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PubMed1999

Inhibition of muscle protein synthesis by alcohol is associated with modulation of eIF2B and eIF4E.

The present study examined potential mechanisms for the inhibition of protein synthesis in skeletal muscle after chronic alcohol consumption. Rats were maintained on an alcohol-containing diet for 14 wk; control animals were pair fed. Alcohol-induced myopathy was confirmed by a reduction in lean body mass as well as a decrease in the weight of the gastrocnemius and psoas muscles normalized for tibial length. No alcohol-induced decrease in total RNA content (an estimate of ribosomal RNA) was detected in any muscle examined, suggesting that alcohol reduced translational efficiency but not the capacity for protein synthesis. To identify mechanisms responsible for regulating translational efficiency, we analyzed several eukaryotic initiation factors (eIF). There was no difference in the muscle content of either total eIF2alpha or the amount of eIF2alpha in the phosphorylated form between alcohol-fed and control rats. Similarly, the relative amount of eIF2Bepsilon in muscle was also not different. In contrast, alcohol decreased eIF2B activity in psoas (fast-twitch) but not in soleus or heart (slow-twitch) muscles. Alcohol feeding also dramatically influenced the distribution of eIF4E in the gastrocnemius (fast-twitch) muscle. Compared with control values, muscle from alcohol-fed rats demonstrated 1) an increased binding of the translational repressor 4E-binding protein 1 (4E-BP1) with eIF4E, 2) a decrease in the phosphorylated gamma-form of 4E-BP1, and 3) a decrease in eIF4G associated with eIF4E. In summary, these data suggest that chronic alcohol consumption impairs translation initiation in muscle by altering multiple regulatory sites, including eIF2B activity and eIF4E availability.

Adenosine Triphosphate↗

PubMed1995

Influence of inorganic phosphate and pH on ATP utilization in fast and slow skeletal muscle fibers.

The influence of P(i) and pH was studied on myofibrillar ATP turnover and force development during maximally activated isometric contractions, in skinned single fibers from rabbit soleus and psoas muscle. ATP hydrolysis was coupled to the breakdown of NADH, which was monitored photometrically at 340 nm. In psoas the depression by phosphate of force is twice that of ATP turnover, but in soleus force and ATP turnover are depressed equally by P(i). Most, but not all, of the ATPase and force values observed for a combination of high P(i) and low pH could be explained by independent effects of P(i) and pH. The effects of P(i) and pH on ATP turnover can be understood by a three-state cross-bridge scheme. Mass action of phosphate on the reaction from the actomyosin(AM).ADP state to the AM.ADP.P(i) state may largely account for the phosphate dependencies of ATPase activity found. Protons affect cross-bridge detachment from the AM.ADP state and the rate of the AM.ADP.P(i)-to-AM.ADP transition. In this scheme, the effects of P(i) and pH on cross-bridge kinetics appeared to be largely independent.

Actomyosin↗

PubMed1978

[The post mortem alterations of myofibrilar proteins and adenosintriphosphatase activities of the skeletal muscles (author's transl)].

Immediately after the death of rabbits and at different times within 48 hours, we took out a part of the psoas muscle, from which we made myofibrilar preparations. The carcasses providing the muscle samples were held at two different temperatures. One group was held for 48 hours at 25 degrees C, imitating room temperature. The other group was held for 12 hours at 25 C degrees and at 25 C degrees and 12 hours at 10 C degrees, imitating daily temperature changes. Each myofibrilar sample was subjected to SDS-polyacrylamide gel electrophoresis. In addition we determined the Ca++ activated and the EGTA inhibited ATPase specific activity of the myofibrils. We found that within 48 hours the myofibrilar proteins were subjected to some characteristic proteolytic changes, which were dependant on the environmental temperature. The most interesting change was found in carcasses held constantly at 25 C degrees for 48 hours, where the EGTA inhibited ATPase activity was increased to about seven times its initial value, reflecting impairment of the troponin complex.

Actinin↗

PubMed1980

Orientation of spin-labeled myosin heads in glycerinated muscle fibers.

