Ontogeny of the Pectoralis muscle in the little brown bat,Myotis lucifugus

The ontogeny of a primary flight muscle, the pectoralis, in the little brown bat (Myotis lucifugus: Vespertilionidae) was studied using histochemical, immunocytochemical, and electrophoretic techniques. In fetal and early neonatal (postnatal age 1–6 days) Myotis, histochemical techniques for myofibrillar ATPase (mATPase) and antibodies for slow and fast myosins demonstrated the presence of two fiber types, here called types I and IIa. These data correlated with multiple transitional myosin heavy chain isoforms and native myosin isoforms demonstrated with SDS-PAGE and 4% pyrophosphate PAGE. There was a decrease in the distribution and number of type I fibers with increasing postnatal age. At postnatal age 8–9 days, the adult phenotype was observed with regard to muscle fiber type (100% type IIa fibers) and myosin isoform profile (single adult MHC and native myosin isoforms). This “adult” fiber type profile and myosin isoform composition preceeded adult function by about 2 weeks. For example, little brown bats were incapable of sustained flight until approximately postnatal day 24, and myofiber size did not achieve adult size until approximately postnatal day 25. Although Myotis pectoralis is unique in being composed of 100% type IIa fibers, transitional fiber types and isoforms were present. These transitional forms had been observed previously in other mammals bearing mixed adult muscle fibers and which undergo transitional stages in muscle ontogeny. However, in Myotis pectoralis, this transition transpires relatively early in development. © 1994 Wiley-Liss, Inc.     

Histochemical and myosin composition of vampire bat (Desmodus rotundus) pectoralis muscle targets a unique locomotory niche

The vampire bat pectoralis muscle contains at least four fiber types distributed in a nonhomogeneous pattern. One of these fiber types, here termed IIe, can be elucidated only by adenosine triphosphatase (ATPase) histochemistry combined with reactions against antifast and antislow myosin antibodies. The histochemical and immunohistochemical observations indicate a well-developed specialization of function within specific regions of the muscle. In parallel, analyses of native myosin isoforms and myosin heavy chain isoforms indicate two points. First, the histochemical “type IIe” fiber is predominant in cranial portions of the muscle, and myosin extracted from these regions exhibits a unique electrophoretic mobility not observed in the myosin isoforms of more traditional laboratory mammals. Second, the type I fibers are confined to the pectoralis abdominalis muscle and a small adjacent region of the caudal part of the pectoralis. This pattern of type I fiber distribution is considered a derived character state compared to muscle histochemical phenotype and isoform composition in the pectoralis muscles of other phyllostomids we have studied (Artibeus jamaicensis, Artibeus lituratus, Carollia perspicillata). We relate this to the unique locomotory needs of the common vampire bat, Desmodus rotundus. © 1993 Wiley-Liss, Inc.     

Alternative exon-encoded regions of Drosophila myosin heavy chain modulate ATPase rates and actin sliding velocity

To investigate the molecular functions of the regions encoded by alternative exons from the single Drosophila myosin heavy chain gene, we made the first kinetic measurements of two muscle myosin isoforms that differ in all alternative regions. Myosin was purified from the indirect flight muscles of wild-type and transgenic flies expressing a major embryonic isoform. The in vitro actin sliding velocity on the flight muscle isoform (6.4 microm x s(-1) at 22 degrees C) is among the fastest reported for a type II myosin and was 9-fold faster than with the embryonic isoform. With smooth muscle tropomyosin bound to actin, the actin sliding velocity on the embryonic isoform increased 6-fold, whereas that on the flight muscle myosin slightly decreased. No difference in the step sizes of Drosophila and rabbit skeletal myosins were found using optical tweezers, suggesting that the slower in vitro velocity with the embryonic isoform is due to altered kinetics. Basal ATPase rates for flight muscle myosin are higher than those of embryonic and rabbit myosin. These differences explain why the embryonic myosin cannot functionally substitute in vivo for the native flight muscle isoform, and demonstrate that one or more of the five myosin heavy chain alternative exons must influence Drosophila myosin kinetics.     

