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D Pette

Publications and source records attributed to D Pette.

At least 91 records · Page 5Linked to original sources
PubMed1996

Coordinate changes of myosin light and heavy chain isoforms during forced fiber type transitions in rabbit muscle.

Skeletal muscle fibers are versatile entities, capable of changing their phenotype in response to altered functional demands. In the present study, fast-to-slow fiber type transitions were induced in rabbit tibialis anterior (fA) muscles by chronic low-frequency stimulation (CLFS). The time course of changes in relative protein concentrations of fast and slow myosin light chain (MLC) isoforms and changes in their relative synthesis rates by in vivo labeling with [35S]methionine were followed during stimulation periods of up to 60 days. Generally, relative synthesis rates and protein concentrations changed in parallel; i.e., fast isoforms decreased and slow isoforms increased. MLC3f, however, which turns over at a higher rate than the other light chains, exhibited a conspicuous discrepancy between a markedly reduced relative synthesis but only a moderate decrease in protein amount during the initial 2 weeks of CLFS. Apparently, MLC3f is regulated independent of MLC1f, with protein degradation playing an important role in its regulation. The exchange of fast MLC isoforms with their slow counterparts seemed to correspond to the ultimate fast-to-slow (MHCIIa-->MHCI) transition at the MHC level. However, due to an earlier onset of the fast-to-slow transition of the regulatory light chain and the delayed fast-to-slow exchange of the alkali light chains, a spectrum of hybrid isomyosins composed of fast and slow light and heavy chains must have existed transiently in transforming fibers. Such hybrid isomyosins appeared to be restricted to MHCIIa- and MHCI-based combinations. In conclusion, fiber type specific programs that normally coordinate the expression of myofibrillar protein isoforms seem to be maintained during fiber type transitions. Possible differences in post-transcriptional regulation may result in the transient accumulation of atypical combinations of fast and slow MLC and MHC isoforms, giving rise to the appearance of hybrid fibers under the conditions of forced fiber type conversion.

Adaptation, Physiological↗
PubMed1996

Fiber transformation and replacement in low-frequency stimulated rabbit fast-twitch muscles.

The fast-to-slow conversion of rabbit skeletal muscles by chronic low-frequency (10 Hz, 12 h daily) stimulation involves (1) sequential fast-to-slow fiber-type transitions in the order of type IID-->type IIA-->type I, and (2) the replacement of deteriorating fast-twitch glycolytic fibers by new fibers derived from satellite cells and myotubes. These two processes were analyzed in 30- and 60-day stimulated extensor digitorum longus and tibialis anterior muscles. Fast-to-slow transforming fibers were identified by myofibrillar actomyosin histochemistry as type C fibers and immunohistochemically by their reaction with monoclonal antibodies specific to slow and fast myosin heavy chain isoforms. In situ hybridization of mRNA specific to the myosin heavy chain I isoform identified all fibers expressing slow myosin, i.e., type I and C fibers. The fraction of transforming fibers ranged between 35% and 50% in 30-day stimulated muscles. The percentage of type I fibers (20%) was threefold elevated in extensor digitorum longus muscle, but unaltered (3.5%) in tibialis anterior muscle, suggesting that fast-to-slow fiber conversion was more advanced in the former than in the latter. Fiber replacement was indicated by the finding that the fiber populations of both muscles contained 15% myotubes or small fibers with central nuclei. In situ hybridization revealed that myotubes and small regenerating fibers uniformly expressed myosin heavy chain I mRNA. Similarly, high percentages of slow-myosin-expressing myotubes and small fibers were found in 60-day stimulated muscles.

Adenosine Triphosphatases↗
PubMed1996

Abnormal myotonic dystrophy protein kinase levels produce only mild myopathy in mice.

Myotonic dystrophy (DM) is commonly associated with CTG repeat expansions within the gene for DM-protein kinase (DMPK). The effect of altered expression levels of DMPK, which is ubiquitously expressed in all muscle cell lineages during development, was examined by disrupting the endogenous Dmpk gene and overexpressing a normal human DMPK transgene in mice. Nullizygous (-/-) mice showed only inconsistent and minor size changes in head and neck muscle fibres at older age, animals with the highest DMPK transgene expression showed hypertrophic cardiomyopathy and enhanced neonatal mortality. However, both models lack other frequent DM symptoms including the fibre-type dependent atrophy, myotonia, cataract and male-infertility. These results strengthen the contention that simple loss- or gain-of-expression of DMPK is not the only crucial requirement for development of the disease.