We have used electron paramagnetic resonance (EPR) spectra to study spin labels selectively and rigidly attached to myosin heads in glycerinated rabbit psoas muscle fibers. Because the angle between the magnetic field and the principal axis of the probe determines the position of the EPR absorption line, spectra from labeled fibers oriented parallel to the magnetic field yielded directly the distribution of spin label orientations relative to the fiber axis. Two spin labels, having reactivities resembling iodoacetamide (IASL) and maleimide (MSL), were used. In rigor fibers with complete filament overlap, both labels displayed a narrow angular distribution, full width at half maximum approximately 15 degrees, centered at angles of 68 degrees (IASL) and 82 degrees (MSL). Myosin subfragments (heavy meromyosin and subfragment-1) were labeled and allowed to diffuse into fibers. The resulting spectra showed the same sharp angular distribution that was found for the labeled fibers. Thus is appears that virtually all myosin heads in a rigor fiber have the same orientation relative to the fiber axis, and this orientation is determined by the actomyosin bond. Experiments with stretched fibers indicated that the spin labels on the fraction of heads not interacting with actin filaments had a broad angular distribution. Addition of ATP to unstretched fibers under relaxing conditions produced orientational disorder, resulting in a spectrum almost indistinguishable from that of an isotropic distribution of probes. Addition of either an ATP analog (AMPPNP) or pyrophosphate produced partial disorder. That is a fraction of the probes remained sharply oriented as in rigor while a second fraction was in a disordered distribution similar to that of relaxed fibers.

Actins↗

PubMed1985

The inhibition of muscle contraction by adenosine 5' (beta, gamma-imido) triphosphate and by pyrophosphate.

We have studied the inhibition of the contraction of glycerinated rabbit psoas muscle caused by ligands that bind to the ATPase site of myosin. Two ligands, adenosine 5' (beta, gamma-imido) triphosphate (AMPPNP) and pyrophosphate (PPi), decreased the force and stiffness developed in isometric contractions and the velocity of shortening of isotonic contractions. The force exerted by isometric fibers was measured as a function of MgATP in the presence and absence of a constant concentration of the ligands. As the MgATP concentration decreased, the inhibition of tension caused by the ligand increased, reaching approximately 50% at 25 microM MgATP and either 2 mM MgPPi or 2 mM MgAMPPNP. The maximum velocity of shortening was also measured as a function of MgATP concentration in the presence of 1 and 2 mM MgPPi and 2.5 and 5 mM MgAMPPNP. Both ligands acted as pure competitive inhibitors with Ki = 3.0 mM for PPi and 5.1 mM for MgAMPPNP. These data show that both ligands are weak inhibitors of the contraction of fibers. The results provided information on the energetics of actin-myosin-ligand states that occur in the portion of the cross-bridge cycle where MgATP binds to myosin. A simple analysis of the inhibition of velocity suggests that MgAMPPNP binds to the actomyosin complex at this step of the cycle with an effective affinity constant of approximately 2 X 10(2) M-1.

Adenosine Triphosphate↗

PubMed1988

Effects of AMPPNP on the orientation and rotational dynamics of spin-labeled muscle cross-bridges.

We have used electron paramagnetic resonance (EPR) to investigate the orientation, rotational motion, and actin-binding properties of rabbit psoas muscle cross-bridges in the presence of the nonhydrolyzable nucleotide analogue, 5'-adenylylimido-diphosphate (AMPPNP). This analogue is known to decrease muscle tension without affecting its stiffness, suggesting an attached cross-bridge state different from rigor. We spin-labeled the SH1 groups on myosin heads and performed conventional EPR to obtain high-resolution information about the orientational distribution, and saturation transfer EPR to measure microsecond rotational motion. At 4 degrees C and 100 mM ionic strength, we find that AMPPNP increases both the orientational disorder and the microsecond rotational motion of myosin heads. However, computer analysis of digitized spectra shows that no new population of probes is observed that does not match either rigor or relaxation in both orientation and motion. At 4 degrees C, under nearly saturating conditions of 16 mM AMPPNP (Kd = 3.0 mM, determined from competition between AMPPNP and an ADP spin label), 47.5 +/- 2.5% of myosin heads are dynamically disoriented (as in relaxation) without a significant decrease in rigor stiffness, whereas the remainder are rigidly oriented as in rigor. The oriented heads correspond to actin-attached heads in a ternary complex, and the disoriented heads correspond to detached heads, as indicated by EPR experiments with spin-labeled subfragment 1 (S1) that provide independent measurements of orientation and binding. We take these findings as evidence for a single-headed cross-bridge that is as stiff as the double-headed rigor cross-bridge. The data are consistent with a model in which, in the presence of saturating AMPPNP, one head of each cross-bridge binds actin about 10 times more weakly, whereas the remaining head binds at least 10 times more strongly, than extrinsic S1. Thus, although there is no evidence for heads being attached at nonrigor angles, the attached cross-bridge differs from that of rigor. The heterogeneous behavior of heads is probably due to steric effects of the filament lattice.

