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PubMed2000

Contractility of single myofibrils of rabbit skeletal muscle studied at various MgATP concentrations.

A novel experimental method was developed to study the contractility of single myofibrils of skeletal muscle. Single myofibrils (ca. 1 microm in diameter) prepared from glycerinated rabbit psoas muscle were suspended between rigid and flexible microneedles by the entwining method. The length changes of the preparations applied via the rigid microneedle by an actuator and the force produced were measured by photo-electrically detecting the nanometer deflections of the flexible microneedle. Single myofibril preparations maintained uniform sarcomere striations during contraction-relaxation cycles. The isometric force produced, the velocity of unloaded shortening, and the force-velocity relationship of single myofibrils were investigated at various MgATP concentrations. The contractility of single myofibrils thus obtained in the absence of ATP regenerative systems was essentially the same as that of skinned muscle fibers under comparable conditions in the presence of ATP regenerative systems. Thus, it was found that (1) the present experimental method is useful for studying the contractility of single myofibrils, and (2) in single myofibril preparations, the MgATP concentration at actomyosin sites is well equilibrated with that in bathing solutions.

Adenosine Triphosphate↗
PubMed1998

Pelvic extension of retroperitoneal fluid: analysis in vivo.

OBJECTIVE: The purposes of this study were to describe the pathway of fluid flow from the retroperitoneal space into the pelvic extraperitoneal space on CT in vivo, to clarify the relation between its occurrence and the site or amount of retroperitoneal fluid, and to delineate the anatomic relation between the retroperitoneal spaces and the pelvic extraperitoneal space. MATERIALS AND METHODS: We reviewed the CT scans of 37 patients with retroperitoneal fluid collections. Patients who had undergone pelvic laparotomy and patients who had either fascial thickening alone or fluid within muscle (such as the psoas muscle or iliac muscle) alone were excluded. RESULTS: Fluid extension into the pelvic extraperitoneal space was seen in six patients (16%). Extension by the infrarenal extraperitoneal space was seen in all six of these patients, but extension by properitoneal fat was seen in only one of the six patients. In patients with large amounts of fluid in the infrarenal extraperitoneal space, we frequently saw extension into the pelvic extraperitoneal space. Extension of pancreatic fluid into the infrarenal extraperitoneal space occurred in only 15% of the 37 patients. However, it occurred in both patients with ruptured abdominal aortic aneurysms. Three pathways from the infrarenal extraperitoneal space into the pelvic extraperitoneal space were seen: extension dorsally medial to the iliac vessels (n = 6), extension dorsally lateral to the iliac vessels (n = 1), and extension medially into the prevesical space (n = 2). Coexistence of two of these three pathways was seen in three patients. CONCLUSION: In vivo, extension of retroperitoneal fluid into the pelvic extraperitoneal space is not rare and occurs more often by the infrarenal extraperitoneal space than by properitoneal fat. Extension of retroperitoneal fluid to the infrarenal extraperitoneal space can be attributed less frequently to sources distant to the pelvic cavity such as pancreatic fluid. Such extension often derives from sources that can produce large amounts of retroperitoneal fluid such as ruptured abdominal aortic aneurysms. Of the three pathways from the infrarenal extraperitoneal space to the pelvic extraperitoneal space, dorsal extension medial to the iliac vessels is the most common, and multiple pathways often coexist.

Body Fluids↗
PubMed1999

[Space-occupying lesions in the iliopsoas space: a challenge in the Department of Internal Medicine].

Mass lesions in the iliopsoas compartment (MLIPC) are uncommon in patients in departments of medicine and their incidence and etiologies are unclear. In a prospective study we diagnosed various MLIPCs in 7 patients during a 10-year period, representing 0.03% of admissions. Symptoms included abdominal or flank pain (4 cases), pain along the thigh (5), diminished psoas muscle strength (2), fever (2), and hypotension (1). MLIPC was suspected on clinical grounds in 5 cases. In all cases the diagnosis was established by computed tomography (CT). Tissue was sampled by needle biopsy in 4 and on surgery in 1. MLIPCs were caused by hemorrhage (2), infection (2), neoplasia (2) and inflammatory mass (1). Often MLIPCs are life-threatening so their timely diagnosis by early CT scan is important.

Adult↗
PubMed1994

A birefringence study of changes in myosin orientation during relaxation of skinned muscle fibers induced by photolytic ATP release.