Myosin heavy chain expression during development and following denervation of fast fibers in the red strip of the chicken pectoralis

The myosin heavy chain composition of muscle fibers that comprise the red strip of the pectoralis major was determined at different stages of development and following adult denervation. Using a library of characterized monoclonal antibodies we found that slow fibers of the red strip do not react with antibodies to any of the fast myosin heavy chains of the superficial pectoralis. Immunocytochemical analysis of the fast fibers of the adult red strip revealed that they contain the embryonic fast myosin heavy chain rather than the adult pectoral isoform found throughout the adult white pectoralis. This was confirmed using immunoblot analysis of myosin heavy chain peptide maps. We show that during development of the red strip both neonatal and adult myosin heavy chains appear transiently, but then disappear during maturation. Furthermore, while the fibers of the superficial pectoralis reexpress the neonatal isoform as a result of denervation, the fibers of the red strip reexpress the adult isoform. Our data demonstrate a new developmental program of fast myosin heavy chain expression in the chicken and suggest that the heterogeneity of myosin heavy chain expression in adult fast fibers results from repression of specific isoforms by innervation.     

Myosin heavy chain isoforms in histochemically defined fiber types of rat muscle

Summary Combined histochemical and biochemical analyses were performed on rat skeletal muscles in order to determine the myosin heavy chain patterns in specific fiber types. Four myosin heavy chain isoforms were separated by gradient polyacrylamide gel electrophoresis of extracts from single fibers and whole muscle homogenates. Their electrophoretic mobility increased in the order HCIIa, HCIIb, and HCI. HCIIa, HCIIb and HCI were present as unique isoforms in histochemically defined fiber types IIA, IIB and I, respectively. The isoforms HCI and HCIIa coexisted at variable ratios in type IC and IIC fibers. An additional fast myosin heavy chain isoform with an electrophoretic mobility between HCIIa and HCIIb was designated as HCIId because of its abundance in fast fibers of large diameter in the diaphragm. With the exception of slight differences in mATPase staining intensity after acid preincubation, these fibers were almost indistinguishable from type IIB fibers. In view of their specific myosin heavy chain composition (HCIId), these fibers were named type IID. In the extensor digitorum longus muscle, type IID fibers were of smaller size than type IIB and differed from the latter by higher NADH tetrazolium reductase activities. Circumstantial evidence suggests that type IID fibers are identical with the 2X fibers, previously described by Schiaffino et al. (1986).     

Myosin heavy chain isoforms in histochemically defined fiber types of rat muscle

Combined histochemical and biochemical analyses were performed on rat skeletal muscles in order to determine the myosin heavy chain patterns in specific fiber types. Four myosin heavy chain isoforms were separated by gradient polyacrylamide gel electrophoresis of extracts from single fibers and whole muscle homogenates. Their electrophoretic mobility increased in the order HCIIa, HCIIb, and HCI. HCIIa, HCIIb and HCI were present as unique isoforms in histochemically defined fiber types IIA, IIB and I, respectively. The isoforms HCI and HCIIa coexisted at variable ratios in type IC and IIC fibers. An additional fast myosin heavy chain isoform with an electrophoretic mobility between HCIIa and HCIIb was designated as HCIId because of its abundance in fast fibers of large diameter in the diaphragm. With the exception of slight differences in mATPase staining intensity after acid preincubation, these fibers were almost indistinguishable from type IIB fibers. In view of their specific myosin heavy chain composition (HCIId), these fibers were named type IID. In the extensor digitorum longus muscle, type IID fibers were of smaller size than type IIB and differed from the latter by higher NADH tetrazolium reductase activities. Circumstantial evidence suggests that type IID fibers are identical with the 2X fibers, previously described by Schiaffino et al. (1986).     