Actins↗

PubMed2004

Kinetics of muscle contraction and actomyosin NTP hydrolysis from rabbit using a series of metal-nucleotide substrates.

Mechanical properties of skinned single fibres from rabbit psoas muscle have been correlated with biochemical steps in the cross-bridge cycle using a series of metal-nucleotide (Me.NTP) substrates (Mn(2+) or Ni(2+) substituted for Mg(2+); CTP or ITP for ATP) and inorganic phosphate. Measurements were made of the rate of force redevelopment following (1) slack tests in which force recovery followed a period of unloaded shortening, or (2) ramp shortening at low load terminated by a rapid restretch. The form and rate of force recovery were described as the sum of two exponential functions. Actomyosin-Subfragment 1 (acto-S1) Me.NTPase activity and Me.NDP release were monitored under the same conditions as the fibre experiments. Mn.ATP and Mg.CTP both supported contraction well and maintained good striation order. Relative to Mg.ATP, they increased the rates and Me.NTPase activity of cross-linked acto-S1 and the fast component of a double-exponential fit to force recovery by approximately 50% and 10-35%, respectively, while shortening velocity was moderately reduced (by 20-30%). Phosphate also increased the rate of the fast component of force recovery. In contrast to Mn(2+) and CTP, Ni.ATP and Mg.ITP did not support contraction well and caused striations to become disordered. The rates of force recovery and Me.NTPase activity were less than for Mg.ATP (by 40-80% and 50-85%, respectively), while shortening velocity was greatly reduced (by approximately 80%). Dissociation of ADP from acto-S1 was little affected by Ni(2+), suggesting that Ni.ADP dissociation does not account for the large reduction in shortening velocity. The different effects of Ni(2+) and Mn(2+) were also observed during brief activations elicited by photolytic release of ATP. These results confirm that at least one rate-limiting step is shared by acto-S1 ATPase activity and force development. Our results are consistent with a dual rate-limitation model in which the rate of force recovery is limited by both NTP cleavage and phosphate release, with their relative contributions and apparent rate constants influenced by an intervening rapid force-generating transition.

Actomyosin↗

PubMed1985

The effect of myosin phosphorylation on the contractile properties of skinned rabbit skeletal muscle fibers.

We have studied the effect of myosin P-light chain phosphorylation on the isometric tension generated by skinned fibers from rabbit psoas muscle at 0.6 and 10 microM Ca2+. At the lower Ca2+ concentration, which produced 10-20% of the maximal isometric tension obtained at 10 microM Ca2+, addition of purified myosin light chain resulted in a 50% increase in isometric tension which correlated with an increase in P-light chain phosphorylation from 0.10 to 0.80 mol of phosphate/mol of P-light chain. Addition of a phosphoprotein phosphatase reversed the isometric tension response and dephosphorylated P-light chain. At the higher Ca2+ concentration, P-light chain phosphorylation was found to have little effect on isometric tension. Fibers prepared and stored at -20 degrees C in a buffer containing MgATP, KF, and potassium phosphate incorporated 0.80 mol of phosphate/mol of P-light chain. Addition of phosphoprotein phosphatase to these fibers incubated at 0.6 microM Ca2+ caused a reduction in isometric tension and dephosphorylation of the P-light chain. There was no difference before and after phosphorylation of P-light chain in the normalized force-velocity relationship for fibers at the lower Ca2+ concentration, and the extrapolated maximum shortening velocity was 2.2 fiber lengths/s. Our results suggest that in vertebrate skeletal muscle, P-light chain phosphorylation increases the force level at submaximal Ca2+ concentrations, probably by affecting the interaction between the myosin cross-bridge and the thin filament.

