Histoenzymatic characterization of sub-types of type I fibres in fast muscles of rats

Metachromatic procedure for fiber typing in chicken skeletal muscle

Metachromatic staining of anterior latissimus dorsi, posterior latissimus dorsi, and sartorius muscles of domestic chicken with azure A and toluidine blue produced differentiation of muscle fiber types. The procedure is rapid, with optimum results obtained after 2 to 5 min incubation and 5 to 10 s of staining. Reaction of serial sections for myosin Ca++-adenosine triphosphatase with the usual procedure showed that the same fibers were typed similarly with both methods.

Determination of fiber types of chicken skeletal muscles based on reaction for actomyosin, calcium+2, magnesium+2-dependent adenosine triphosphatase

Muscle fiber subtypes, determined with the actomyosin Ca+2,Mg+2-adenosine triphosphatase (ATPase) reaction in chicken anterior latissimus dorsi and posterior latissimus dorsi muscles, were demonstrated only after acid or alkaline preincubation followed by a 60-min enzyme incubation. In contrast, subtypes were demonstrated in the sartorius muscle either with or without preincubation. A single-step procedure was therefore possible with this muscle. The results were generally similar to those obtained previously with the mycosin Ca+2-ATPase procedure. Both methods revealed corresponding muscle fiber subtypes, with the exceptions noted below. The actomyosin Ca+2,Mg+2-ATPase procedure, following preincubation at pH 9.4 and 10.3, resulted in a similar reaction intensity in all fiber types. With the myosin Ca+2-ATPase procedure, the IRA (slow) type in anterior latissimus dorsi and sartorius muscles and the I (slow), IIR (fast oxidative-glycolytic), and IIW (fast glycolytic) types in posterior latissimus dorsi muscle had a higher reaction intensity following preincubation at pH 9.4 than at pH 10.3. Fiber Types IIR and IIW in sartorius muscle were easily distinguished with the actomyosin Ca+2,Mg+2-ATPase procedure.

Histochemical heterogeneity of intrafusal muscle fibres in slow and fast skeletal muscles of the rat

Intrafusal muscle fibres of the slow soleus (Sol) and fast vastus lateralis (VL) muscles of the rat were studied histochemically. Serial transverse sections were incubated for the localization of succinate dehydrogenase (SDH), alpha glycerophosphate dehydrogenase (GPD) and adenosine triphosphatase (ATPase). The latter was examined further after preincubation in acidic solution held at either low or room temperature (RT). The bag2 intrafusal fibres in both muscles displayed high regular and acid stable ATPase, but low SHD and GPD activities. Bag1 intrafusal fibres showed low to moderate regular ATPase, a regional heterogeneity after RT acid preincubation (low activity in juxtaequatorial and high in polar zones), moderate SDH, but low GPD reactions. In both muscles the chain fibres usually exhibited high ATPase for both regular and cold acid preincubated reactions, but usually low activity after RT acid preincubation; they had high SDH but variable GPD activities. In Sol muscle, however, approximately 25% of spindles contained chain fibres that showed high acid-stable ATPase reaction after both cold and RT acid preincubation. In contrast, chain fibres in some VL spindles had a characteristically low ATPase reaction even after cold acid preincubation. This study, therefore, has delineated the existence of an inherent heterogeneity among chain fibres (with respect to their histochemical reactions) in muscle spindles located within slow and fast muscles and also between those found within populations of either Sol or VL muscle spindles.

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.

Neural control of phenotypic expression in mammalian muscle fibers

In this review, the present knowledge about the mechanisms involved in the control of the phenotypic expression of mammalian muscle fibers is summarized. There is a discussion as to how the activity imposed on the muscle fibers by the motoneuron finally induces in the muscle cells the expression of those genes that define its particular phenotype. The functional and molecular heterogeneity of skeletal muscle is thus defined by the existence of motor units with varied function, while the homogeneity of muscle fibers belonging to the same motor unit is yet another indication of the importance of activity in the control of gene expression of the mammalian muscle fiber.

Histochemical properties of the biventer cervicis muscle of the chick: a relationship between multiple innervation and slow-tonic fibre types

Chick biventer cervicis muscle fibres have been studied histochemically. Fast-twitch, focally innervated (alpha) fibres represent 70-80% of the total fibres in this muscles. Two histochemical profiles of slow-tonic multi-innervated (beta) fibres have been observed from embryonic life the adult (three-months) stage. These two slow-tonic types differ in the activity of their histochemically demonstrated myofibrillar ATPase after either acid or alkaline preincubation, and after formalin fixation. Both slow-tonic fibre types have a high oxidative metabolism and are PAS-negative. They are referred as to beta 1 and beta 2R fibre types (slow-tonic oxidative) in an expansion of Ashmore's nomenclature, and compared to avian slow-tonic sub-types that have been described in recent reports. beta 1 and beta 2 fibre types exhibit a similar pattern of innervation. Possible explanations of the origin of histochemical heterogeneity in multiple innervated fibres are discussed.

