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1.
Myosin heavy chain isoform composition in striated muscle after denervation and self-reinnervation 总被引:2,自引:0,他引:2
A Jakubiec-Puka J Kordowska C Catani U Carraro 《European journal of biochemistry》1990,193(3):623-628
The total content of myosin heavy chains (MHC) and their isoform pattern were studied by biochemical methods in the slow-twitch (soleus) and fast-twitch (extensor digitorum longus) muscles of adult rat during atrophy after denervation and recovery after self-reinnervation. The pattern of fibre types, in terms of ultrastructure, was studied in parallel. After denervation, total MHC content decreased sooner in the slow-twitch muscle than in the fast-twitch. The ratio of MHC-1 and the MHC-2B isoforms to the MHC-2A isoform decreased in the slow and the fast denervated muscles, respectively. After reinnervation of the slow muscle, the normal pattern of MHC recovered within 10 days and the type 1 isoform increased above the normal. In the reinnervated fast muscle, the 2B/2A isoform ratio continued to decrease. Traces of the embryonic MHC isoform, identified by immunochemistry, were found in both denervated and reinnervated slow and fast muscles. A shift in fibre types was similar to that found in the MHC isoforms. Within 2 months of recovery a tendency to normalization was observed. The results show that (a) MHC-2B isoform and the morphological characteristics of the 2B-type muscle fibres are susceptible to lack of innervation, similar to those of type 1, (b) during muscle recovery induced by reinnervation the MHC isoforms and muscle fibres shift transiently to type 1 in the soleus and to type 2A in the extensor digitorum longus muscles, and (c) the embryonic isoform of MHC may appear in the adult skeletal muscles if innervation is disturbed. 相似文献
2.
I A Boyd 《Quarterly journal of experimental physiology and cognate medical sciences》1976,61(3):203-254
1. The mechanical behaviour of intrafusal muscle fibres during fusimotor stimulation and passive stretch was observed directly in muscle spindles isolated from the cat tenuissimus muscle. 2. Mammalian intrafusal muscle fibres are of three functional types. Most spindles contain one slow nuclear bag fibre, one fast nuclear bag fibre, and four or five nuclear chain fibres. 3. Contraction in slow nuclear bag fibres is characterized by a long latency and very slow initial velocity, whereas the latency for the other intrafusal fibres is short and the inital velocity rapid. The mean time for maximum contraction (at 75 Hz to 100 Hz) and relaxation is significantly longer for slow nuclear bag fibres (0-8s) than for other intrafusal fibres (0-5 s). The contraction time of fast nuclear bag fibres is sometimes longer than that of nuclear chain fibres but the mean values are not significantly different; a difference in the time to attain 90% contraction is more obvious. 4. At low stimulation frequencies (10 Hz) contraction in slow nuclear bag fibres and in most fast nuclear bag fibres is smooth whereas nuclear chain fibres exhibit marked oscillations. Single stimuli elicit small local twitches in nuclear chain fibres and occasionally in fast nuclear bag fibres but produce no visible effect in slow nuclear bag fibres. 5. Maximum contraction of slow and fast nuclear bag fibres at body temperature is attained at a stimulation frequency of 75 Hz to 100 Hz, whereas a frequency of 150 Hz or more is required for maximum contraction of nuclear chain fibres. At 50 Hz at body temperature contraction in nuclear bag fibres is at least half the maximum, whereas in many spindles nuclear chain fibres show only a very small contraction at this frequency. 6. Contraction in slow nuclear bag fibres occurs at one or two discrete foci, most of which lie in the intracapsular region beyond the end of the fluid space. Weak contraction extends the primary sensory spiral by a small amount (2%-8%) at a low velocity (5%-10%s-1). When the fibre is passively stretched the spiral opens and then creeps back to about 75% of the extension at the end of the stretch due to yielding in the poles of fibre; creep is complete in 0-5s to 2-5s. 7. Contraction in fast nuclear bag fibres also occurs at one or two discrete foci, most of which lie in the intracapsular region beyond the end of the fluid space. Shortening of sarcomeres at the foci and extension of the sensory spiral are, however, up to eight times greater (up to 25%) than in slow nuclear bag fibres, and the velocity of stretch of the spiral is three to eight times greater (25%-40%s-1). Fast nuclear bag fibres exhibit little or no creep following passive stretch. 8. Contraction in the nuclear chain fibre bundle is localized to the intracapsular region, centered on a point in the intracapsular region between 0-9 mm and 1-6 mm from the spindle equator. Maximal contraction stretches primary and secondary sensory endings by 15% to 20%, at 30% to 40% s-1... 相似文献
3.
