforms are frequently coexpressed in the same muscle fiber.

Promiscuous expression of myosin in myotonic dystrophy

The pathologic changes in myotonic dystrophy (DM) skeletal muscle biopsies have been analyzed at both the histochemical and molecular level. A histochemical stain for pretyping single fibers in conjunction with sodium dodecyl sulphate-polyacrylamide gel electrophoresis allowed biochemical differences to be pinpointed in specific histochemical fiber types. These biochemical differences can be related to histochemical changes in fiber type observed in cross-section of the DM biopsies. Such changes included specific fiber type atrophy, hypertrophy, and disproportion. The pathogenesis of DM appears to be characterized by a large increase in the number of promiscuous fibers, that is, those fibers that express both fast and slow myosins. This promiscuity, which is rare in control muscle (less than 2%), is also prevalent at high levels in some family members at risk for DM. The observed promiscuity, although probably not a primary effect of DM, appears to be linked to the histochemical changes in fiber type observed in the DM biopsies.

Effect of exercise on the motor unit

The motoneuron part of this review deals with the changes in recruitment and firing rates of the motor unit types upon changes from a physically inactive life to endurance or strength training. The muscle fibers react to prolonged exercise by adaptation to a higher level of performance. A matter of discussion is the prerequisites for a transformation between the basic muscle fiber types, slow twitch and fast twitch, during voluntary (transsynaptic) activity, which is demonstrated after artificial nerve stimulation. The review includes current knowledge of muscle fiber transformation as an adaptive response to increased usage either by electrical stimulation or by transsynaptic neuronal activity. The metabolic adaptation related to increased endurance is reviewed with special reference to effects on muscle fibers. The increase in strength as a result of high resistance training is mainly the result of increased muscle cross-section. Whether this is solely the result of an increase in size of individual fibers or an increased fiber number is a controversial matter.

Purification and characterization of myosins from human and rabbit skeletal muscles by using specific monoclonal antibodies

By using immunoaffinity column chromatography slow (I) and fast (IIA, IIB) myosins were isolated from human (vastus lateralis) and rabbit (tibialis anterior, psoas and conoidal bundle) skeletal muscles. The peptide pattern revealed that slow (I) and fast (IIA, IIB) myosin heavy chains are quite distinct, as are those from pure slow (conoidal bundle) and fast (psoas) rabbit skeletal muscles. Unlike Billeter et al. (1981) the authors observed that fast human myosins were always associated with a small amount of slow myosin light chains. The fast myosins (IIA, IIB) from rabbit tibialis anterior muscle did not appear very distinct and contained only fast myosin light chains. These myosins were different from the IIB myosin from the psoas muscle. Ten per cent of the fibres revealed histochemically as fast IIA also reacted with an anti-slow myosin antibody. The classical histochemical techniques appear inadequate to demonstrate the existing differences among fibre types, but the monoclonal antibodies hold promise.

Correlation between myofibrillar ATPase activity and myosin heavy chain composition in rabbit muscle fibers

Combined histochemical and biochemical analyses were performed on single fibers of rabbit soleus muscle. Histochemically, four fiber types (I, IC, IIC, IIA) were defined. Of these, types I and IIA were separate, histochemically homogeneous groups. A heterogeneous C fiber population exhibited a continuum of staining intensities between types I and IIA. Microelectrophoretic analyses of specific, histochemically defined fibers revealed that type I fibers contained exclusively HCI, whereas type IIA fibers contained only HCIIa. The C fibers were characterized by the coexistence of both heavy chains in varying ratios, type IC with a predominance of HCI and type IIC with a predominance of HCIIa. A direct correlation existed between the myosin heavy chain composition and the histochemical mATPase staining and was especially evident in the C fiber population with its variable HCI/HCIIa ratio. This correlation did not apply to the myosin light chain complement.

Comparative study of myosins present in the lateral muscle of some fish: species variations in myosin isoforms and their distribution in red, pink and white muscle