A histoenzymatic study of rat intrafusal muscle fibres

The histochemical activities of myofibrillar adenosine triphosphatase (ATPase), succinic dehydrogenase (SDH) and alpha glycerophosphate dehydrogenase (alpha-GPD) were studied in intrafusal muscle fibres of rat fast and slow muscles. The ATPase reaction was carried out after the three standard acid preincubations. The cold K2-EDTA preincubated ATPase reaction product was similar to that seen following the regular or alkali-preincubated ATPase reaction, except that the intermediate bag fibres exhibited much higher activity after cold K2-EDTA preincubation. Following either acetic acid solution or cold and room temperature K2-EDTA-preincubation, followed by the ATPase reaction, chain fibres of the fast muscles vastus lateralis and extensor digitorum longus exhibited a very low amount of reaction product as compared with those of the slow soleus. Veronal acetate and K2-EDTA preincubations (and equally preincubation in acetic acid solution) resulted in acid stable ATPase activity along the entire length of the typical bag fibres but only in the polar regions of the intermediate bag fibres. On the basis of differing alpha-GPD reaction, two sub populations of nuclear chain fibres were discovered in one spindle. It is a matter of conjecture, to what extent the histochemical differences of intrafusal fibres from fast and slow muscles reflects functional distinctions in the response to stretch of muscle spindles from fast and slow muscles.

Variable pH dependence of the myosin-ATPase in different muscles of the rat

For the histochemical demosntration of the Myosin-ATPase (EC 3.6.1.3) the pH of both the preincubation and the incubation medium was varied in steps of 1 within a range: 10.2 to 10.5 and 9.3 to 9.9, respectively. The optimum combinations of both pH values, defined as the ones providing most consistent contrast among the three major types of muscle fibers were determined in 9 different muscles of the rat. The spectrum of optimum combinations differs considerably from muscle to muscle. The reduction of the incubation pH by only 0.1 may drastically change the staining pattern. This probably reflects the unspecificity of the histochemical procedure as well as the plasticity of the ATPase systems. To cope with the lability of the myosin-ATPase the optimum pH values of both media should be determined for each muscle separately.

Histochemical and ultrastructural characteristics of a new muscle fibre type in avian striated muscle

The serratus metapatagialis (SMP) muscle of the pigeon has been studied histochemically and ultrastructurally. At the gross anatomical level the SMP is clearly divisible into a peripheral whitish band and a red portion comprised predominantly of 'pale' and 'red' fibres respectively. The pale fibres possess low succinate dehydrogenase, low mitochondrial content, absence of subsarcolemmal mitochondrial aggregates, low fat, moderate glycogen, high phosphorylase, low-to-moderate regular myofibrillar adenosine triphosphatase (M-ATPase), activation of M-ATPase following acid preincubation and jagged Z bands. On the basis of these characteristics, these physiologically slow muscle fibres have been termed 'Type I white or slow-twitch glycolytic'. The SMP red fibres, however, possess high aerobic as well as glycolytic capacity, high M-ATPase activity which is labile after acid preincubation and thick but straight Z bands; therefore, they are the 'Type II red or fast-twitch oxidative-glycolytic'.

A histochemical study of denervated marsupial hemidiaphragm

The marsupial (quokka) hemidiaphragm showed postdenervation hypertrophy and subsequent atrophy. The type II muscle fibres hypertrophied up to 20 days postoperation and then regressed. However, the type I fibres hypertrophied throughout the experimental period (100 days) studied. Unlike denervated eutherian hemidiaphragm, fibre-splitting was absent in the denervated marsupial muscle. An enhancement of the ATPase reaction in the denervated type I fibres may be due to dedifferentiation. Presumably innervation exerts a 'negative control' and prevents increase of type I fibre size in the normal hemidiaphragm.

Changes in ATPase and SDH reactions of the rat extrafusal and intrafusal muscle fibres after preincubations at different pH

The dependence of adenosine-triphosphatase (ATPase) and succinic dehydrogenase (SDH) histochemical reactions on the pH of the preincubation medium was studied in serial cross sections of 1- to 6-month-old rat extensor digitorum longus (EDL) and soleus (SOL) muscles. The use of a wide spectrum of pH values confirmed the previous results showing that: (1) according to their ATPase and SDH reactions 3 types of extrafusal muscle fibres, i.e., fast-twitch glycolytic (FG), fast-twitch oxidative-glycolytic (FOG) and slow-twitch oxidative (SO) and 3 types of intrafusal muscle fibres, i.e. typical and intermediate nuclear bag fibres and nuclear chain fibres were observed; (2) only acid preincubation (pH 4.35) is necessary to demonstrate the reversal of the ATPase reaction; while (3) alkali preincubation (pH 10.4) does not provide any new important information as compared with ATPase without preincubation. Furthermore, it was shown that: (4) fast-twitch muscle fibres exhibited high ATPase activity on preincubations at pH 4.9 to 10.4, slow-twitch fibres had very high ATPase activity on preincubation at pH 4.3 and 4.5; (5) after preincubation at pH 4.5 two types of FOG fibres were observed, differing in their ATPase activity; (6) in both muscles there were fibres with intermediate ATPase activity both after acid and/or alkali preincubations; (7) the intrafusal muscle fibres exhibited some specific characteristics when compared with extrafusal fibres. In contrast to the ATPase reactions, SDH activity was decreased equally, in both extra- and intrafusal fibres, with increasing acidity and alkality of the preincubation medium.