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At least 163 records · Page 9Linked to original sources
PubMed1999

Calcium dependence of Donnan potentials in rigor: the effects of [Mg2+] and anions in isolated rabbit psoas muscle fibres.

Contraction in vertebrate striated muscle is known to be dependent upon the binding of calcium ions to the regulatory protein troponin C (TnC). Our electrical (Donnan potential) studies of the subsarcomeric regions have revealed an electrical switching mechanism, which is sensitive to both cation concentration and to particular anions. In a buffer containing phosphate and chloride ions and at 2.7 mM Mg2+ we observe a single charge transition at pCa50 6.8 in both A- and I-bands. At zero Mg2+ the pCa50 of the A-band transition is shifted to 8.0 and the I-band shows two transitions (pCa50 approximately 6.8 and approximately 8.2). Increasing [Mg2+] to 4.5 mM produces a complex effect between pCas 7 and 9 in both bands. All effects are abolished at 9 mM Mg2+. In a chloride-only buffer (imidazole) at zero Mg2+ the direction of the charge transitions is reversed. In addition, two transitions (pCa50 approximately 8.5 and approximately 7.0) are evident in the A-band and three in the I-band (pCa50 approximately 8.5, approximately 7.4, approximately 6.7). In the presence of Mg2+, again the effects of pCa upon the Donnan potential are complex. In the A-band at 2.7 mM Mg2+ two transitions of opposite sign predominate (pCa approximately 7 and approximately 8), whilst in the I band a single transition (pCa approximately 8.3) occurs in the same direction as that observed in phosphate buffer. At 4.5 mM Mg2+ the 'W' shape observed in the corresponding phosphate buffer is preserved in both bands with similar pCa50s. This shape is also apparent in the 9 mM Mg2+ solution. In these two buffer systems, the magnitude of the charge change in terms of electron binding is far larger than expected from simple Ca2+/Mg2+ binding to troponin. In an acetate-only buffer, however, the Donnan potentials of the A-band and I-band were very similar in magnitude and the charge change across the full pCa curve is close to the expected value for Ca2+/Mg2+ binding to troponin. We speculate that titin has a role in the calcium activation of striated muscle in vertebrates for four reasons. First, the effects of long-term storage of the glycerinated muscle; second, the action of [Mg2+]ions; third the effect of anions; and fourth, our published and unpublished observations of sarcomere-length dependence. We also demonstrate the validity of our methodology, relating the charge transitions that we observe to cation-binding studies of a more traditional nature.

Animals↗
PubMed1995

Tension relaxation induced by pulse photolysis of caged ATP in partially crosslinked fibers from rabbit psoas muscle.

Muscle contractile force is thought to be generated by ATP-induced conformational changes in myosin crossbridges. In the present study, we investigated the response to ATP binding of force-bearing, attached cross-bridges. For this investigation, skinned fibers, in which myosin heads were in part covalently crosslinked to thin filaments with a zero-length crosslinker, were prepared. Caged ATP [the P3-1-(2-nitro)phenylethyl ester of ATP] was then pulse-photolyzed in these crosslinked fibers, which retained ATP-induced "rigor" tension, and then the subsequent tension changes were followed at 14-16 degrees C and ionic strengths of 0.1-2 M. A rapid tension decrease was observed after the photolysis in the partially crosslinked fibers. The rate of the decrease was not any different from that in the uncrosslinked fibers compared at ionic strength of 0.2 M. This and other results thus indicate a kinetic similarity in the crosslinked and uncrosslinked crossbridges in response to ATP binding. These findings also suggest that ATP-induced structural changes take place in the attached crossbridges at a rate similar to that of the ATP-induced dissociation of crossbridges from thin filaments.

Actomyosin↗
PubMed1983

[The role of the psoas muscle: apropos of the dissection of the muscles from 10 adults and 10 newborn infants].

The action of the iliopsoas muscle (Musculus iliopsoas) on movements of the hip is studied by direct traction on fresh cadavers (10 still-born and 10 adults). The psoas muscle is a powerful flexor of the hip but also an external rotator. The action of external rotation is moderate but obvious in every position of the femur (Os femoris) and more important if previously in abduction and internal rotation.