Animals↗

PubMed1978

Anatomical analysis of the developmental effects of aneuploidy in man--the 18-trisomy syndrome: II. Anomalies of the upper and lower limbs.

We report the anatomical variations of the limbs in eight infants with the trisomy-18 syndrome that were dissected and studied in detail. In each case, the upper limbs showed defects which further define the specific influence of this aneuploidy on the development of its preaxial (radial) component, and the tendency towards reduction defects. Abnormalities included muscle variations concentrated along the radial margin of the forearm and hand, the absence of the definitive musculocutaneous nerve in all of the limbs, and reductions of the radial artery in four of the bodies. Pathogenetic mechanisms explaining the observed defects are discussed, and include: 1) a defect in peripheral nerve development; or 2) tissue necrosis. The characteristic flexion deformities of the fingers seem to be due to a displacement of the tendons of extensors digitorum and digiti minimi. The lower limbs did not show a consistent pattern of defects, except for the absence of some muscles (psoas minor, the tendon of flexor digitorum brevis to digit V), and the presence of several supernumerary muscles. These variations are discussed as possible nonspecific effects of 18-trisomy on development. The additional anatomical data from this and the first paper in this series [Bersu and Ramirez-Castro, 1977] provide a more detailed picture of the trisomy-18 phenotype which may be useful in corroborating an unconfirmed clinical diagnosis of the syndrome.

Abnormalities, Multiple↗

PubMed2003

Musculoskeletal dysfunction in men with chronic pelvic pain syndrome type III: a case-control study.

PURPOSE: Men with chronic pelvic pain syndrome (CPPS) type III experience pelvic pain of uncertain etiology. Pain has been attributed to prostatic, bladder and muscular origins. Few studies have documented pelvic and abdominal muscle function in men with CPPS or compared their muscular examination to that of men without pain. We hypothesized that the musculoskeletal examinations of men with CPPS types IIIA and IIIB would show more spasm, tenderness and dysfunction than in men without CPPS. MATERIALS AND METHODS: A total of 62 men with CPPS and 89 healthy men without pelvic pain underwent a standardized musculoskeletal examination by a licensed physical therapist. RESULTS: Controls and patients with pain showed a significant difference in muscle spasm, increased muscle tone, pain with internal transrectal palpation of the pelvic muscles, and increased tension and pain with palpation of the levator ani and coccygeus muscles (p <0.001). Patients with pain also had significantly greater pain and tension with palpation of the psoas muscles and groin. Patients and controls did not differ significantly in strength testing of the lower abdominal and oblique muscles. CONCLUSIONS: Men with CPPS have more abnormal pelvic floor muscular findings compared with a group of men without pain. Abnormalities of the pelvic muscles may contribute to this pain syndrome.

Abdominal Muscles↗

PubMed1978

Radiologic soft tissue shadows in the pelvis: another look.

In patients with adequate amounts of intramuscular fat, the normal contours of the muscles of the pelvic floor and side-walls may be visualized on plain radiographs. Knowledge of the relationships of these muscles to surrounding structures has been facilitated by computed tomography. Obliteration of the medial margin of the psoas muscle with an attendant soft tissue mass implies pathology in the region of the medial chain of external iliac lymph nodes; similarly, obliteration of the obturator internus shadow suggests internal iliac adenopathy. Nonnodal masses in these regions can cause similar radiographic abnormalities. The normal shadow of the piriformis muscle may simulate external iliac adenopathy. Pitfalls which may lead to overinterpretation are discussed.

Adipose Tissue↗

PubMedDate not supplied

The state of preservation of the cadaver of the Marquise of Tai found in the Han Tomb No. 1 in Mawangtui near Changsha as revealed by the fine structure of the muscle and other tissues.