Animals↗
PubMed1995

Effects of low-frequency stimulation on soluble and structure-bound activities of hexokinase and phosphofructokinase in rat fast-twitch muscle.

Several glycolytic enzymes exist in muscle as free and structure-bound forms. A fraction of hexokinase (HK) is associated with the outer mitochondrial membrane. Phosphofructokinase (PFK) and aldolase (ALD) bind to F-actin, and AMP deaminase (AMPase) interacts with myosin. Using low-frequency stimulation (10 Hz, 24 h/d), we studied in rat fast-twitch muscle effects of contractile activity on soluble and structure-bound forms of these enzymes. Phosphoglucose isomerase (PGI), a soluble enzyme, was also examined. Fractional extraction was applied to study the intracellular distribution of soluble and bound enzyme activities 5 min, 1 h, 3 h, 1 d, and 7 d after the onset of stimulation. Confirming previous findings, total HK activity increased 7-fold in 7-d-stimulated muscles, whereas PFK, ALD, and PGI were reduced, ranging between 55% and 80% of their normal activities. AMPase activity was unaltered. At the time points studied, no changes were found in the extraction behavior of PGI and AMPase. The fraction of bound ALD increased slightly (12%). However, the distribution of HK and PFK was markedly altered. Bound PFK increased from 50% in the control to 85% in 7-d-stimulated muscles. Bound HK rose from 52% to 83% during the same time period. The increase in PFK binding was steep and occurred mainly within the first minutes and hours. The increase in HK binding occurred with some delay, but was significant in muscles stimulated for more than 1 h. In view of the altered kinetic properties of F-actin-bound PFK (alleviated allosteric inhibition by ATP) and bound HK (elevated catalytic activity), these changes are interpreted as early responses to match the metabolic demands during maximal contractile activity imposed on a muscle not programmed for sustained activity: Enhanced binding of PFK serves to accelerate glycolytic flux immediately after the onset of stimulation, whereas mitochondrial binding of HK facilitates the phosphorylation of exogenous glucose when glycogen stores have been depleted.

Animals↗
PubMed1995

Reverse transcriptase-polymerase chain reaction detects induction of cardiac-like alpha myosin heavy chain mRNA in low frequency stimulated rabbit fast-twitch muscle.

Using reverse transcriptase-polymerase chain reaction we quantified in rabbit skeletal muscles expression levels of the highly homologous cardiac alpha and beta myosin heavy chain (alpha MHC, beta MHC) mRNA isoforms. Masseter muscle displayed highest levels of a cardiac-like alpha MHC mRNA. This isoform was present at 20-fold lower amounts in slow soleus and at 200-fold lower levels in several fast-twitch muscles. Low-frequency stimulation periods exceeding 20 days drastically induced the alpha MHC mRNA in fast tibialis anterior. The alpha MHC mRNA was 140-fold elevated after 60 days when beta MHC mRNA had increased 50-fold. Our results demonstrate the wide distribution of a cardiac-like alpha MHC mRNA in skeletal muscle and its marked induction during fast-to-slow transition as induced by low-frequency stimulation.

Animals↗
PubMed1995

Patterns of myosin isoforms in mammalian skeletal muscle fibres.

The present article attempts to combine existing information on the distribution of fast and slow myosin isoforms in histochemically distinct muscle fibres. Four myosin heavy chain (MHC) isoforms, MHCI, MHCIIa, MHCIIb, and MHCIId(x), have been identified in small mammals and have been assigned to the histochemically defined fibre types I, IIA, IIB, and IID(X), respectively. These fibres express only one MHC isoform and are called pure fibre types. Hybrid fibres expressing two MHC isoforms are regarded as transitory between respective pure fibre types. The existence of pure and hybrid fibres even in normal muscles under steady state conditions creates a spectrum of fibre types. The multiplicity of fibre types is even greater when myosin light chains are taken into account. A large number of isomyosins results from the combinatorial patterns of various myosin light and heavy chains isoforms, further increasing the diversity of muscle fibres. As shown by comparative studies, the distribution of different fibre types varies in a muscle-specific, as well as a species-specific manner.