Myosin isoforms and their distribution in the various fibre types of the lateral muscle of eight teleost fish (representing a wide range of taxonomic groups and lifestyles) were investigated electrophoretically, histochemically and immunohistochemically. Polyclonal antisera were raised against slow (red muscle) and fast (white muscle) myosins of the mullet, and used to stain sections of lateral muscle. Antisera specific for fast and slow myosin heavy chains only (anti-FHC and anti-SHC respectively) and for whole fast and slow myosins (anti-F and anti-S respectively) were obtained, and their specificity was confirmed by immunoblotting against electrophoretically separated myofibrillar proteins. The ATPase activity of myosin isoforms was examined histochemically using methods to demonstrate their acid- and alkali-lability and their Ca-Mg dependent actomyosin ATPase. As expected, the predominant myosin (and fibre) type in the red muscle showed an alkali-labile ATPase activity, reacted with the anti-S and anti-SHC sera (but not anti-F or anti-FHC) and contained two 'slow' light chains, whereas the predominant myosin (and fibre) type in the white muscle showed an alkali-stable ATPase activity, reacted with anti-F and anti-FHC sera (but not anti-S or anti-SHC) and contained three 'fast' light chains. However, superimposed upon this basic pattern were a number of variations, many of them species-related. On analysis by two-dimensional gel electrophoresis fish myosin light chains LC1s, LC2s and LC2f migrated like the corresponding light chains of mammalian myosins, but fish LC1f consistently had a more acidic pI value than mammalian LC1f. Fish LC3f varied markedly in Mr in a species-related manner: in some fish (e.g. eel and mullet) the Mr value of LC3f was less than that for the other two light chains (as in mammalian myosin), whereas in others it was similar to that of LC2f (e.g. cat-fish) or even greater (e.g. goldfish). Species differences were also seen in the relative intensity of LC1f and LC3f spots given by the fish fast myosins. In most of the fish examined the red muscle layer showed some micro-heterogeneity, containing (in addition to the typical slow fibres) small numbers of fibres with a histo- and immunohistochemical profile typical of white muscle (fast) fibres. However, other immunohistochemically distinct minority fibres were found in the red muscle of the goldfish. Three types of pink muscle were distinguished: a mosaic of immunohistochemically typical red and white fibres (e.g. grey mullet).(ABSTRACT TRUNCATED AT 400 WORDS)

Molecular heterogeneity of histochemical fibre types: a comparison of fast fibres

The relationship between histochemical fibre type and contractile protein expression was analysed in three rabbit skeletal muscles, the erector spinae, the plantaris and the diaphragm. A procedure for staining fibre bundles was developed using the same histochemical methods as those for typing fibres in cross-section. This allowed pretyped fibres to be selected and their molecular composition to be analysed by gel electrophoresis. The balance of expression of the two predominant fast troponin species, TnT1f and TnT2f, and alpha and beta tropomyosin subunits were studied in type IIA and IIB fast fibres. Type IIA fibres exhibited a restricted pattern of thin filament expression, exhibited TnT1f and both tropomyosin subunits in all three muscles. The expression in type IIB fibres, however, ranges from predominantly TnT2f and the alpha tropomyosin subunit in the erector spinae to TnT1f with both alpha and beta subunits in the diaphragm. These results indicate that there is not a simple one-to-one relationship between the fast muscle fibre subtypes and the expression of different thin filament protein isoforms.

Influences of endurance training on the ultrastructural composition of the different muscle fiber types in humans

To investigate changes in the ultrastructure of the different muscle fiber types induced by endurance training ten sedentary subjects (five women and five men) were exercised on bicycle ergometers 5 times a week for 30 min. After 6 weeks of training there were significant changes in VO2max (+14%), in the percentage of type I (+12%) and type IIB fibers (-24%) as well as in the volume densities of mitochondria. The latter increased 35% in type I, 55% in type IIA and 35% in type IIB fibers. The relative increase in subsarcolemmal mitochondria was larger than in interfibrillar mitochondria in all fiber types. There was also a significant increase in the volume density of intracellular lipid in type II fibres. It is concluded that high intensity endurance training leads to an enhancement of the oxidative capacity in all muscle fiber types.

Myofibrillar-protein isoforms and sarcoplasmic-reticulum Ca2+-transport activity of single human muscle fibres

In this study the polymorphism of myofibrillar proteins and the Ca2+-uptake activity of sarcoplasmic reticulum were analysed in single fibres from human skeletal muscles. Two populations of histochemically identified type-I fibres were found differing in the number of light-chain isoforms of the constituent myosin, whereas the pattern of light chains of fast myosin of type-IIA and type-IIB fibres was indistinguishable. Regulatory proteins, troponin and tropomyosin, and other myofibrillar proteins, such as M- and C-proteins, showed specific isoforms in type-I and type-II fibres. Furthermore, tropomyosin presented different stoichiometries of the alpha- and beta-subunits between the two types of fibres. Sarcoplasmic-reticulum volume, as indicated by the maximum capacity for calcium oxalate accumulation, was almost identical in type-I and type-II fibres, whereas the rate of Ca2+ transport was twice as high in type-II as compared with type-I fibres. It is concluded that, in normal human muscle fibres, there is a tight segregation of fast and slow isoforms of myofibrillar proteins that is very well co-ordinated with the relaxing activity of the sarcoplasmic reticulum. These findings may thus represent a molecular correlation with the differences of the twitch-contraction time between fast and slow human motor units. This tight segregation is partially lost in the muscle fibres of elderly individuals.