Tomás Soukup Fatima Pedrosa-Domellöf Lars-Eric Thornell 《Differentiation; research in biological diversity》1993,53(1):35-43
Abstract. The myofibrillar ATPase (mATPase) activity and the pattern of expression of several myosin heavy chain (MHC) isoforms and of M-protein (Mr 165000) were studied in serial cross sections of neonatally deefferented 5- to 8-week-old rat hindlimb muscle spindles with supernumerary intrafusal fibres. In a sample of 5- to 6-week-old neonatally deefferented muscle spindles cut through the A region, the average number of intrafusal fibres per spindle was 8.4 in comparison to 4.2 in control spindles. Parent fibres extended throughout the whole encapsulated portion of the spindle, whereas supernumerary fibres were found only in the A region. The diameters of the supernumerary intrafusal fibres varied from less than 1 μ up to 10 μ approximately. On the basis of the mATPase activity and the pattern of expression of MHC isoforms and of M-protein, the vast majority of the supernumerary fibres could be classified as nuclear bag2 , bag1 or chain fibres. However, some supernumerary fibres with small diameters exhibited features that did not fit any of the three known intrafusal fibre types. Two major processes, namely fibre splitting versus activation and fusion of satellite cells, might account for the formation of supernumerary fibres. The data presented suggest the existence of at least two types of intrafusal satellite cells. One type of satellite cell is related to the nuclear bag fibres and gives rise to myotubes which, if they have sensory innervation, can express slow tonic MHC and, therefore, differentiate into a phenotype similar to that seen in nuclear bag fibres. The other type of satellite cells form myotubes which attain a fast phenotype similar to that seen in nuclear chain fibres irrespective of the presence or absence of sensory innervation. 相似文献
4.
Erika Snoj-Cvetko Janez Sketelj Igor Dolenc Slavko Obreza Chantal Janmot Anne d'Albis Ida Eržen 《Histochemistry and cell biology》1996,106(5):473-479
The hypothesis that the limited adaptive range observed in fast rat muscles in regard to expression of the slow myosin is
due to intrinsic properties of their myogenic stem cells was tested by examining myosin heavy chain (MHC) expression in regenerated
rat extensor digitorum longus (EDL) and soleus (SOL) muscles. The muscles were injured by bupivacaine, transplanted to the
SOL muscle bed and innervated by the SOL nerve. Three months later, muscle fibre types were determined. MHC expression in
muscle fibres was demonstrated immunohistochemically and analysed by SDS-glycerol gel electrophoresis. Regenerated EDL transplants
became very similar to the control SOL muscles and indistinguishable from the SOL transplants. Slow type 1 fibres predominated
and the slow MHC-1 isoform was present in more than 90% of all muscle fibres. It contributed more than 80% of total MHC content
in the EDL transplants. About 7% of fibres exhibited MHC-2a and about 7% of fibres coexpressed MHC-1 and MHC-2a. MHC-2x/d
contributed about 5–10% of the whole MHCs in regenerated EDL and SOL transplants. The restricted adaptive range of adult rat
EDL muscle in regard to the synthesis of MHC-1 is not rooted in muscle progenitor cells; it is probably due to an irreversible
maturation-related change switching off the gene for the slow MHC isoform.
Accepted: 11 June 1996 相似文献
5.