The birefringence of isolated skinned fibers from rabbit psoas muscle was measured continuously during relaxation from rigor produced by photolysis of caged ATP at sarcomere length 2.8-2.9 microns, ionic strength 0.1 M, 15 degrees C. Birefringence, the difference in refractive index between light components polarized parallel and perpendicular to the fiber axis, depends on the average degree of alignment of the myosin head domain with the fiber axis. After ATP release birefringence increased by 5.8 +/- 0.7% (mean +/- SE, n = 6) with two temporal components. A small fast component had an amplitude of 0.9 +/- 0.2% and rate constant of 63 s-1. By the completion of this component, the instantaneous stiffness had decreased to about half the rigor value, and the force response to a step stretch showed a rapid (approximately 1000 s-1) recovery phase. Subsequently a large slow birefringence component with rate constant 5.1 s-1 accompanied isometric force relaxation. Inorganic phosphate (10 mM) did not affect the fast birefringence component but accelerated the slow component and force relaxation. The fast birefringence component was probably caused by formation of myosin.ATP or myosin.ADP.Pi states that are weakly bound to actin. The average myosin head orientation at the end of this component is slightly more parallel to the fiber axis than in rigor.

Adenosine Triphosphate↗
PubMed2003

Stretch-induced force enhancement and stability of skeletal muscle myofibrils.

The main purpose of the experiments presented in this chapter was to test the hypothesis that the stretch-induced force enhancement commonly observed in skeletal muscle is associated with sarcomere length instability. Single myofibrils isolated from the rabbit psoas muscle were attached to a nanolever pair for force measurement at the one end, and to a glass needle for controlled displacements at the other end. The image of the striation pattern was projected onto a linear 1024-element photodiode array, which was scanned (20 Hz) to produce a dark-light pattern corresponding to the A- and I-bands, respectively. Starting from a mean SL of approximately 2.55 microm, stretches of a nominal amplitude of 4 to 10% of SL, at a nominal speed of 100 nm x sec(-1) were applied to activated myofibrils (pCa2+ = 4.75). Following stretch, the isometric, steady-state force was greater by 10.9% to 45.9% than the force produced before stretch, and was greater than the force predicted at the corresponding final length. Passive force could not account for the force enhancement. Sarcomere lengths along the activated myofibrils were non-uniform, but remained constant before stretch or during the extended isometric period after stretch. Further, sarcomeres never stretched to a length beyond thick and thin filament overlap. It is concluded that sarcomeres are stable, and therefore the increased force observed after stretch must be a sarcomeric property, not associated with continuous length changes of unstable sarcomeres, as had been assumed in the past.

Animals↗
PubMed2001

Single turnover of cross-bridge ATPase in rat muscle fibers studied by photolysis of caged ATP.

A mechanical study on skinned rat psoas muscle fibers was performed at about 16 degrees C with X-ray diffraction and caged-ATP photolysis. The amount of photoreleased ATP was set < 0.2 mM for analysis of a 'single turnover' of the cross-bridge ATPase. With regard to the phase of activation, the results under the single turn-over condition were generally consistent with previous results obtained with larger amount of photoreleased ATP. Formation of the ADP-rigor state was mechanically monitored by the 90 degrees out-of-phase component of stiffness at 500 Hz, which was elevated on activation and then decreased to zero with a half-time of 0.2-0.3 s. Intensity changes of the X-ray reflections (e.g. equatorial reflections, actin layer lines and a myosin meridional reflection) indicated that a large number of cross-bridges returned to the rigor structure with a half-time of 0.5-0.7 s. During this phase, tension did not increase but slowly decreased with a half-time of about 1.0 s. The in-phase stiffness increased only 20-30% at the most. These results indicate that, even if the number of cross-bridges formed at any moment during full contraction is small, they can interact with actin and form rigor bonds with a rate of 1 s(-1). The force developed in the rigor formation is probably lost due to the presence of rigor bridges and compliance in the preparation.

Adenosine Diphosphate↗
PubMed1992

Radiographic demonstration of paraspinal muscle wasting in patients with chronic low back pain.

This study investigated whether paraspinal muscle wasting occurs in association with chronic low back pain (LBP). Cross-sectional areas (CSA) of spinal and paraspinal structures were measured radiographically, at the level of L4, in 43 patients with recent and 44 with chronic LBP. Crude anthropometry demonstrated no differences between the groups with regard to L4 and paraspinal and psoas muscle CSAs, but inter-individual differences were large. Since body weight correlated significantly with L4 CSA this dimension was used as an 'internal standard' and further inter-individual comparisons were made using paraspinal: L4 and psoas: L4 (i.e. muscle to bone) CSA ratios. Muscle assessments made in this 'relative' fashion revealed significant reductions in paraspinal and psoas dimensions in patients with chronic compared to recent onset LBP. These changes could cause paraspinal and psoas muscle weakness and thereby predispose to spinal instability and progressive dysfunction.

Adult↗
PubMed1993

MR relaxation times and fiber type predominance of the psoas and multifidus muscle. An autopsy study.

MR relaxation times, fiber composition, nonmyofiber space, water content, and fat content of human psoas and multifidus muscle samples of 10 male cadavers were studied in vitro. The T1 and T2 relaxation times of multifidus muscle were significantly longer than those of the psoas muscle. On average, type 1 fibers (slow fibers with a small cross-sectional diameter) predominated in both muscles. There was no correlation between the relative mass of type 1 or 2 fibers (fast fibers with a large cross-sectional diameter) or nonmyofiber space and the relaxation times. The quantity of fat in the muscle did not correlate with the relaxation times either.