Adult↗
PubMedDate not supplied

Tuberculous psoas muscle abscess following chemoprophylaxis with isoniazid in a patient with human immunodeficiency virus infection.

A 34-year-old man with human immunodeficiency virus infection and disseminated Mycobacterium avium and Mycobacterium intracellulare infection developed a right psoas muscle abscess due to Mycobacterium tuberculosis. The abscess occurred 18 months after completion of a 12-month course of chemoprophylaxis with isoniazid that was given because of a positive reaction with purified protein derivative of tuberculin. The adjacent vertebrae did not appear to be involved. The abscess was drained with a percutaneously inserted catheter, and he received standard antituberculous chemotherapy. Three weeks into therapy, a second drainage with a catheter was required. The isolation of two mycobacteria in this patient and the apparent failure of chemoprophylaxis with isoniazid are noted.

Abscess↗
PubMed2001

Temperature dependence of active tension in mammalian (rabbit psoas) muscle fibres: effect of inorganic phosphate.

1. The effect of added inorganic phosphate (P(i), range 3-25 mM) on active tension was examined at a range of temperatures (5-30 degrees C) in chemically skinned (0.5 % Brij) rabbit psoas muscle fibres. Three types of experiments were carried out. 2. In one type of experiment, a muscle fibre was maximally activated at low temperature (5 degrees C) and its tension change was recorded during stepwise heating to high temperature in approximately 60 s. As found in previous studies, the tension increased with temperature and the normalised tension-(reciprocal) temperature relation was sigmoidal, with a half-maximal tension at 8 degrees C. In the presence of 25 mM added P(i), the temperature for half-maximal tension of the normalised curve was approximately 5 degrees C higher than in the control. The difference in the slope was small. 3. In a second type of experiment, the tension increment during a large temperature jump (from 5 to 30 degrees C) was examined during an active contraction. The relative increase of active tension on heating was significantly higher in the presence of 25 mM added P(i) (30/5 degrees C tension ratio of 6-7) than in the control with no added P(i) (tension ratio of approximately 3). 4. In a third type of experiment, the effect on the maximal Ca(2+)-activated tension of different levels of added P(i) (3-25 mM) (and P(i) mop adequate to reduce contaminating P(i) to micromolar levels) was examined at 5, 10, 20 and 30 degrees C. The tension was depressed with increased [P(i)] in a concentration-dependent manner at all temperatures, and the data could be fitted with a hyperbolic relation. The calculated maximal tension depression in excess [P(i)] was approximately 65 % of the control at 5-10 degrees C, in contrast to a maximal depression of 40 % at 20 degrees C and 30 % at 30 degrees C. 5. These experiments indicate that the active tension depression induced by P(i) in psoas fibres is temperature sensitive, the depression becoming less marked at high temperatures. A reduced P(i)-induced tension depression is qualitatively predicted by a simplified actomyosin ATPase cycle where a pre-phosphate release, force-generation step is enhanced by temperature.

Algorithms↗
PubMed1996

Increase in ATP consumption during shortening in skinned fibres from rabbit psoas muscle: effects of inorganic phosphate.