Development of fiber types in human fetal muscle. An immunocytochemical study

Human fetal muscles have been studied using immunocytochemical methods with antibodies directed against different myosin isoforms. We show that fiber type differences can be detected as early as 15-16 weeks of gestation. At this time it would appear that both the heavy and light chains characteristic of slow myosin are found in some myotubes.

Muscle fibre type composition in distal myopathy (Welander). An analysis with enzyme- and immuno-histochemical, gel-electrophoretic and ultrastructural techniques

The myopathic muscle of distal myopathy (Welander's disease), the dominantly inherited neuromuscular disorder which occurs frequently in Sweden, has been characterized by electron microscopy, enzyme- and immuno-histochemistry (using antibodies against embryonic, neonatal, fast and slow myosin, and against the muscle-specific intermediate filament protein, desmin), and with gel electrophoretic techniques. Of special interest is the fact that the ultrastructural appearance of the fibres with regard to M- and Z-band structures does not fit the proposed classification criteria for ultrastructural fibre typing of normal human muscle. Furthermore, contrary to previous results, we conclusively demonstrate that the predominating fibres are of a slow-twitch type. Unexpectedly, we also observed that embryonic and neonatal myosin was expressed in some residual fibres. This emphasises the importance of supplementing stains to demonstrate activity of ATPase with myosin immuno-histochemistry in order to improve understanding of fibre type characteristics in myopathic muscles. The origin of the myopathic muscle fibres in distal myopathy could not be definitely determined, but it is suggested that neurogenic disturbances play an important part in the pathophysiology of Welander's disease.

The fibre type composition of the striated muscle of the oesophagus in ruminants and carnivores

The fibre type composition of the striated muscle layer of the oesophagus of the cow, sheep, donkey, dog and cat was examined with standard histochemical methods and immunohistochemical staining using type-specific antimyosin sera. The heavy chain and light chain composition of oesophageal myosin was also examined using electrophoretic peptide mapping and 2-dimensional gel electrophoresis respectively. In the ruminants and donkey the oesophagus was composed of fibre types I, IIA and IIC with immunohistochemical characteristics identical to those of the same fibre types found in control skeletal muscle. In the ruminants there was a gradient in the proportion of type I fibres from 1% (at the cervical end) to about 30% (at the caudal end). In the carnivores the oesophageal muscle was composed of a very small percentage of type I and IIC fibres, but the predominant type was very different histochemically and immunohistochemically from all the fibre types (I, IIA, IIB, IIC) present in the control muscles. This oesophageal fibre type ( IIoes ) had an acid- and alkaline-stable m-ATPase activity, a moderate histochemical Ca-Mg actomyosin ATPase activity, and reacted weakly with anti-IIA and anti-IIB myosin sera. Although the light chains of the IIoes myosin were the same as the light chains of a mixture of IIA and IIB myosins, their respective heavy chains gave different peptide maps. Greater differences were obtained between the heavy chains of IIoes and other striated muscle myosins. These observations lead us to conclude that this predominant fibre type of the carnivore oesophageal striated muscle is of the 'fast' type, and contains a distinct isoform of myosin similar but not identical to the other fast type myosins.

Quantitative histochemistry of three mouse hind-limb muscles: the relationship between calcium-stimulated myofibrillar ATPase and succinate dehydrogenase activities

A quantitative modification of Meijer 's calcium-lead capture method, for the demonstration of calcium-stimulated myofibrillar ATPase activity at physiological pH, is described. A range of myofibrillar ATPase activities has been found among fast muscle fibres in two mouse hind-limb muscles. The myofibrillar ATPase activity of fast muscle fibres is 1.5-3 times higher than the myofibrillar ATPase activity of slow muscle fibres. Myofibrillar ATPase activities and succinate dehydrogenase activities of individual muscle fibres have been determined in serial sections. Activities of the two enzymes are correlated positively in soleus (fast and slow fibres), and negatively in plantaris (almost all fast) and extensor digitorum longus muscle (all fast). However, this correlation is not significant among the oxidative fibres in the extensor digitorum longus. The fibres of the latter muscle cannot be classified satisfactorily into two sub-types.