Animals↗
PubMed1995

Isomyosin patterns of single type IIB, IID and IIA fibres from rabbit skeletal muscle.

The present study demonstrates for the first time isomyosin patterns of the three fast-twitch fibre types IIB, IID/X, and IIA. Single muscle fibres were dissected from freeze-dried fibre bundles of rabbit adductor magnus, extensor digitorum longus, and psoas muscles. Pure fibre types, expressing only one myosin heavy chain isoform (MHCIIb, MHCIId/x, MHCIIa), were delineated by electrophoresis of fibre fragments under denaturing conditions. Pieces of the same fibres were then subjected to electrophoresis under non-denaturing conditions. A three-band pattern of fast isomyosins, representing the LC3f homodimer (FM1), the LC1f/LC3f heterodimer (FM2), and the LC1f homodimer (FM3), was detected in each of the three pure fibre types. Therefore, three isomyosins, different in their light chain complement, coexist in each pure fibre. The relative mobilities of the three bands, migrating in the order FM1 > FM2 > FM3, were the same in the three fibre types. The absolute electrophoretic mobilities of the MHCIIb-, MHCIId- and MHCIIa-based isomyosin triplets differed in the order MHCIIb triplets > MHCIId triplets > MHCIIa triplets. The proportions of FM1, FM2, and FM3 varied in type IIB, IID, and IIA fibres. FM2 was the dominant isomyosin in all three fibre types, but fibre type-related differences existed in the FM1 to FM3 ratio. This ratio was lowest in IIA fibres and highest in IIB fibres which agrees with our previous observations that the LC3f/(LC1f + LC3f) fraction is lowest in type IIA and highest in type IIB fibres.

Animals↗
PubMed1995

Effects of beta-guanidinopropionic acid-feeding on the patterns of myosin isoforms in rat fast-twitch muscle.

Administration of beta-guanidinopropionic acid (beta-GPA) to rats as 1% of their diet for 6 weeks led to an accumulation of beta-GPA and beta-GPA-phosphate and to a depletion of creatine and phosphocreatine in the fast-twitch plantaris muscle. Adenosine triphosphate concentration was also decreased. Electrophoretic analyses were performed to investigate the effects of beta-GPA on the patterns of fast (FM) and slow (SM) isomyosins, myosin heavy chain (HC) isoforms and myosin light chain (LC) isoforms. The relative concentrations of fast isomyosins FM1 and FM2 decreased, whereas slow isomyosin SM increased. The increase in slow isomyosin corresponded to an increase in the relative concentration of the slow myosin HCI. The changes of the myosin light chain pattern consisted of increases in the relative concentrations of the two slow isoforms, LC1sb and LC2s, and decreases in the fast isoforms LC2f and LC3f. These results demonstrate that beta-GPA administration, leading to a depletion in energy-rich phosphates and a reduced phosphorylation potential, has an impact on myosin isoform expression in rat fast-twitch skeletal muscle.

Adenosine Triphosphate↗
PubMed1995

Dynamic myoplasty in growing dogs as a feasibility study for treatment of fecal incontinence.

The feasibility of skeletal muscle transposition and electrical stimulation (dynamic myoplasty) for treatment of fecal incontinence has been shown in adults. It might be attractive to use such a technique in pediatric patients. Therefore, the influence of growth on skeletal muscle transposition and stimulation was studied in five puppies. In each dog, two neosphincters were constructed around a Thiry-Vella loop by using a dissected sartorius muscle with the neurovascular supply intact. In each of these five puppies, one of these muscles was electrically stimulated during a mean of 19 weeks (one puppy died during the first postoperative week). Muscle biopsies showed an increase in the percentage type I, fatigue-resistant muscle fibers from 61 to 94 in electrically stimulated sartorius neosphincters, but also an increase from 57 to 67 percent in transposed nonstimulated sartorius muscles. The diameter of these type I fibers during growth increased 36% in eletrically stimulated sartorius neosphincters and 55% in nonstimulated sphincters. Function of the neosphincters was tested with the inflow of saline in the Thiry-Vella loop. It was shown that the stimulated neosphincters were capable of inhibiting flow (which corresponded to manometric pressure registrations), but the nonstimulated sphincters were unable to inhibit flow. The experiments were complicated by infection and necrosis around the implanted stimulators in four puppies (which required reimplantation). We conclude that a dynamic myoplasty for fecal incontinence is feasible in growing puppies but that the technique is unacceptable during rapid growth because of the risks of infection and dislocation of the implanted device.