1. The influence of inorganic phosphate (P(i)) on the relationship between ATP consumption and mechanical performance under isometric and dynamic conditions was investigated in chemically skinned single fibres or thin bundles from rabbit psoas muscle. Myofibrillar ATPase activity was measured photometrically by enzymatic coupling of the regeneration of ATP to the oxidation of NADH. NADH absorbance at 340 nm was determined inside a miniature (4 microliters) measuring chamber. 2. ATP consumption due to isovelocity shortenings was measured in the range between 0.0625 and 1 L0 s-1(L0: fibre length previous to shortening, corresponding to a sarcomere length of 2.64 microns), in solutions without added P(i) and with 30 mM P(i). To get an estimate of the amount of ATP utilized during the shortening phase, quick releases of various amplitudes were also performed. 3. After quick releases, sufficiently large that force dropped to zero, extra ATP was hydrolysed which was largely independent of the amplitude of the release and of the period of unloaded shortening. This extra amount, above the isometric ATP turnover, corresponded to about 0.7 and 0.5 ATP molecules per myosin head at 0 and 30 mM P(i), respectively. 4. ATP turnover during the isovelocity shortenings was higher than isometric turnover and increased with increasing shortening velocity up to about 2.7 times the isometric value. At low and moderate velocities of shortening (< 0.5 L0 s-1), P(i) reduced ATP turnover during isovelocity shortening and isometric ATP turnover to a similar extent, i.e. a decrease to about 77% between 0 and 30 mM added P(i). 5. The extra ATP turnover above the isometric value, resulting from isovelocity shortenings studied at different speeds, was proportional to the power output of the preparation, both in the absence and presence of added [P(i)]. 6. The effect of shortening velocity and [P(i)] on energy turnover can be understood in a cross-bridge model that consists of a detached, a non- or low-force-producing, and a force-producing state. In this model, mass action of P(i) influences the equilibrium between the force-producing and the non-or-low-force-producing cross-bridges, and shortening enhances cross-bridge detachment from both attached states.

Adenosine Triphosphatases↗
PubMed1984

[Hydatid cyst of the psoas muscle. Diagnosis using the CT scanner].

A 30-year-old Maroccan man was admitted with a swelling in the right iliac fossa and right flank. Serology gave negative results but ultrasonography and CT scan images were suggestive of a hydatid cyst of the psoas muscle. A cystectomy was followed by total recovery. Hydatid cysts are rarely detected in France and their clinical and diagnostic characteristics are discussed. Ultrasonography and particularly CT scaner imaging are effective diagnostic procedures, avoiding unnecessary needle punctures and enabling adequate therapeutic measures to be instituted.

Adult↗
PubMedDate not supplied

Group A streptococcal necrotizing fasciitis of the psoas muscle.

Group A streptococci are common colonizers of the skin and upper respiratory tract. Serious infections of the respiratory tract as well as the skin and soft tissue are common. Highly virulent Group A streptococci are not infrequently the cause of invasive, life-threatening infections. Necrotizing fasciitis is uncommon and rarely the result of Group A streptococci. Necrotizing fasciitis of the psoas from Group A streptococci has been reported as a complication in patients with colon cancer perforation or peritonitis. We report the first case of Group A streptococcal necrotizing fasciitis of the psoas muscle not associated with peritonitis or colon perforation.

Adult↗
PubMed1988

The role of calcium ions in the activation of rabbit psoas muscle.

This study tested the effects of free Ca++ on both the small-amplitude mechanical behaviour (dynamic stiffness and phase between 1 and 500 Hz) and the large-scale filament-sliding behaviour (Vmax) of single fibres of chemically-activated glycerol-extracted rabbit psoas muscle. Small-amplitude vibrations (0.1% peak-to-peak of initial length L0) were used to elicit fw, the frequency for maximum oscillatory work-production per cycle. The unloaded contraction velocity Vmax was measured during the same contractions, using the slack-test method with shortening length steps of up to 10% L0. These produced nonlinear length-time plots demonstrating that the unloaded contraction velocity was not constant as contraction progressed, but fell with time. This behaviour was approximated by two velocities, V1 the velocity observed for about the first 15 ms and V2 the velocity after this time. V1 and V2 were found to have different sensitivities to Ca++. The value of V2 fell as the level of [Ca++] was reduced, and was linearly proportional to the active tension over the range 0.2 Pmax to Pmax (where Pmax is the isometric tension for saturating amounts of Ca++). In contrast to this V1 remained insensitive to changes in [Ca++] for levels of activation corresponding to active tensions ranging from Pmax to 0.6 Pmax, and then fell as the level of activation was further reduced. It was found that the level of [Ca++] did not affect the magnitude of fw over the range of concentrations yielding active tensions from 0.2 Pmax to Pmax. These results are discussed in terms of the kinetic processes underlying transient readjustments to perturbations from isometric equilibrium.