Improved resolution with one-dimensional polyacrylamide gel electrophoresis: myofibrillar proteins from typed single fibers of human muscle

Standard procedures for one-dimensional discontinuous sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis and silver staining were modified to give more effective separation and an improved resolution of human skeletal muscle proteins. In this system, an electrophoresis buffer composed of 100 mM L-isoleucine, 25 mM Tris base, and 0.1% SDS was used. The separating gel consisted of 16% acrylamide with N,N'-methylenebisacrylamide as a crosslinker (1:23), 0.4% SDS, 1.5 M Tris-HCl, pH 8.8. By the present procedure, the slow and the fast forms of myosin light chains (LCs, LCf) and other contractile proteins from human muscle could be better separated. The silver stain is based on a combination of methods previously described. The modified method requires a small fragment of a single fiber to observe as few as 10 ng of myofibrillar muscle proteins. The described simplifications made it possible to assay and compare up to 40 single fibers in the same electrophoretic run. Improved separation of other proteins migrating at basic pH could be achieved by a similar approach.

Heterogeneous distribution of myosin in human masticatory muscle fibres as shown by immunocytochemistry

On the basis of enzymic properties, different fibre types can be distinguished in human skeletal muscle (type I fibres and type II fibres with subtypes) and there is a correlation between fibre types and the occurrence of slow and fast myosin. In human masticatory muscles, fibres with ATPase activity at pH 9.4, intermediate between that of type I (low activity) and type II (high activity), are frequent. On cryostat-sectioned material, highly specific antibodies against fast myosin, slow myosin and slow light chains were applied. The myosin composition of human masticatory muscles was very heterogeneous, in contrast to that in limb muscles, with various proportions of slow and fast myosins, heavy as well as light chains. Type I fibres contained slow myosin only and type II mainly fast myosin, ATPase IM and type IIC fibres contained a mixture of slow and fast myosins in variable amounts. The findings conform with physiological evidence of a continuum of contraction times for motor units in the human masticatory muscles and suggests that these muscles are highly adapted to the special and complicated functions of the stomatognathic system.

Increases in myofibrillar ATPase intermediate human skeletal muscle fibers in response to endurance training

The response of human muscle triceps brachii (TB) to training, which consisted of skiing with sledges 500 miles over a period of 36 days, has been investigated by means of histochemical fiber typing (myofibrillar ATPase, n = 7). Muscle biopsies were taken in the right TB during pretraining, and in the right as well as in the left TB after training. The percentage of type 2 fibers and intermediate fibers (type 2C and 1B) in the right TB decreased and increased, respectively, by 13%. The fiber type distribution in the left TB after training was very similar to that in the right TB after training. This concordance indicates that the change in fiber type distribution was a result of the training per se, and not related to any eventual effect of the biopsy-sampling.

The fibre-type composition of the first branchial arch muscles in Carnivora and Primates

A combination of standard histochemical techniques and immunohistochemical staining using myosin type-specific antisera was used to determine the fibre-type composition of the muscles of first branchial arch origin (that is, masseter, temporalis, pterygoideus medialis and lateralis, tensor veli palatini, tensor tympani, anterior digastricus and mylohyoideus) in a wide range of the Carnivora and the Primates. The rare IIM fibre type was found in the first branchial arch muscles of most of the species examined, but never in the limb muscles used as controls for this study. The jaw-closer muscles (masseter, temporalis and pterygoideus medialis) were found to contain IIM fibres in all the Carnivora except the lesser panda and in all the Primates except man. When present, the IIM fibres were usually the predominant fibre type, and the only other fibre types present were types I, II or IIC. The presence of IIM fibres in the jaw-closer muscles of most of the Carnivora and the Primates seems to be associated with an aggressive bite which is required for predation by the former and defence by the latter. In both groups of species there was the member which does not have an aggressive bite, the lesser panda and man, respectively, and these (like all other orders of mammals such as Lagomorpha, Rodentia, etc.) were found to have no IIM fibres in the jaw-closer muscles. The two muscles of the first branchial arch group which are derived from the ventral constrictor muscles of the (phylogenetically) original mandibular arch never contained IIM fibres, and were composed of type I and II fibres similar to those found in the control muscles of the limb. Tensor veli palatini and tensor tympani showed species-dependent variations in fibre-type composition and did not always reflect the composition of the jaw-closer muscles. Thus their common origin with the jaw-closers cannot be responsible for the occurrence of IIM fibres in tensor veli palatini and tensor tympani in some species. Furthermore, in tensor tympani but not in tensor veli palatini, the presence of IIM fibres was always accompanied by immunohistochemically slow-tonic fibres. Finally, the regard to the association of oxidative activity with the fibre type as defined by the myofibrillar ATPase method and by the isoform of myosin present, we suggest that in the first branchial arch muscles this is probably not directly comparable to the situation in the typical limb muscle.