Anal Canal↗
PubMed1994

Stretch activation, unloaded shortening velocity, and myosin heavy chain isoforms of rat skeletal muscle fibres.

1. Contractile properties were investigated on single skinned-fibre preparations from rat leg muscles. Following the mechanical measurements, the myosin heavy chain (HC) composition of the same fibre was analysed by gradient gel electrophoresis. 2. Fibres were typed according to their myosin HC isoform composition (HCI, type I; HCIIA, type IIA; HCIID, type IID; HCIIB, type IIB). Many fibres showed the co-existence of two myosin HC isoforms (hybrid fibres). 3. A strong correlation was found between fibre type and time characteristics of stretch-induced delayed force increase (stretch activation) of fully Ca(2+)-activated fibres. 4. The maximal unloaded shortening velocity (Vmax), as measured with the slack test, was lowest in type I fibres. Within the type II group, a continuum of Vmax values was found, with large overlaps of the different fibre types. 5. The results suggest that the kinetics of stretch activation is determined by the myosin HCs whereas unloaded fibre shortening seems to be determined by other myofibrillar proteins in addition to the myosin HCs. Assuming that stretch activation represents certain steps of the cross-bridge turnover under isometric conditions and Vmax reflects cross-bridge detachment under unloaded conditions it can be deduced that different myofibrillar proteins are responsible for different steps within the cross-bridge turnover.

Animals↗
PubMed1994

Localization of an arginine-specific mono-ADP-ribosyltransferase in skeletal muscle sarcolemma and transverse tubules.

The precise localization of a membrane-bound, arginine-specific mono-ADP-ribosyltransferase (mADP-RT) was assessed in rabbit skeletal muscle by studying membrane fractions isolated by successive sucrose density gradient centrifugations. mADP-RT activity was 10-fold enriched in sarcolemmal and T-tubular membranes. The catalytic activity, determined in preparations with mainly right-side-out vesicles, was found to be on the cytoplasmic face. As revealed by SDS-PAGE and autoradiography endogenous mADP-RT activity labeled several proteins in the range between 15 kDa and 250 kDa. T-tubules contained the highest number of [32P]ADP-ribose-labeled proteins.

ADP Ribose Transferases↗
PubMed1994

Low-frequency stimulation of rat fast-twitch muscle enhances the expression of hexokinase II and both the translocation and expression of glucose transporter 4 (GLUT-4).

This study followed changes in the capacities of uptake and phosphorylation of glucose in response to contractile activity in low-frequency stimulated (10Hz, 24 h/d) rat fast-twitch muscle. We investigated the intracellular distribution of GLUT-4, the major glucose transporter isoform in muscle, changes in the amounts of its specific mRNA and total cellular protein, as well as changes in its relative synthesis rate. These analyses were complemented by measurements of total hexokinase activity and hexokinase II (HKII) expression at the levels of mRNA content and protein synthesis. Changes in protein synthesis were determined by in vivo labeling with [35S]methionine. Translocation of GLUT-4 into the sarcolemma was an immediate response to contractile activity, whereas changes in its total amount were observed only with ongoing stimulation (5 d and longer). A twofold increase in GLUT-4 content after 5 d and longer stimulation periods was preceded by elevations of its mRNA and by enhanced [35S]methionine incorporation. Conversely, increases in HKII expression with a rise in total hexokinase activity occurred soon after the onset of stimulation (30-fold elevations of HKII mRNA after 12 h and 20-fold increases in [35S]methionine incorporation after 24 h). With ongoing stimulation, HKII mRNA and synthesis returned to lower levels (fivefold elevations). Nevertheless, hexokinase activity continued to rise, stabilizing at fivefold-elevated levels after 3 d. These observation suggested that posttranscriptional mechanisms contributed to the upregulation of HKII, e.g. stabilization by elevated intracellular glucose and mitochondrial binding of the enzyme. This suggestion was supported by experiments with cessation after 24 h where hexokinase activity continued to increase, although the mRNA content and, especially, the [35S]methionine incorporation decayed steeply. The increase in HKII prior to GLUT-4 suggests that phosphorylation may be rate limiting in glucose utilization of glycolytic fibers under conditions of sustained contractile activity. Taken together, the changes in distribution and content of GLUT-4, as well as in HKII represent early metabolic adaptations. In addition, they are related to the overall process of stimulation-induced fiber type transformation.

