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 50,377 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

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 preceded 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.
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PMID:Ontogeny of the pectoralis muscle in the little brown bat, Myotis lucifugus. 803 65

The myocardium is a highly adaptive tissue, as evidenced by phenotypic alterations throughout development and under conditions of altered hemodynamic load. With pressure overload, the myocardium displays adult-to-fetal transitions in expression of contractile and non-contractile proteins. Most intriguing is the fact that many of these transitions are also observed in the senescent heart. The purpose of this work was to establish if the thin filament regulatory proteins, troponin I and troponin T, exhibit reexpression of early developmental isoforms, suggestive of coordinate reprogramming of contractile protein isoform expression. As a functional index of reexpression of the early isoform of troponin I, slow skeletal troponin I, myofibrils were isolated from 12 and 24-month-old Fischer 344 rat ventricles and assayed for myofibrillar ATPase activity at pH 7.0 and 6.5. Both preparations displayed rightward shifts in Ca-ATPase relationships with no differences between groups. SDS-PAGE and Western blot analysis showed that whereas myosin heavy chain expression underwent a transition to predominance of the early development isoform, beta-myosin heavy chain, there was no reexpression of the fetal isoforms of either troponin I or troponin T in the rat heart at 24 months of age. Northern blot analysis using cDNA probes specific for cardiac or slow skeletal troponin I also confirmed the lack of slow skeletal reexpression in the 24-month ventricle. These results are significant in that they demonstrate a lack of coordinate expression of contractile protein isoforms under myocardial adaptation to the aging process.
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PMID:Discoordinate regulation of contractile protein gene expression in the senescent rat myocardium. 807 7

The horse provides an interesting model for study of the structure and function of the mammalian diaphragm. Multiple regions of diaphragm from seven adult horses were prepared for histochemistry, immunocytochemistry, myosin heavy chain electrophoresis, and native myosin electrophoresis. Two additional adults were dissected to demonstrate myofiber and central tendon morphology and stained for acetylcholinesterase to demonstrate motor endplates. All regions of the adult diaphragm were histochemically characterized by a preponderance of type I fibers with some type IIa fibers. Type IIb fibers were absent in all adult specimens. Myosin heavy chain electrophoresis supported the histochemical study: two isoform bands were present on SDS gels that comigrated at the same rate as rat type I and IIa myosin heavy chain isoforms. No isoform was determined to comigrate with rat type IIb heavy chain isoforms. Native myosin isoform analysis revealed two isoforms that comigrated with rat FM-4 and FM-3 (FM = fast myosin) and two isoforms that comigrated with rat SM-1 and SM-2 (SM = slow myosin) isoforms. In some samples, a third slow native myosin isoform was observed that comigrated at the same rate as the SM-3 of the equine biceps brachii muscle. This doublet (or "triplet") of slow isoforms is unique to some horse muscles compared with other adult animals studied. It is not known if these multiple slow native myosin isoforms confer some functional advantage to the equine muscles. The adult equine diaphragm also differs in its morphology by having a large central tendon compared to that in other mammals, and is predominantly slow in fiber type and myosin isoform composition.
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PMID:Morphological, histochemical, and myosin isoform analysis of the diaphragm of adult horses, Equus caballus. 817 13

At least four myosin heavy chain (MHC) isoforms were separated by SDS-PAGE in extracts of intrafusal fibers isolated by microdissection from human lumbrical muscles. The fastest migrating MHC represents a slow isoform. The slowest migrating MHC was identified as the embryonic MHCemb. A faint band, moving slightly faster than MHCemb, most likely represents a neonatal/fetal MHC isoform. A prominent band, moving between the latter and the slow isoform is suggested to represent a hitherto unidentified, spindle-specific MHC isoform, MHCif.
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PMID:Electrophoretically defined myosin heavy chain patterns of single human muscle spindles. 825 4

Six oculorotatory muscles and the levator palpebrae muscle of the rat were analysed by SDS-PAGE for their myosin heavy chain (MHC) isoform patterns. Oculorotatory muscles display a marked predominance of fast MHC isoforms. They contain, in addition to the slow (MHCI) and fast (MHCIIb, MHCIId, MHCIIa) skeletal MHCs, the neonatal MHCneo and the extraocular MHCeom. The levator palpebrae, generally assumed to be a member of the extraocular muscle group because of its innervation by the oculomotor nerve, does not contain MHCneo and MHCeom. It resembles a fast-twitch skeletal muscle with a predominance of MHCIId.
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PMID:Electrophoretic analysis of myosin heavy chain isoform patterns in extraocular muscles of the rat. 825 5