Relationship between myosin heavy chain IId isoform and fibre types in soleus muscle of the rat after hindlimb suspension

The relationship between the myosin heavy chain (HC) IId isoform and histochemically defined fibre types was investigated in the rat soleus muscle after hindlimb suspension. After 4 weeks of suspension, right and left muscles were removed and fibre type composition and total fibre number were examined by histochemical myosin adenosine triphosphatase staining sections. Myosin HC isoforms were analysed by sodium dodecyl sulphate polyacrylamide gel electrophoresis. After the suspension, there was a significant decrease in the percentage of type I fibres and a concomitant increase in that of type IIa fibres. However, the total number of fibres was not affected by suspension. The synthesis of HC IId isoform, which was not found in the control, and the decrease in the ratio of slow type myosin heavy chain isoform (HC I) were observed after suspension. These results would may suggest that the change of fibre type composition was caused by a shift from type I to IIa fibres after suspension. Furthermore, it could be suggested that the synthesis of HC IId isoform occurred during the stage of type shift from type I to IIa fibres.     

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

Summary 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 HC 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.     

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.     

Developmental appearance of myosin heavy and light chain isoforms in vivo and in vitro in chicken skeletal muscle

Three myosin heavy chain isoforms with unique peptide maps appear sequentially in the development of the chicken pectoralis major muscle. An embryonic isoform is expressed early and throughout development in the embryo. A second isoform appears just after hatching and predominates by 10 days ex ovo. A third isoform, indistinguishable from adult myosin heavy chain, predominates by 8 weeks after hatching. This sequence of myosin isoform change does not, however, appear during myogenesis in vitro. In cultures prepared from embryonic myoblasts only embryonic myosin heavy chain is expressed. This is true even in cultures maintained for 30 days. Myosin light chain expression also changes in vivo with a progressive increase in fast light chain 3 accumulation. In vitro, however, this shift to increasing fast light chain 3 accumulation does not occur. The results indicate that the myosin heavy chain and light chain pattern observed in vitro is identical to that of the embryonic muscle and that the conditions necessary for the shift in expression to a more mature myosin phenotype are not present in myogenic cultures. These cultures are therefore potentially of great value in probing further the neural and humoral determinants of muscle fiber maturation and growth.     

Subunit composition of rodent isomyosins and their distribution in hindlimb skeletal muscles

Three adult skeletal muscle sarcomeric myosin heavy chain (MHC) genes have been identified in the rat, suggesting that the expressed native myosin isoforms can be differentiated, in part, on the basis of their MHC composition. This study was undertaken to ascertain whether the five major native isomyosins [3 fast (Fm1, Fm2, Fm3), 1 slow (Sm), and 1 intermediate (Im)], typically expressed in the spectrum of adult rat skeletal muscles comprising the hindlimb, could be further differentiated on the basis of their MHC profiles in addition to their light chain composition. Results show that in muscles comprised exclusively of fast-twitch glycolytic (FG) fibers and consisting of Fm1, Fm2, and Fm3, such as the tensor fasciae latae, only one MHC, designated as fast type IIb, could be resolved. In soleus muscle, comprised of both slow-twitch oxidative and fast-twitch oxidative-glycolytic fibers and expressing Sm and Im, two MHC bands were resolved and designated as slow/cardiac beta-MHC and fast type IIa MHC. In muscles expressing a mixture of all three fiber types and a full complement of isomyosins, as seen in the plantaris, the MHC could be resolved into three bands. Light chain profiles were characterized for each muscle type, as well as for the purified isomyosins. These data suggest that Im (IIa) consists of a mixture of fast and slow light chains, whereas Fm (IIb) and Sm (beta) isoforms consist solely of fast- and slow-type light chains, respectively. Polypeptide mapping of denatured myosin extracted from muscles expressing contrasting isoform phenotypes suggests differences in the MHC primary structure between slow, intermediate, and fast myosin isotypes. These findings demonstrate that 1) Fm, Im, and Sm isoforms are differentiated on the bases of both their heavy and light chain components and 2) each isomyosin is distributed in a characteristic fashion among rat hindlimb skeletal muscles. Furthermore, these data suggest that the ratio of isomyosins in a given muscle or muscle region is of physiological importance to the function of that muscle during muscular activity.     