Acetylcholinesterase↗
PubMed1994

Kinetic microphotometric evaluation of in situ hybridization for mRNA of slow myosin heavy chain in type I and C fibres of rabbit muscle.

The present study was undertaken in order to test the possibility of microphotometric evaluation of in situ hybridizations. The histochemical detection of mRNA specific to the slow myosin heavy chain (HCI), in fibre cross sections of normal and transforming rabbit muscles with a digoxigenin-labelled complementary RNA (cRNA) probe was used as a model. Scanning densitometry of Northern blot hybridizations showed that the detection of cRNA/mRNA hybrids by a staining reaction catalysed by alkaline phosphatase coupled to an anti-digoxigenin antibody occurs in a concentration-dependent manner and follows a linear time course. These findings were the basis for elaborating a comparative microphotometric evaluation of in situ hybridization in tissue sections by measuring the reaction rate of the alkaline phosphatase-catalysed formazan production. Relative amounts of HCI mRNA were thus determined by comparing reaction rates instead of by single point microphotometry. This method was applied to studies on the distribution of HCI mRNA in different fibre types of normal rabbit muscles and and muscles undergoing fast-to-slow fibre transformation in response to low-frequency stimulation. The different fibre types were identified by histochemical staining for myofibrillar actomyosin ATPase (mATPase) in cross sections adjacent to the sections processed for in situ hybridization. On the average, type I fibres displayed 2.3-fold higher reaction rates than the mean value recorded for C fibres. According to the pronounced scattering of the values measured in single C fibres, these fibres represented a heterogeneous population in the transforming muscle.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1994

Morphological changes during fiber type transitions in low-frequency-stimulated rat fast-twitch muscle.

This study investigates morphological adaptations of rat extensor digitorum longus muscle to chronic low-frequency stimulation (10 Hz, 10 h/d, up to 61 +/- 7d). During the early stimulation period (2-4 d), increased basophilia and accumulation of RNA were seen predominantly in type-IIB fibers. Putative satellite cell activation, as indicated by 3H-thymidine incorporation, was also evident during this phase. By 12 d, fiber composition remained unaltered, but there was a decrease in the cross-sectional area of the type-IIB fibers. Following 28 d of low-frequency stimulation, the percentage of type-IIB fibers decreased from 43 +/- 3% to 0%, while type-IID fibers increased from 30 +/- 3% to 60 +/- 6%. The fraction of type-IIA fibers tended to increase (controls 19 +/- 3%; stimulated 29 +/- 4%), whereas that of the type-I fibers was unaltered (4 +/- 1%). At this time, the cross-sectional area of type-IID fibers was unaltered, but that of type-IIA and type-I fibers increased. Further stimulation resulted in a return of type-IID fibers to control levels (23 +/- 5%), and a marked increase in type-IIA fibers (45 +/- 8%). The percentage of type-I fibers increased from 4 +/- 1% to 8 +/- 1%. Throughout each stage of chronic stimulation, there was no histological evidence of fiber degeneration and regeneration. These results indicate that, in contrast to the rabbit, chronic low-frequency stimulation-induced fiber conversion in the rat extensor digitorum longus muscle is entirely due to fiber transformation.

Adaptation, Physiological↗
PubMed1994

Role of innervation for development and maintenance of troponin subunit isoform patterns in fast- and slow-twitch muscles of the rabbit.