Summary A quantitative histochemical technique was developed for determining the kinetics of the calcium-activated myosin ATPase (Ca2+-myosin ATPase) reaction in rat skeletal muscle fibres. Using this technique, the maximum velocity (Vmax) and the apparent Michaelis-Menten rate constant for ATP (Kapp) of the Ca2+-myosin ATPase reaction were measured in type-identified fibres of the rat medial gastrocnemius (MG) muscle. The Vmax and the Kapp of the Ca2+-myosin ATPase reaction were lowest in type I fibres and highest (i.e., approx. two times greater) in type IIb fibres. The Kapp in type IIa fibres was similar to that in type I. However, the Vmax was 1.5 times greater in type IIa fibres, compared to type I fibres. Evidence is presented to suggest that the type IIb fibre population in the MG does not represent a single myosin isozyme. In addition, the broad range of Vmax and Kapp values indicates that there is marked heterogeneity in the myosin heavy chain and myosin light chain composition of myosin isozymes among individual fibres. 相似文献
6.
Soukup T Thornell LE 《Physiological research / Academia Scientiarum Bohemoslovaca》1999,48(6):519-523
We have studied the morphology and pattern of expression of myosin heavy chain (MHC) isoforms of intrafusal fibres in a human first lumbrical muscle. Each intrafusal fibre type, namely nuclear bag1, nuclear bag2 and nuclear chain fibres, had a distinct MHC composition and distribution of different MHC isoforms along the whole length of intrafusal fibres. However, most muscle spindles analyzed also contained one or several intrafusal fibres exhibiting an extrafusal or mixed pattern of immunoreactivity which did not correspond to any of the described intrafusal fibre types. We conclude that the latter fibres do not represent new intrafusal fibre types, but their morphology and expression of MHC merely reflects the differences in their innervation owing to their unusual localization at the edge or outside the axial bundle of intrafusal fibres. 相似文献
7.
Cellular adaptation of the trapezius muscle in strength-trained athletes 总被引:16,自引:4,他引:12
Kadi F Eriksson A Holmner S Butler-Browne GS Thornell LE 《Histochemistry and cell biology》1999,111(3):189-195
The aim of this study was to elucidate the cellular events that occur in the trapezius muscle following several years of
strength training. In muscle biopsies from ten elite power lifters (PL) and six control subjects (C), several parameters were
studied: cross-sectional area of muscle fibres, myosin heavy chain composition (MHC) and capillary supply [capillaries around
fibres (CAF) and CAF/fibre area]. A method was also developed for counting the number of myonuclei and satellite cell nuclei.
The proportion of fibres expressing MHC IIA, the cross-sectional area of each fibre type and the number of myonuclei, satellite
cells and fibres expressing markers for early myogenesis were significantly higher in PL than in C (P<0.05). A significant correlation between the myonuclear number and the cross-sectional area was observed. Since myonuclei
in mature muscle fibres are not able to divide, we suggest that the incorporation of satellite cell nuclei into muscle fibres
resulted in the maintenance of a constant nuclear to cytoplasmic ratio. The presence of small diameter fibres expressing markers
for early myogenesis indicates the formation of new muscle fibres.
Accepted: 17 November 1998 相似文献
8.
Summary The iliofibularis muscle ofXenopus laevis is reported to contain five types of fibres which have different force—velocity relationships. Ten fibres of each type were selected on the basis of succinate dehydrogenase activity, cross-sectional area and location in the muscle, in order to assess the validity of the fibre type classification.Maximum calcium-stimulated myofibrillar ATPase activity (V
max) and apparent Michaelis constant (K
m) for ATP were determined for these 50 fibres from serial sections. The values obtained varied according to the type of fibre. Type 1 had the highest and type 5 the lowest values forK
m andV
max.In a separate experiment, single freeze-dried fibres were used to determine the relationship between their ATP content and apparentK
m for ATP. There was a tendency for high ATP concentrations in fibres with highK
m values.When myofibrillar ATPase activity was related to the maximum velocity of shortening of the five fibre types, a significant correlation was found. It is concluded that calcium-stimulated myofibrillar ATPase histochemistry allows an estimate of the maximum shortening velocity of muscle fibres fromXenopus laevis. 相似文献
9.