An alternative domain near the ATP binding pocket of Drosophila myosin affects muscle fiber kinetics

We examined the importance of alternative versions of a region near the ATP binding site of Drosophila myosin heavy chain for muscle mechanical properties. Previously, we exchanged two versions of this region (encoded by alternative exon 7s) between the indirect flight muscle myosin isoform (IFI) and an embryonic myosin isoform (EMB) and found, surprisingly, that in vitro solution actin-activated ATPase rates were increased (higher Vmax) by both exon exchanges. Here we examined the effect of increased ATPase rate on indirect flight muscle (IFM) fiber mechanics and Drosophila locomotion. IFM expressing EMB with the exon 7a domain replaced by the IFM specific exon 7d domain (EMB-7d) exhibited 3.2-fold greater maximum oscillatory power (Pmax) and 1.5-fold greater optimal frequency of power generation (fmax) versus fibers expressing EMB. In contrast, IFM expressing IFI with the exon 7d region replaced by the EMB exon 7a region (IFI-7a), showed no change in Pmax, fmax, step response, or isometric muscle properties compared to native IFI fibers. A slight decrement in IFI-7a flight ability was observed, suggesting a negative influence of the increased ATPase rate on Drosophila locomotion, perhaps due to energy supply constraints. Our results show that exon 7 plays a substantial role in establishing fiber speed and flight performance, and that the limiting step that sets ATPase rate in Drosophila myosin has little to no direct influence in setting fmax for fast muscle fiber types.     

Assembly of avian skeletal muscle myosins: evidence that homodimers of the heavy chain subunit are the thermodynamically stable form

Using a double antibody sandwich ELISA we examined the heavy chain isoform composition of myosin molecules isolated from chicken pectoralis major muscle during different stages of development. At 2- and 40-d posthatch, when multiple myosin heavy chain isoforms are being synthesized, we detected no heterodimeric myosins, suggesting that myosins are homodimers of the heavy chain subunit. Chymotryptic rod fragments of embryonic, neonatal, and adult myosins were prepared and equimolar mixtures of embryonic and neonatal rods and neonatal and adult rods were denatured in 8 M guanidine. The guanidine denatured myosin heavy chain fragments were either dialyzed or diluted into renaturation buffer and reformed dimers which were electrophoretically indistinguishable from native rods. Analysis of these renatured rods using double antibody sandwich ELISA showed them to be predominantly homodimers of each of the isoforms. Although hybrids between the different heavy chain fragments were not detected, exchange was possible under these conditions since mixture of biotinylated neonatal rods and fluoresceinated neonatal rods formed a heterodimeric biotinylated-fluoresceinated species upon renaturation. Therefore, we propose that homodimers are the thermodynamically stable form of skeletal muscle myosin isoforms and that there is no need to invoke compartmentalization or other cellular regulatory processes to explain the lack of heavy chain heterodimers in vivo.     

Distribution of myosin isoenzymes among skeletal muscle fiber types.