This study investigates the neural influence on the establishment and maintenance of muscle type-specific expression patterns of the three troponin (Tn) subunits, troponin T (TnT), troponin C (TnC), and troponin I (TnI) during postnatal development and in the adult rabbit. For this purpose, we followed changes in the expression of fast and slow TnT, TnC, and TnI isoforms at the protein and mRNA level in slow- and fast-twitch muscles. During postnatal development all fast Tn isoforms increased in fast-twitch muscle. Sequential transitions (TnTs-->TnT3f-->TnT1f) occurred in the TnT isoform pattern. These changes occurred in parallel with sequential transitions in the pattern of myosin heavy chain (HC) isoforms. Neonatal slow-twitch muscle displayed more mature (slow) isoform patterns for both TnT subunits and myosin HCs than fast-twitch muscle. Although the expression of slow TnC in slow-twitch muscle required innervation, denervation had little effect on slow TnT and TnI which seemed to be controlled by an intrinsic program. In fast-twitch muscle, denervation enhanced the expression of all slow Tn subunit isoforms. In addition, it led to a pronounced increase of the slow TnT2s isoform such that the amount of TnT2s exceeded that of TnT1s. The effects of denervation together with previous data on low-frequency stimulated muscle indicate that the expression of fast Tn isoforms in fast-twitch muscle is neurally controlled. The pattern of slow Tn isoforms in slow-twitch muscle seems to be regulated by an intrinsic program and, in addition, by neural influences.

Animals↗
PubMed1994

Effects of chronic stimulation with different impulse patterns on the expression of myosin isoforms in rat myotube cultures.

In order to study maturation and differentiation of aneural myotubes in vitro, long-term myotube cultures were established from hindlimb musculature of newborn rats. The developmental state of the myotubes was judged by their myosin heavy chain (HC) patterns. Newly formed myotubes only expressed the embryonic isoform, HCemb, older myotubes expressed the neonatal isoform HCneo, as well as the fast adult isoforms HCIIb and HCIId. HCIId increased continuously, reaching a relative concentration of 47% in 37-day-old cultures. The third fast isoform, HCIIa, was not detected and also the slow isoform HCI was absent. Effects of chronic (20 days) electrostimulation were studied by exposing the cultures to various stimulus patterns. Bursts of 250 ms duration at various pulse frequencies were applied at low and high burst frequencies. Although HCemb remained the predominant isoform under all conditions, different stimulus patterns induced specific changes in the patterns of fast and slow HC isoforms. Bursts of 250 ms duration at 15 Hz, 40 Hz, or 100 Hz, repeated every second or every 4 s, induced the expression of slow myosin, i.e., HCl. Bursts of 250 ms duration at 100 Hz, repeated every 100 s, enhanced the expression of HCIId, but not of HCI. Because slow myosin was induced at high burst frequency with low and high pulse rates, we suggest that burst frequency rather than pulse frequency has a specifying effect on myosin expression. Our results show that the basal program of myosin expression during myogenesis in vitro can be modulated by electrostimulation, suggesting a possible influence of neuromuscular activity on the development of adult fiber types.

Animals↗
PubMed1994

Effects of chronic electrical stimulation on myosin heavy chain expression in satellite cell cultures derived from rat muscles of different fiber-type composition.

Myotube cultures were established from satellite cells of three rat muscles of different fiber-type composition, slow-twitch soleus, diaphragm, and fast-twitch tibialis anterior (TA). Effects of chronic electrical stimulation were studied by exposing these cultures for up to 13 days to a stimulus pattern consisting of 250 ms impulse trains of 40 Hz, repeated every 4 s. Changes in myosin expression were assessed at the mRNA level by Northern blotting and in situ hybridization. Expression of slow myosin at the protein level was analysed by immunoblotting and immunohistochemistry with two antibodies, one specific to adult slow myosin, the other reacting with developmental and adult slow myosin heavy chain (MHCI) isoforms. In all three myotube cultures stimulation enhanced the mRNA and protein expression of a developmental isoform of slow myosin (MHCI). However, the three myotube cultures differed in the extent of the increase in MHCI. It was greatest in soleus-derived myotubes, least in TA-derived myotubes, and intermediate in diaphragm-derived myotubes. In addition to the increase in slow myosin, long-term stimulation led to an isoform switch, as indicated by an increase in myotubes reacting with the antibody specific for the adult MHCI. Our results suggest that enhanced contractile activity promotes the expression of the slow phenotype predetermined in satellite cells of slow-twitch, type I fibers. The different extents of increased slow myosin expression may thus be explained as reflecting different percentages of type I fibers and consequently of slow-type satellite cells in the corresponding donor muscles.

Aging↗