A new myofibrillar protein characteristic of type I human skeletal muscle fibres

Analysis of a single human type I (slow-twitch) skeletal muscle fibres by two-dimensional gel electrophoresis shows that they contain a specific protein of subunit Mr 34 x 10(3) and pI 6.0, 6.1 and 6.2 (three spots) which is absent from type IIA and IIB muscle fibres. This type I protein is located in the I-band of isolated myofibrils as demonstrated by the indirect immunofluorescence using specific antisera against the denatured form of type I protein. Type I protein could only be extracted from myofibrils with high salt solutions (0.6-1 M KCl), conditions which also coextract actin and myosin, demonstrating its firm attachment. Rat and cat type I muscle fibres as well as the slow-tonic fibres from chicken anterior latissimus dorsi also contained a protein homologous to the human type I protein. The human type I protein was found to be different from the known regulatory and contractile muscle proteins by electrophoretic and immunological criteria, and may therefore be a new myofibrillar protein in type I muscle fibres.

An enzyme-linked immunosorbent assay for antistriational antibodies associated with myasthenia gravis and thymoma: comparison with indirect immunofluorescence

Autoantibodies to the striations of skeletal muscle (AStrA) detected by immunofluorescence are useful in the diagnosis of a thymoma associated with myasthenia gravis (MG). With the intention of developing a better method, an enzyme-linked immunosorbent assay (ELISA) has been evaluated in 147 MG patients and 200 healthy controls. An additional 107 patients with various autoimmune diseases and autoantibodies were also tested. With a crude actomyosin preparation, the ELISA gave similar results to immunofluorescence, viz. positives in 42% of MG patients, but in all with a histologically proven thymoma. Less than 1% of the healthy controls were positive but false positives were found in patients with liver disease and anti-smooth muscle antibodies. After treatment of rheumatoid arthritis with D-penicillamine the titre of AStrA may rise. The ELISA was shown to be sensitive and reproducible, but immunofluorescence is a more practical method of distinguishing between the different categories of anti-muscle antibodies. ELISA should prove particularly useful for quantitation and sequential monitoring.

Myosin light-chain expression during avian muscle development

Monoclonal antibodies to adult chicken myosin light chains were generated and used to quantitate the types of myosin light-chain (MLC) isoforms expressed during development of the pectoralis major (PM), anterior latissimus dorsi (ALD), and medial adductor (MA) muscles of the chicken. These are muscles which, in the adult, are composed predominantly of fast, slow, and a mixture of fiber types, respectively. Three distinct phases of MLC expression characterized the development of the PM and MA muscles. The first identifiable pase occurred during the period of 5-7 d of incubation in ovo. Extracts of muscles from the pectoral region (which included the presumptive PM muscle) contained only fast MLC isoforms. This period of exclusive fast light-chain synthesis was followed by a phase (8- 12 d of incubation in ovo) in which coexpression of both fast and slow MLC isoforms was apparent in both PM and MA muscles. During the period, the composition of both fast and slow MLC isoforms in the PM and MA muscles was identical. Beginning at day 12 in ovo, the ALD was also subjected to immunochemical analyses. The proportion of fast and slow MLCs in this muscle at day 12 was similar to that present in the other muscles studied. The third development phase of MLC expression began at approximately 12 d of incubation in ovo and encompassed the transition in MLC composition to the isoform patterns incubation in ovo and encompassed the transition in MLC composition to the isoform patterns typical of adult muscle. During this period, the relative proportion of slow MLC rose in both the MA and ALD and fell in the PM. By day 16, the third fast light chain, LC(3f), was apparent in extracts of both the PM and MA. These results show that there is a developmental progression in the expression of MLC in the two avian muscles studied from day 5 in ovo; first, only fast MLCs are accumulated, then both fast and slow MLC isoforms are expressed. Only during the latter third of development in ovo is the final MLC isoform pattern characteristic of a particular muscle type expressed.

Myofibrillar ATPase activity in human muscle fast-twitch subtypes

Under local anesthesia, a muscle biopsy was removed from an individual with a high percentage of type II subtypes. The muscle sample was assayed for myofibrillar ATPase activity using various acid preincubation pH values. Subtle differences were found to exist in the acid-lability of ATPase activity among the type II fibers. These observations suggest different ratios of IIA/IIB myosis and may reflect a gradual transformation between type IIA and IIB fibers.