Interrelationships of myofibrillar ATPase activity and metabolic properties of myosin heavy chain-based fibre types in rat skeletal muscle 总被引:2,自引:0,他引:2
Myofibrillar ATPase (mATPase), succinate dehydrogenase (SDH) and α-glycerophosphate dehydrogenase (GPD) activities and cross-sectional
area (CSA) were measured in fibres of rat medial gastrocnemius muscle using quantitative histochemistry. The same fibres were
typed immunohistochemically using monoclonal antibodies specific to selected myosin heavy chain (MHC) isoforms. The values
of mATPase, SDH, GPD and CSA formed a continuum, but significant differences in mean values were observed among fibre types
of presumed homogeneous MHC content. Type I fibres had the lowest mATPase activity, followed in rank order by type IIA<type
IID/X<type IIB. Type IIA fibres had the highest SDH activity, followed in rank order by type IID/X>type I>type IIB. The mean
GPD activity was consistently ranked according to fibre type such that type IIB>type IID/X >type IIA>type I. Type IIA fibres
were the smallest, type IIB fibres were the largest and types I and IID/X were of intermediate size. Significant interrelationships
between mATPase, SDH, GPD and CSA values were found on a fibre-to-fibre basis. Consequently, discrimination of fibres according
to their MHC content was possible on the basis of their mATPase, SDH, GPD and CSA profiles. These intrafibre interrelationships
suggest that the MHC isoform is associated with phenotypic differences in contractile, metabolic and size properties of muscle
fibre types.
Accepted: 30 November 1998 相似文献
10.
In order to evaluate the effects of fusimotor elimination on the expression of myosin heavy chain (MHC) proteins in intrafusal fibres, we compared the muscle spindles in hind limb muscles of 3- to 6-week-old rats de-efferented at birth with those of their litter-mate controls. Serial sections were labelled with antibodies against slow tonic, slow twitch, fast twitch and neonatal MHC isoforms, against synaptophysin, the neurofilament 68 kD subunit and laminin. We found that de-efferented intrafusal fibres differentiated, as in normal spindles, into nuclear bag and bag fibres both containing predominantly slow MHC, and nuclear chain fibres that contained fast and neonatal MHC. In both de-efferented and control intrafusal fibres the same MHCs were stained; the degree and extent of staining, however, varied. Both types of de-efferented bag fibres displayed a high content of slow tonic and slow twitch MHC along most of the fibre length, in contrast to the prominent regional variation in control bag fibres. In their encapsulated regions, the de-efferented bag fibres were more similar to each other in their reactivity to anti-fast twitch and anti-neonatal MHC antibodies than the control bag fibres. In these aspects they resembled more closely the bag fibres of newborn rats. The differences might be due to an arrest of "specialization" in the regional expression of the different MHC isoforms. Chain fibres developed MHC patterns identical to those of control spindles with all the antibodies used, even though they differentiated from the beginning in the absence of motor innervation. The structural differentiation of the capsule and sensory innervation in de-efferented muscle spindles, as shown by anti-laminin, anti-synaptophysin and anti-neurofilament staining, did not differ from the controls. We conclude, in agreement with previous studies, that the sensory innervation plays a key role in inducing and supporting the differentiation of intrafusal fibres and the specific expression of their MHC. However, we also show that motor innervation and/or muscle function seem to be necessary for the diversity in the expression and distribution of different slow and fast MHC isoforms in the bag and bag fibres. 相似文献
11.