The cadaver in the Han Tomb No. 1 at Mawangtui near Changsha, Human Province, excavated during the Great Proletarian Cultural Revolution and the movement to criticize Lin Piao and Confucius, is the remains of the wife of Litsang, the Marquis of Tai, the Chancellor of the principality of Changsha in the early Western Han Dynasty. The cadaver, buried underground for more than 2,100 years, is very well-preserved. The results presented in this paper are a part of the multidisciplinary investigations of the state of preservation of the cadaver, which, together with the studies of the pathological changes and the cause of death, and the attempts at unveiling the secret of preservation, constituted the main objectives of the coordinated research activities for the Han cadaver. This paper describes the fine structure of the muscle and other tissues of the cadaver. By an extensive analysis of the electron micrographs of the psoas muscle, by fractionation of various fragments of the same, and by simulation experiments with fresh human muscle incubated with cathepsins, it is possible to show that the muscle fibril assumes the shape of a bamboo shoot and is made up of a stack of alternate layers of two "half A disks" (one wing of the A cylinder minus the H zone) to one Z disk, held together by remnants of the microfilaments and wrapped up in the sarcoplasmic reticulum. The H zone of the A band and the I filaments have preferentially autolyzed. The best preserved portions of the Han muscle still retain antigenicity to a certain extent. The best-preserved of all proteins is collagen, retaining much of the macromolecular, chemical and biochemical characteristics, whereas pancreatic enzymes, cytochrome C and other stable proteins could no longer be detected. The separation of degradative processes into endogenous autolysis and exogenous putrefaction, the synthesis of the factor of macromolecular stability and the factor of autolytic environment, and the disentanglement of the changes occurring soon after death and the long-term gradual changes, have been discussed in an attempt to understand how the corpse changed in the course of time and why it was so well-preserved. The well-preservedness of the cadaver of the Marquise of Tai once again testifies to the creative wisdom of the labouring class of our ancestors.

Cathepsins↗

PubMed1985

Disassembly from both ends of thick filaments in rabbit skeletal muscle fibers. An optical diffraction study.

We show in this paper that the change of the internal structure of a sarcomere in a rabbit glycerinated psoas muscle fiber can be examined by analyzing the intensity change of the first- and the second-order optical diffraction lines. A unit-cell (sarcomere)-structure model has been applied to the estimation of the length of thick filaments in a muscle fiber while they undergo dissociation. The optical factors, except for the unit-cell-structure factor, hardly changed during the dissociation of the filaments. Our results show that thick filaments dissociate from both ends on increasing the KCl concentration in the presence of 10 mM pyrophosphate and 5 mM MgCl2. Micromolar concentrations of Ca2+ suppressed to some extent the dissociation of thick filaments. The disassembly of thick filaments occurred at higher KCl concentrations in the absence of pyrophosphate. There was a correlation between the stability of the thick filament structure and cross-bridge formation, which was induced either by the addition of micromolar concentrations of Ca2+ in the presence of Mg-pyrophosphate or by removal of Mg-pyrophosphate.

Animals↗

PubMed1980

Binding of heavy meromyosin and subfragment-1 to thin filaments in myofibrils and single muscle fibers.

The binding of fluorescently labeled heavy meromyosin (HMM) and heavy meromyosin subfragment-1 (S-1) to thin filaments of myofibrils and of rabbit psoas muscle fibers was measured under conditions of rigor and contraction. The fragments diffused rapidly into the myofibrillar space and bound specifically to the thin filaments. The fragments bound strongest and in a uniform fashion to myofibrils in which the competition from indigenous myosin was abolished by removing it with Hasselbach-Schneider solution. Under these conditions, the rigor Ka values for HMM and S-1 were 1.5 x 10(6) M-1 and 4.8 x 10(4) M-1, respectively. The stoichiometry of binding was measured by independently estimating the concentration of actin sites. S-1 was found to be capable of saturating all available actin sites in a myofibril or a fiber, but HMM could only occupy 50% of the sites.

Actins↗

PubMedDate not supplied

[Interaction of vanadate with the contractile system of striated muscles in the presence of natural analogs of ATP and ADP].