Animals↗
PubMed2000

Cross-bridge attachment during high-speed active shortening of skinned fibers of the rabbit psoas muscle: implications for cross-bridge action during maximum velocity of filament sliding.

To characterize the kinetics of cross-bridge attachment to actin during unloaded contraction (maximum velocity of filament sliding), ramp-shaped stretches with different stretch-velocities (2-40,000 nm per half-sarcomere per s) were applied to actively contracting skinned fibers of the rabbit psoas muscle. Apparent fiber stiffness observed during such stretches was plotted versus the speed of the imposed stretch (stiffness-speed relation) to derive the rate constants for cross-bridge dissociation from actin. The stiffness-speed relation obtained for unloaded shortening conditions was shifted by about two orders of magnitude to faster stretch velocities compared to isometric conditions and was almost identical to the stiffness-speed relation observed in the presence of MgATPgammaS at high Ca(2+) concentrations, i.e., under conditions where cross-bridges are weakly attached to the fully Ca(2+) activated thin filaments. These data together with several control experiments suggest that, in contrast to previous assumptions, most of the fiber stiffness observed during high-speed shortening results from weak cross-bridge attachment to actin. The fraction of strongly attached cross-bridges during unloaded shortening appears to be as low as some 1-5% of the fraction present during isometric contraction. This is about an order of magnitude less than previous estimates in which contribution of weak cross-bridge attachment to observed fiber stiffness was not considered. Our findings imply that 1) the interaction distance of strongly attached cross-bridges during high-speed shortening is well within the range consistent with conventional cross-bridge models, i.e., that no repetitive power strokes need to be assumed, and 2) that a significant part of the negative forces that limit the maximum speed of filament sliding might originate from weak cross-bridge interactions with actin.

Actins↗
PubMed1988

Femoral obturator and sciatic neurectomy with iliacus and psoas muscle section for spasticity following spinal cord injury.

The treatment of severe refractory spasticity following spinal cord injury may raise challenging therapeutic problems. Classical approaches involve various types of myelotomies, rhizotomies and intrathecal injections of neurolytic substances. Alternative approaches include percutaneous rhizotomies and, more recently, the possible use of electrical stimulation of the spinal cord. Certain cases, however, may not be amenable to commonly accepted techniques. An operative technique is presented which involves a suprapubic incision for an infraperitoneal approach to a femoral and obturator neurectomy and an incision of the iliacus and psoas muscles bilaterally. This may be followed, when indicated, by a bilateral infragluteal section of the sciatic nerves. This technique offers a viable surgical alternative to the treatment of spasticity following spinal cord injury in cases where other traditional methods are contraindicated or have failed.

Adolescent↗
PubMed1999

Contractile properties of rabbit psoas muscle fibres inhibited by beryllium fluoride.

The structure of truncated, recombinant Dictyostelium myosin motor domain complexed with Mg.ADP and slowly dissociating analogues of Pi has previously been characterized as two main states (S1-MgADP plus BeFx vs. A1F4- or Vi). The BeFx bound state is thought to mimic the weak actin-binding M.ATP complex, while the states with A1F4- or Vi bound mimic the M.ADP.Pi state. While the effects of A1F4- and Vi on fibre mechanics have been previously described (Chase et al., 1994, 1993), the effects of BeFx have not been characterized in detail. At pCa 4.5 (12 degrees C), we measured (i) steady-state isometric tension, (ii) stiffness (KS; 1 kHz sinusoids), and (iii) unloaded shortening velocity (Vu; slack test) in single skinned muscle fibres from rabbit psoas. Results were compared when tension was inhibited with either BeFx or 2,3-butanedione-monoxime (BDM) or modulated by altering myoplasmic [Ca2+]. With 3 mM total fluoride, 1 mM BeFx inhibited both tension and KS by approximately 50% (compared to 7-10 mM BDM and 50-100 microM A1F4-). Increasing [BeFx] to 10 mM further reduced tension to approximately 15% P0, but had little further effect on KS; with BDM and altered [Ca2+], KS scaled more proportionately with tension. Inhibition of tension and KS by BeFx was more rapidly reversible, compared with slow recovery from tension inhibition with A1F4- or Vi. Vu exhibited a complex dependence on [BeFx], being relatively unaffected by concentrations < or = 1 mM, and becoming inhibited steeply for [BeFx] above this level. With BDM, Vu co-varied more directly with force. Our results suggest that BeFx may induce a different cross-bridge state in fibres than do A1F4- or Vi, but all three analogues of Pi form complexes that mimic crossbridge states that follow ATP hydrolysis.