Summary In order to evaluate the effects of fusimotor elimination on the expression of myosin heavy chain (MHC) proteins in intrafusal fibres, we compared the muscle spindles in hind limb muscles of 3- to 6-week-old rats de-efferented at birth with those of their litter-mate controls. Serial sections were labelled with antibodies against slow tonic, slow twitch, fast twitch and neonatal MHC isoforms, against synaptophysin, the neurofilament 68 kD subunit and laminin. We found that de-efferented intrafusal fibres differentiated, as in normal spindles, into nuclear bag1 and bag2 fibres both containing predominantly slow MHC, and nuclear chain fibres that contained fast and neonatal MHC. In both de-efferented and control intrafusal fibres the same MHCs were stained; the degree and extent of staining, however, varied. Both types of de-efferented bag fibres displayed a high content of slow tonic and slow twitch MHC along most of the fibre length, in contrast to the prominent regional variation in control bag fibres. In their encapsulated regions, the de-efferented bag fibres were more similar to each other in their reactivity to anti-fast twitch and anti-neonatal MHC antibodies than the control bag fibres. In these aspects they resembled more closely the bag fibres of newborn rats. The differences might be due to an arrest of specialization in the regional expression of the different MHC isoforms. Chain fibres developed MHC patterns identical to those of control spindles with all the antibodies used, even though they differentiated from the beginning in the absence of motor innervation.The structural differentiation of the capsule and sensory innervation in de-efferented muscle spindles, as shown by anti-laminin, anti-synaptophysin and anti-neurofilament staining, did not differ from the controls.We conclude, in agreement with previous studies, that the sensory innervation plays a key role in inducing and supporting the differentiation of intrafusal fibres and the specific expression of their MHC. However, we also show that motor innervation and/or muscle function seem to be necessary for the diversity in the expression and distribution of different slow and fast MHC isoforms in the bag1 and bag2 fibres. 相似文献
12.
Brian R. MacIntosh Walter Herzog Esther Suter J. Preston Wiley Jason Sokolosky 《European journal of applied physiology and occupational physiology》1993,67(6):499-506
It has been reported that there is a relationship between power output and fibre type distribution in mixed muscle. The strength of this relationship is greater in the range of 3–8 rad · s–1 during knee extension compared to slower or faster angular knee extensor speeds. A mathematical model of the force: velocity properties of muscle with various combinations of fast- and slow-twitch fibres may provide insight into why specific velocities may give better predictions of fibre type distribution. In this paper, a mathematical model of the force: velocity relationship for mixed muscle is presented. This model demonstrates that peak power and optimal velocity should be predictive of fibre distribution and that the greatest fibre type discrimination in human knee extensor muscles should occur with measurement of power output at an angular velocity just greater than 7 rad · s–1. Measurements of torque: angular velocity relationships for knee extension on an isokinetic dynamometer and fibre type distribution in biopsies of vastus lateralis muscles were made on 31 subjects. Peak power and optimal velocity were determined in three ways: (1) direct measurement, (2) linear regression, and (3) fitting to the Hill equation. Estimation of peak power and optimal velocity using the Hill equation gave the best correlation with fibre type distribution (r > 0.5 for peak power or optimal velocity and percentage of fast-twitch fibres). The results of this study confirm that prediction of fibre type distribution is facilitated by measurement of peak power at optimal velocity and that fitting of the data to the Hill equation is a suitable method for evaluation of these parameters. 相似文献
13.
A number of single fibres were isolated by dissection of four bovine masseter (ma) muscles, three rectus abdominis (ra) muscles and eight sternomandibularis (sm) muscles. By histochemical criteria these muscles contain respectively, solely slow fibres (often called type I), predominantly fast fibres (type II), and a mixture of fast and slow. The fibres were analysed by conventional sodium dodecyl sulphate/polyacrylamide-gel electrophoresis and the gels stained with Coomassie Blue. Irrespective of the muscle, every fibre could be classed into one of two broad groups based on the mobility of proteins in the range 135000-170000 daltons. When zones containing myosin heavy chain were cut from the single-fibre gel tracks and 'mapped' [Cleveland, Fischer, Kirschner & Laemmli (1977) J. Biol. Chem. 252, 1102-1106] with Staphylococcus proteinase, it was found that one group always contained fast myosin heavy chain, whereas the second group always contained the slow form. Moreover, a relatively fast-migrating alpha-tropomyosin was associated with the fast myosin group and a slow-migrating form with the slow myosin group. All fibres also contained beta-tropomyosin; the coexistence of alpha- and beta-tropomyosin is at variance with evidence that alpha-tropomyosin is restricted to fast fibres [Dhoot & Perry (1979) Nature (London) 278, 714-718]. Fast fibres containing the expected fast light chains and troponins I and C fast were identified in the three ra muscles, but in only four sm muscles. In three other sm muscles, all the fast fibres contained two troponins I and an additional myosin light chain that was more typical of myosin light chain 1 slow. The remaining sm muscle contained a fast fibre type that was similar to the first type, except that its myosin light chain 1 was more typical of the slow polymorph. Troponin T was bimorphic in all fast fibres from a ra muscles and in at least some fast fibres from one sm muscle. Peptide 'mapping' revealed two forms of fast myosin heavy chain distributed among fast fibres. Each form was associated with certain other proteins. Slow myosin heavy chain was unvarying in three slow fibre types identified. Troponin I polymorphs were the principal indicator of slow fibre types. The myofibrillar polymorphs identified presumably contribute to contraction properties, but beyond cud chewing involving ma muscle, nothing is known of the conditions that gave rise to the variable fibre composites in sm and ra muscles. 相似文献
14.