Vanadate produced dissociation of rigor-activated (calcium-free) fibres or rabbit m. psoas muscle in the presence of the studied various natural analogs of ATP (NTP) at optimal concentrations. By the degree of sensitivity to vanadate it is possible to establish the order ATP approximately greater than CTP greater than UTP greater than ITP greater than GTP. This series corresponds to the order for actomyosin NTPases qualitatively. Addition of corresponding NDP to fibres produced a decrease of the rigor fibres tension. Vanadate in comparable concentrations does not change the mechanical properties of fibres in the presence of NDP. At high concentration (greater than 10 mM) vanadate produced relaxation of the rigor fibres even in the absence of nucleotides. This effect is irreversible.

Adenosine Diphosphate↗

PubMed1980

Retroperitoneal processes involving the psoas demonstrated by computed tomography.

Twenty-five patients were found to have retroperitoneal pathology involving the psoas muscle including nine patients with inflammatory lesions, three with hematomas, seven with adenopathy, one patient with leukemic infiltration of the psoas, and five with retroperitoneal tumors. Computed tomography (CT) offers a unique method to investigate pathological processes that affect the psoas. In addition, the abdominal films on 24 of the patients were analyzed to correlate the value of radiography with that of CT. Computed tomography confirms the belief that the mere presence of a retroperitoneal mass will not necessarily obliterate the psoas.

Abscess↗

PubMed1985

Shortening velocity and myosin heavy chains of developing rabbit muscle fibers.

The regulation of vertebrate muscle contraction with respect to the role of the different subunits of myosin remains somewhat uncertain. One approach to gaining a better understanding of the molecular basis of contraction is to study developing muscle which undergoes changes in myosin isozyme composition and contractile properties during the normal course of maturation. The present study utilizes single fibers from psoas muscles of rabbits at several ages as a model system for fast-twitch muscle development. This approach eliminates the inherent problems of interpreting results from studies on whole muscles which usually contain heterogeneous fiber types with respect to contractile properties and isoenzyme composition. Maximum velocity of shortening and tension-generating ability of individual fibers were measured and the myosin heavy chain composition of the same fibers was examined using an ultrasensitive sodium dodecyl sulfate-polyacrylamide gel system. The results indicate that 1) with regard to contractile properties, there is a transitional period from slow to fast shortening velocities within the first postnatal month; 2) a strong, positive correlation exists between the speed of shortening and tension-generating ability of individual postnatal day 7 fibers, suggesting that as more myosin is incorporated in these developing fibers it is of the fast type; and 3) there is a wide variation in maximum velocity of shortening among postnatal day 7 psoas fibers which is also a time when a mixture of heavy chain isoforms characterizes the myosin composition of single muscle fibers.

Aging↗

PubMed1987

The positional stability of thick filaments in activated skeletal muscle depends on sarcomere length: evidence for the role of titin filaments.

Electron microscopy was used to study the positional stability of thick filaments in isometrically contracting skinned rabbit psoas muscle as a function of sarcomere length at 7 degrees C. After calcium activation at a sarcomere length of 2.6 micron, where resting stiffness is low, sarcomeres become nonuniform in length. The dispersion in sarcomere length is complete by the time maximum tension is reached. A-bands generally move from their central position and continue moving toward one of the Z-discs after tension has reached a plateau at its maximum level. The lengths of the thick and thin filaments remain constant during this movement. The extent of A-band movement during contraction depends on the final length of the individual sarcomere. After prolonged activation, all sarcomeres between 1.9 and 2.5 micron long exhibit A-bands that are adjacent to a Z-disc, with no intervening I-band. Sarcomeres 2.6 or 2.7 micron long exhibit a partial movement of A-bands. At longer sarcomere lengths, where the resting stiffness exceeds the slope of the active tension-length relation, the A-bands remain perfectly centered during contraction. Sarcomere symmetry and length uniformity are restored upon relaxation. These results indicate that the central position of the thick filaments in the resting sarcomere becomes unstable upon activation. In addition, they provide evidence that the elastic titin filaments, which join thick filaments to Z-discs, produce almost all of the resting tension in skinned rabbit psoas fibers and act to resist the movement of thick filaments away from the center of the sarcomere during contraction.

Actin Cytoskeleton↗