The kinetics of protein metabolism were evaluated in isolated adult feline cardiomyocytes maintained in long term cell culture. The results of these studies suggested that, rather than individual proteins entering a kinetically homogeneous pool, most newly synthesized proteins were segregated into different kinetic compartments with different probabilities of being degraded. Evidence for this conclusion was developed from two types of experiment. The first line of evidence was derived from the kinetics of labeled amino acid incorporation into protein when labeling was conducted over very short or long periods (4 h to 32 days). The observed rates of isotope incorporation over different periods did not fit the expected pattern for a homogeneous pool. A close approximation of observed rates of label incorporation over both short and long labeling intervals could, however, be fit to results predicted using a two-compartment model. When the results of long term equilibration labeling studies were also evaluated relative to short and long term labeling ratios, then it was also possible to identify a unique set of parameters for a two-compartment model which could account for label incorporation in both types of experiment. From this analysis it was estimated that the fast kinetic compartment represented a steady-state level of 10% of total cellular protein with a mean half-life of 21.9 h (ks = 75.9% d-1). The slow kinetic compartment comprised the remaining 90% of protein with a mean t1/2 equal to 15.6 days (ks = 4.4% d-1). Both the observed and predicted equilibration rate of this two compartment mixture was best fit by a single exponential function with an equilibration rate of 5.48% d-1. Based on this outcome, it was also predicted that mixing of nascent and long lived proteins could be followed using a protocol of long and short term labeling in different isotopes followed by a chase period without label. By tracking the isotope ratios in total proteins and SDS-polyacrylamide gel electrophoresis separated proteins, as well as in counts released into the culture medium during the chase period it was determined that nascent proteins were preferentially degraded for a period of at least 48 h following synthesis. Up to 20% of nascent proteins in both the total protein compartment as well as individual proteins, such as myosin heavy chain, were preferentially degraded prior to achieving a state of homogeneous mixing with long lived proteins.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Evidence for post-translational kinetic compartmentation of protein turnover pools in isolated adult cardiac myocytes. 837 85

In smooth muscle tissue, two or three isoforms of myosin heavy chain (MHC) have been reported (SM1, SM2, and/or NM). In mouse uterus tissue, four bands in the region of the MHC's can be resolved on high resolution SDS polyacrylamide gels. Western blots using smooth muscle (SM) MHC-specific and nonmuscle (NM) MHC-specific polyclonal antibodies show the upper two bands in the MHC region are SM isoforms, whereas the lower two bands are NM isoforms. One-dimensional peptide maps of these four bands show each to have a unique pattern of polypeptide fragments following alpha-chymotrypsin digestion. Developmental expression of myosin heavy chains (MHC) in mouse uterus, aorta, bladder, and stomach (6 ages, 10-150 days) was determined using tissue homogenates. In the uterus, both SM MHC's show an increase in relative content with increasing age, whereas the NM MHC's show a decrease. The mouse aorta shows a significant increase in the SM MHC's and a significant decrease in the NM MHC from day 10 to day 30, which is similar to data reported for the rat aorta. Whereas both the bladder and stomach contain relatively small amounts of NM MHC's (approximately 10% or less), these quantities do show decreases with development. The SM1:SM2 ratio for the uterus remains high (3.4 at 150 days) through development; the aorta, bladder, and stomach also start out high, but tend toward 1.0 in the 150-day animals. The presence of four MHC isoforms in the uterus with unique developmental regulation of expression is consistent with hypotheses of unique functional roles for these isoforms.
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PMID:Expression of four myosin heavy chain isoforms with development in mouse uterus. 840 56

Metalloproteinases, myosinase I and myosinase II, that hydrolyze the heavy chain of myosin, were purified from squid mantle muscle. Myosinase I does not hydrolyze other muscle proteins, casein, haemoglobin, or MCA-substrates, while II hydrolyzes tropomyosin. Both myosinase I and myosinase II gave a single protein band on SDS-PAGE with a molecular mass of 16 and 20 kDa, respectively. Their activities were inhibited by EDTA and 1,10-phenanthroline, and II was also inhibited by EGTA. They could be reactivated with some divalent cations, I was especially reactivated with Co2+ and II especially with Zn2+. The optimum pH of both activities was 7.0; the optimum temperature for both was 40 degrees C. Myosinase I hydrolyzes myosin heavy chains to produce 130 and 90 kDa fragments. The N-terminal amino-acid sequence of the 90 kDa fragment indicates that myosinase I splits the myosin heavy chain between Ala-1161 and Thr-1162 in subfragment 2. Myosinase II hydrolyzes myosin heavy chain to produce 158 and 65 kDa fragments, and it splits between Glu-1381 and Thr-1382 in LMM. Myosinases I and II are most likely related to the metabolism of myosin in vivo.
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PMID:Purification and characterization of two metalloproteinases from squid mantle muscle, myosinase I and myosinase II. 842 25