V Deveaux I Cassar-Malek B Picard 《Comparative biochemistry and physiology. Part A, Molecular & integrative physiology》2001,131(1):21-29
The aim of the present study was to precise the origin of the particular muscle characteristics of double-muscled cattle by comparing muscle properties of Holstein and double-muscled Belgian Blue (BB) foetuses. Ten 100-day-old foetuses of each genotype were studied. The weight and length of foetuses and the length, weight and area of the Semitendinosus (ST) muscle were analysed. Contractile differentiation of the different fibre types was studied by immunohistochemistry using several monoclonal antibodies raised against different myosin heavy chain isoforms (MHC slow, fast, foetal) and by electrophoresis. Proliferation phase of myoblasts from each genotype was analysed in primary culture. On 100 days of foetal life, the foetuses of both genotypes did not show any significant differences in their weight and length. However, BB cattle already present muscle hypertrophy, which seems to originate from a higher myoblast proliferation observed in primary culture. The use of anti-MHC antibodies shows that ST muscle of BB contained a smaller proportion of primary fibres and a higher proportion of secondary fibres which will give principally fast fibres in adult muscle. Electrophoresis analysis confirms a lower proportion of slow MHC in ST of BB. 相似文献
15.
Orietta Chiara Valeria Danilo Paolo Roberto 《Journal of electromyography and kinesiology》2009,19(5):e290-e300
The aim of the present study was to clarify the impact of long term (1 year) resistance training (RT) on structure and function of single muscle fibres of vastus lateralis in young female subjects. Five young women (age: 25.4 ± 6.2 year) performed exercise sessions at 60% of single subject own repetition maximum (1 RM) 1 h twice a week. Maximum voluntary force was determined pre- and post-RT and was found to significantly increase post-RT ensuring a successful impact of RT on muscle performance in vivo. Needle muscle biopsy samples were obtained both pre- and post-RT and the following determinations were performed: myosin heavy chain isoform (MHC) distribution of the whole muscle samples by SDS–PAGE; cross sectional area (CSA), specific force (Po/CSA) and maximum shortening velocity (Vo) of a large population (n = 358) of single skinned muscle fibres classified on the basis of MHC isoform composition by SDS–PAGE. The results suggest that the long duration of RT can determine a significant increase in specific force (Po/CSA) and unloaded shortening velocity (Vo) of single muscle fibres in female subjects, whereas no muscle fibre hypertrophy and no shift in MHC isoform content was observed. 相似文献
16.
A fluorescently labelled derivative of the calcium binding subunit of troponin, TnC, has been injected into isolated striated muscle fibres from the barnacle Balanus nubilus. The Ca2+ affinity of isolated TnC is close to that of intact troponin when located in the thin filament. Excitation of the TnCDANZ within the muscle cell (325nm) revealed a marked fluorescence at 510 nm and was similar to that observed in vitro, which was absent at 400 or 600 nm after subtraction of the fibre autofluorescence. High Ca2+ salines increased the fluorescence at 510 nm by roughly 2 times. Single voltage clamp pulses produced a rapid rise in fluorescence at 510 nm after allowing for any non-specific changes at 400 nm, and this signal preceded force development by approx. 55 ms at 22 degrees C. It reached a maximum at the same time as force and subsequently decayed more slowly. The fluorescence signal increased in magnitude with increase in stimulus intensity. These results suggest that Ca2+ attaches rapidly to the contractile filament, but is lost relatively slowly and imply a slow decay of the activation process. 相似文献
17.