Using an immunocytochemical approach, we have demonstrated a preferential distribution of myosin isoenzymes with respect to the pattern of fiber types in skeletal muscles of the rat. In an earlier study, we had shown that fluorescein-labeled antibody against "white" myosin from the chicken pectoralis stained all the white, intermediate and about half the red fibers of the rat diaphragm, a fast-twitch muscle (Gauthier and Lowey, 1977). We have now extended this study to include antibodies prepared against the "head" (S1) and "rod" portions of myosin, as well as the alkali- and 5,5'dithiobis (2-nitrobenzoic acid) (DTNB)-light chains. Antibodies capable of distinguishing between alkali 1 and alkali 2 type myosin were also used to localize these isoenzymes in the same fast muscle. We observed, by both direct and indirect immunofluorescence, that the same fibers which had reacted previously with antibodies against white myosin reacted with antibodies to the proteolytic subfragments and to the low molecular-weight subunits of myosin. These results confirm our earlier conclusion that the myosins of the reactive fibers in rat skeletal muscle are sufficiently similar to share antigenic determinants. The homology, furthermore, is not confined to a limited region of the myosin molecule, but includes the head and rod portions and all classes of light chains. Despite the similarities, some differences exist in the protein compositions of these fibers: antibodies to S1 did not stain the reactive (fast) red fiber as strongly as they did the white and intermediate fibers. Non-uniform staining was also observed with antibodies specific for A2 myosin; the fast red fiber again showed weaker fluorescence than did the other reactive fibers. These results could indicate a variable distribution of myosin isoenzymes according to their alkali-light chain composition among fiber types. Alternatively, there may exist yet another myosin isoenzyme which is localized in the fast red fiber. Those red fibers which did not react with any of the antibodies to pectoralis myosin, did react strongly with an antibody against myosin isolated from the anterior latissimus dorsi (ALD), a slow red muscle of the chicken. The myosin in these fibers (slow red fibers) is, therefore, distinct from the other myosin isoenzymes. In the rat soleus, a slow-twitch muscle, the majority of the fibers reacted only with antibody against ALD myosin. A minority, however, reacted with antiboddies to pectoralis as well as ALD myosin, which indicates that both fast and slow myosin can coexist within the same fiber of a normal adult muscle. These immunocytochemical studies have emphasized that a wide range of isoenzymes may contribute to the characteristic physiological properties of individual fiber types in a mixed muscle.     

Changes in myosin heavy chain isoforms during chronic low-frequency stimulation of rat fast hindlimb muscles. A single-fiber study

Fast-twitch rat muscles contain three fast myosin heavy chains (HC) which can be separated by density gradient gel electrophoresis. Their mobility increases in the order of HCIIa less than HCIId less than HCIIb. In contrast to the rabbit, where chronic low-frequency nerve stimulation induces a fast-to-slow conversion, stimulation for up to 56 days does not lead to appreciable increases in the relative concentration of the slow myosin heavy chain HCI in rat fast-twitch muscles. However, chronic stimulation of rat fast-twitch muscle does evoke a rearrangement of the fast myosin heavy chain isoform pattern with a progressive decrease in HCIIb and progressive increases in HCIIa and HCIId. As judged from the time course and extent of these transitions, it appears that HCIId is an intermediate form between HCIIb and HCIIa. Single-fiber analyses of normal muscles make it possible to assign these heavy chain isoforms to histochemically defined fiber types IIB, IID, and IIA. The stimulation-induced fiber transformations produce numerous hybrid fibers displaying more than one myosin heavy chain isoform. Some transforming fibers contain up to four different myosin heavy chain isoforms.     

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.     

Muscle Fiber Types in the Pectoralis of the White Pelican,a Soaring Bird

The pectoralis muscle (M. pectoralis) of many premier soaring birds contains a smaller, accessory, deep belly in addition to the much larger superficial belly found in all flying birds. Here we describe the muscle fiber types in both the superficial and deep bellies of the pectoralis of one such adept soaring species, the white pelican (Pelecanus erythrorhynchos).Histochemical techniques are used to demonstrate both nicotinamide adenine dinucleotide (reduced) and myofibrillar adenosine triphosphatase activities within the muscle fibers. Immunocytochemical methods employing several monoclonal antibodies, each directed against a different myosin heavy chain epitope of the chicken, are also used to characterize the fibers. While the superficial belly of the muscle consists entirely of fast-twitch oxidative-glycolytic fibers, the deep belly is composed exclusively of slow fibers. These slow fibers are labelled by two different antibodies specific for chicken slow myosin. We suggest that the fibers of the superficial belly are best suited to flapping flight, and that the fibers of the deep belly would be recruited only during soaring flight. Furthermore, we hypothesize that the deep belly found in the pectoralis of soaring species probably evolved from a deep neuromuscular compartment of the superficial belly.     