A novel fast-twitch motor unit type, called the IIX-myosin heavy chain (MHC) motor unit, identified by the glycogen depletion technique together with a series of monoclonal antibodies (mAbs) specific for MHCs, has been isolated recently in the rat tibialis anterior muscle. In young animals, this unit has physiological, biochemical and morphometrical properties which separate it from the IIA- and IIB-MHC motor units. In old age, on the other hand, the IIX-MHC units display physiological, biochemical and morphometrical properties resembling the IIB-MHC motor units. Based on these results it was proposed that a transition from IIB to IIX motor units occurs during ageing. In an attempt to clarify this point, the MHC composition was identified by 6% SDS-PAGE and immunoblotting analysis, using specific mAbs antibodies, in the same fast-twitch tibialis anterior muscles in young (3-6 months, n = 9) and old (20-24 months, n = 16) rats from which the single motor units had been identified previously. The IIX-MHC comigrates together with the IIA-MHC band in 6% SDS-PAGE and only two MHC bands are observed in the rat tibialis anterior muscle, i.e. the IIA-IIX- and IIB-MHC bands. A significant increase (P < 0.001) in the average relative amount of the IIA-IIX-MHC was observed in the old (45 +/- 17%) as compared to the young (23 +/- 4%) animals, accompanied by a corresponding decrease in IIB-MHC content. It was demonstrated in immunoblotting analysis that only trace amounts of IIA-MHC were detectable in the IIA-IIX-MHC band in both young and old TA muscles, indicating a substantial increase in the IIX-MHC content in old age. Thus, the present results together with previous observations at the motor unit level strongly support an age-related motor unit transition from type IIB- to IIX-MHC.
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PMID:An age-related type IIB to IIX myosin heavy chain switching in rat skeletal muscle. 847 50

Adult vascular smooth muscle expresses 204-kD (SM1) and 200-kD (SM2) myosin heavy chain (MHC) isoforms. Fetal vascular smooth muscle expresses another 200-kD isoform, MHC-B, that appears to be developmentally regulated. The ontogeny of expression of these MHC isoforms in vascular and nonvascular smooth muscles is not fully understood and may differ. In the present report we examined the ontogeny of these isoforms in aortic and bladder smooth muscle from male fetal (n = 12, 119-140-d gestation; term 145 +/- 5 d) and neonatal (n = 12, 1-33 d) sheep. Tissues were analyzed for total and soluble protein contents. Actin, MHC, and MHC isoforms were analyzed by SDS-PAGE using 3-20% and 4% polyacrylamide gels, respectively. The expression of the adult and fetal 200-kD MHC isoforms were determined by Western analysis. Between 119 d gestation and 33 d neonatal, age-dependent increases (p < 0.02) occurred in bladder actin (16 +/- 0.8 versus 22 +/- 1.4 micrograms/mg of wet weight), MHC (6.5 +/- 0.2 versus 9.7 +/- 1.1) and both soluble (71 +/- 2.9 versus 92 +/- 6.3) and total protein (78 +/- 3.9 versus 103 +/- 5.5). Aortic smooth muscle actin (8.5 +/- 0.7 versus 17 +/- 1.1), MHC (3.1 +/- 0.4 versus 5.2 +/- 0.5), and soluble (44 +/- 2.3 versus 61 +/- 3.0) and total protein (87 +/- 5.8 versus 108 +/- 3.2) also increased (p < 0.01). Aortic SM1 increased (r = 0.79, p < 0.001) during this time, whereas expression of the 200-kD MHC fell (r = -0.79, p < 0.001). In contrast, bladder SM1 fell (r = -0.88, p < 0.001) as the 200-kD MHC rose (r = 0.88, p < 0.001). The type of 200-kD MHC isoform expressed also differed between tissue types; bladder expressed SM2 and little or no MHC-B throughout this phase of development, whereas fetal aorta appeared to express primarily MHC-B, which decreased as adult SM2 expression rose after birth. Expression of smooth muscle proteins and MHC isoforms are developmentally regulated and tissue-dependent, the latter perhaps reflecting developmental differences in organ growth and/or function.
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PMID:Smooth muscle myosin heavy chain isoforms are developmentally regulated in male fetal and neonatal sheep. 855 36


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