Animals↗
PubMed1997

Modulation of cross-bridge affinity for MgGTP by Ca2+ in skinned fibers of rabbit psoas muscle.

Previously we reported that saturation of cross-bridges with MgATP gamma S in skinned muscle fibers was calcium sensitive. In the present study we investigate whether this observation can be generalized to other nucleotides by studying saturation of cross-bridges with MgGTP. In solution, myosin-subfragment 1 (S1) in the presence of 10 mM MgGTP was found to bind to actin with low affinity, similar to that in the presence of MgATP and MgATP gamma S. In EGTA buffer, the equatorial x-ray diffraction intensity ratio I11/I10 recorded in single skinned fibers decreased upon increasing MgGTP concentration from 0 to 10 mM (1 degree C and 170 mM ionic strength). The I11/I10 ratio leveled off at 10 mM MgGTP, indicating full saturation of cross-bridges with the nucleotide. Under these conditions, the value of I11/I10 is indistinguishable from that obtained in the presence of saturating [MgATP]. In CaEGTA buffer, however, the decrease in I11/I10 occurs over a wider range of concentrations, and there is no indication of I11/I10 leveling off at 10 mM MgGTP, suggesting that full saturation is not reached. The Ca2+ dependence of GTP binding appears to be a direct consequence of the differences in the affinities of the strongly bound cross-bridges to actin versus weakly bound cross-bridges to actin. A biochemical scheme that could qualitatively explain the titration behavior of ATP gamma S and GTP is presented.

Adenosine Triphosphate↗
PubMed1999

Kinetics of thin filament activation probed by fluorescence of N-((2-(iodoacetoxy)ethyl)-N-methyl)amino-7-nitrobenz-2-oxa-1,3-diazole-labeled troponin I incorporated into skinned fibers of rabbit psoas muscle: implications for regulation of muscle contraction.

Making use of troponin with fluorescently labeled troponin I subunit (N-((2-(iodoacetoxy)ethyl)-N-methyl)amino-7-nitrobenz-2-oxa-1, 3-diazole-troponin I, IANBD-TnI) that had previously been described in solution studies as a probe for thin filament activation (. Proc. Natl. Acad. Sci. 77:7209-7213), we present a new approach that allows the kinetics of thin filament activation to be studied in skinned muscle fibers. After the exchange of native troponin for fluorescently labeled troponin, the fluorescence intensity is sensitive to both changes in calcium concentration and actin attachment of cross-bridges in their strong binding states (. Biophys. J. 77:000-000). Imposing rapid changes in the fraction of strongly attached cross-bridges, e.g., by switching from isometric contraction to high-speed shortening, causes changes in thin filament activation at fixed Ca(2+) concentrations that can be followed by recording fluorescence intensity. Upon changing to high-speed shortening we observed small (<20%) changes in fluorescence that became faster at higher Ca(2+) concentrations. At all Ca(2+) concentrations, these changes are more than 10-fold faster than force redevelopment subsequent to the period of unloaded shortening. We interpret this as an indication that equilibration among different states of the thin filament is rapid and becomes faster as Ca(2+) is raised. Fast equilibration suggests that the rate constant of force redevelopment is not limited by changes in the activation level of thin filaments induced by the isotonic contraction before force redevelopment. Instead, our modeling shows that, in agreement with our previous proposal for the regulation of muscle contraction, a rapid and Ca(2+)-dependent equilibration among different states of the thin filament can fully account for the Ca(2+) dependence of force redevelopment and the fluorescence changes described in this study.

Actin Cytoskeleton↗