Changes in myosin isozymes during development of chicken breast muscle

The patterns of myosin isozymes in embryonic and adult chicken pectoralis muscle were examined by electrophoresis in a non-denaturing gel system (pyrophosphate acrylamide gel electrophoresis), and both light chains and heavy chains of embryonic and adult myosin isozymes were compared. In pyrophosphate acrylamide gel electrophoresis, the predominant isozyme component in embryonic pectoralis myosin could be clearly distinguished from adult myosin isozymes. SDS-polyacrylamide gel electrophoresis indicated that the light chain composition of embryonic myosin was also different from that of adult myosin. The pattern of peptide fragments produced by myosin digestion with a-chymotrypsin differed significantly between embryonic and adult skeletal myosin. These results suggest that myosin in the embryonic pectoralis muscle is different in both light and heavy chain composition from myosin in the same adult tissue.     

Analysis of myosin light and heavy chain types in single human skeletal muscle fibers

In this study, myosin types in human skeletal muscle fibers were investigated with electrophoretic techniques. Single fibers were dissected out of lyophilized surgical biopsies and typed by staining for myofibrillar ATPase after preincubation in acid or alkaline buffers. After 14C-labelling of the fiber proteins in vitro by reductive methylation, the myosin light chain pattern was analysed on two-dimensional gels and the myosin heavy chains were investigated by one-dimensional peptide mapping. Surprisingly, human type I fibers, which contained only the slow heavy chain, were found to contain variable amounts of fast myosin light chains in addition to the two slow light chains LC1s and LC2s. The majority of the type I fibers in normal human muscle showed the pattern LC1s, LC2s and LC1f. Further evidence for the existence in human muscle of a hybrid myosin composed of a slow heavy chain with fast and slow light chains comes from the analysis of purified human myosin in the native state by pyrophosphate gel electrophoresis. With this method, a single band corresponding to slow myosin was obtained; this slow myosin had the light chain composition LC1s, LC2s and LC1f. Type IIA and IIB fibers, on the other hand, revealed identical light chain patterns consisting of only the fast light chains LC1f, LC2f and LC3f but were found to have different myosin havy chains. On the basis of the results presented, we suggest that the histochemical ATPase normally used for fibre typing is determined by the myosin heavy chain type (and not by the light chains). Thus, in normal human muscle a number of 'hybrid' myosins were found to occur, namely two extreme forms of fast myosins which have the same light chains but different heavy chains (IIA and IIB) and a continuum of slow forms consisting of the same heavy chain and slow light chains with a variable fast light chain composition. This is consistent with the different physiological roles these fibers are thought to have in muscle contraction.     

Heterogeneity of fast-oxidative muscle fibers of chicken demonstrated by anti-myosin monoclonal antibodies

Summary The fiber type composition of two fast muscles of the chicken, namely, adductor superficialis (AS) and pectoralis major (PM) was examined by the histochemical myosin ATPase staining and immunochemical techniques using monoclonal antibodies (McAbs). Two new McAbs produced against the myosin of the anterior latissimus dorsi (ALD) muscle of the chicken and named ALD-122 and ALD-83 were characterized to be specific for myosin heavy chain (MHC) and for myosin light chain-1 respectively. They were used in conjunction with previously reported McAbs specific for slow MHC (ALD-47), fast MHC (MF-14) and fast light chain-2 (MF-5). By the histochemical ATPase test most muscle fibers of AS and PM muscles reacted as IIA and IIB respectively. By immunofluorescent staining with the anti-MHC McAbs, ALD-122, and MF-14, the fibers of AS, muscle showed remarkable heterogeneity whereas PM muscle fibers reacted, uniformly. Differences in the myosin light chain composition of AS and PM muscles were also found by SDS-gel electrophoresis and immunoblot analysis with the anti-light chain McAb, ALD-83. The study clearly indicated that the histochemically homogenous (type IIA) AS muscle is composed of several subpopulations of fibers which differ in their myosin composition and that this heterogeneity of the muscle is not simply due to presence of variable amounts of slow myosin in its fibers.