34 Andalusian foals of both sexes were divided into three age-groups (A = mean age 1 month, B = 7 months, C = 14 months). Samples of the right m. gluteus medius were stained for m-ATPase and NADH-TR in order to determine fibre type composition and size as well as the relative area occupied by each type. Results revealed no statistically significant variation in the proportion of type I fibre among the three age-groups. Significant differences were recorded, however, for type II fibres; an increase in the proportion of IIA fibres was accompanied by a decrease in IIB ones, the difference being most marked between groups A and B. IIB high-oxidative fibres also decreased, while IIB low-oxidative ones showed no significant variation. All fibre types increased significantly in size; types I and IIA recorded a threefold increase, whereas type IIB showed least growth. The relative area occupied by each type increased significantly between groups A and B, but only IIA fibres recorded a significant increase in relative area between groups B and C. 相似文献
18.
Gary C Sieck Wen-Zhi Zhan Young-Soo Han Y S Prakash 《Journal of applied physiology》2007,103(3):858-866
Denervation (DNV) of rat diaphragm muscle (DIAm) decreases myosin heavy chain (MHC) content in fibers expressing MHC(2X) isoform but not in fibers expressing MHC(slow) and MHC(2A). Since MHC is the site of ATP hydrolysis during muscle contraction, we hypothesized that ATP consumption rate during maximum isometric activation (ATP(iso)) is reduced following unilateral DIAm DNV and that this effect is most pronounced in fibers expressing MHC(2X). In single-type-identified, permeabilized DIAm fibers, ATP(iso) was measured using NADH-linked fluorometry. The maximum velocity of the actomyosin ATPase reaction (V(max) ATPase) was determined using quantitative histochemistry. The effect of DNV on maximum unloaded shortening velocity (V(o)) and cross-bridge cycling rate [estimated from the rate constant for force redevelopment (k(TR)) following quick release and restretch] was also examined. Two weeks after DNV, ATP(iso) was significantly reduced in fibers expressing MHC(2X), but unaffected in fibers expressing MHC(slow) and MHC(2A). This effect of DNV on fibers expressing MHC(2X) persisted even after normalization for DNV-induced reduction in MHC content. With DNV, V(o) and k(TR) were slowed in fibers expressing MHC(2X), consistent with the effect on ATP(iso). The difference between V(max) ATPase and ATP(iso) reflects reserve capacity for ATP consumption, which was reduced across all fibers following DNV; however, this effect was most pronounced in fibers expressing MHC(2X). DNV-induced reductions in ATP(iso) and V(max) ATPase of fibers expressing MHC(2X) reflect the underlying decrease in MHC content, while reduction in ATP(iso) also reflects a slowing of cross-bridge cycling rate. 相似文献
19.
Electrophoretic analysis in the presence of 33% glycerol of purified myosin from normal human muscle shows three distinct protein bands which are identified as type 1, 2B, and 2A myosin heavy chain (MHC) isoforms by affinity-purified polyclonal antibodies. Analysis of MHC of single human muscle fibres shows that human muscles contain a large population of fibres showing the coexistence of type 2A and 2B MHC. 相似文献
20.
Changes in fibre diameters of extraocular muscles of the rabbit were studied at different times after denervation. The whole inferior oblique muscle hypertrophied, while some of the muscle fibres hypertrophied and others showed atrophy, depending on the fibre type. Fibre types have been determined by their histochemical enzyme profile. In the central layer of the muscle the phasic muscle fibres, which are rich in mitochondria, exhibited a transient hypertrophy being maximal 4-5 weeks after denervation and afterwards they atrophied; other phasic muscle fibres, which are poor in mitochondria, atrophied without having shown any sign of hypertrophy. Special, putatively slow tonic muscle fibres, which have low enzyme activities, underwent small long-lasting increases of their diameters. In the superficial layer of extraocular muscle there are two types of extremely thin muscle fibres rich in mitochondira. Both these fibre types hypertrophied to the greatest degree and for a very long time. Comparable changes in fibre diameters as described here for the muscle fibre types of an extraocular muscle are known from special muscle fibres in other vertebrate 相似文献