Adolescent↗
PubMed2000

[Groin pain in athletes: role of magnetic resonance].

INTRODUCTION: Aim of our work was to evaluate the diagnostic role and potentials of Magnetic Resonance Imaging (MRI) in the study of groin pain in athletes and in the differential diagnosis among the pathological conditions that cause this syndrome. MATERIAL AND METHODS: MRI examinations were performed with a 1.5 T superconductive magnet, and a 0.2 T permanent magnet. Spin-Echo (SE) T1-w, PD, SE T2-w, Gradient-Echo (GE) T2-w and fat saturation sequences were used, on axial, sagittal and coronal scan planes. We performed MRI on twenty-five athletes (22 men and 3 women; age range 17 to 32 years) with chronic groin pain of questionable origin who had been complaining of it for at least 6 months. In 22 cases, radiographs were available; Computed Tomography (CT) had been performed in 3 cases and Ultrasound (US) in 7 cases. Nine patients were submitted to MRI after the symptoms had disappeared. RESULTS: In all patients, MRI provided an accurate depiction of pubic bone alterations and of adjacent myotendinous structures. In 14 cases, osteitis pubis was diagnosed, which was bilateral in 2 cases only (muscular asymmetry of the rectus abdominis was found in 4 of these patients); 4 patients had myotendinous posttraumatic changes (1 hematoma of the psoas muscle and 3 injuries of the abductor muscles of the thigh); 4 patients presented isolated dysmetria of rectus abdominis muscles, with unilateral involvement of the sacroiliac joint in 1 patient; 3 patients had inguinal hernia, surgically confirmed in all cases. DISCUSSION: Osteitis pubis, intended as reactive intraspongiuos edema of the pubic bones, is the most frequent cause of groin pain in athletes. In the early diagnostic phases, both plain films and CT may be negative or not specific. On the other hand, MRI has always proved to be a valuable diagnostic technique in detecting the osteitic change as an area of low signal intensity on T1-w images and of high and homogeneous signal intensity on T2-w scans without fat suppression. Dysmetria of the straight muscles of the abdomen, which may be associated, is always well depicted by MRI on axial planes. Both posttraumatic and dysmetric changes of the muscular structures adjacent to the pubis are well documented by US and MRI. The latter, however, thanks to its multiplanar capabilities, allows better spatial assessment of the alteration, especially if located at peri-insertional level. Possible associated diseases such as the involvement of the sacroiliac joints are also well shown by MRI. Inguinal hernias are easily demonstrated by MRI, which allows the direct visualization of the hernial sac within the inguinal canal. CONCLUSIONS: In our experience, only MRI can permit an accurate and early diagnosis of the different sport-related pubic conditions. MRI is also a valuable tool in monitoring the alterations with reference to their response to treatment, which may also help bring the athletes back to their activities.

Abdominal Muscles↗
PubMed2003

Force enhancement by PEG during ramp stretches of skeletal muscle.

We have investigated the effects of a stronger actomyosin bond on force (Ps) during rapid stretch of active permeabilized rabbit psoas muscle fibers as a function of temperature from 5 to 30 degrees C. The strength of the actomyosin bond is enhanced by addition of polyethylene glycol (PEG), especially in pre-powerstroke states [Chinn et al. (2000) Biophys J 49: 437-451]. We have hypothesized that such states produce much of the force when activated muscles are stretched [Getz et al. (1998) Biophys J 75: 2971-2983]. Addition of PEG to activated fibers produced a small increase in isometric tension, Po (50-90 kN/m2), which was approximately independent of temperature. In contrast PEG produced a dramatic increase in Ps at low temperatures (200-300 kN/m2), but a modest increase at higher temperatures (70-90 kN/m2). We also measured Ps and Po in solutions containing the phosphate analog aluminum fluoride (AlF4) with and without PEG. In the absence of PEG, AlF4 reduced Po much more than Ps. Addition of PEG did not enhance Po, but enhanced Ps significantly. The contrasting effects of PEG on Ps and Po, and the effect of temperature can be explained by a model in which stretch force is produced by pre-powerstroke cross-bridges whose maximum distension is increased by PEG, and isometric force is produced by strongly bound cross-bridges whose bond strength is also enhanced by PEG, but to a lesser extent.

Actomyosin↗
PubMed1994

Ultrastructural changes in glycerol-extracted skeletal muscle fibers after chemical modification of myosin heads with p-phenylenedimaleimide.

We examined the structural changes in relaxed glycerinated rabbit psoas muscle fibers induced by modification of the myosin heads with p-phenylenedimaleimide (p-PDM), which reacts with sulfhydryls on the myosin head to cause its loss of ability to combine with actin and to hydrolyse ATP. In the longitudinal sections of both chemically fixed and quickly frozen muscle fibers, ladder-like structures, interpreted as the myosin heads extending nearly at right angles with the thick filaments, were more prominent in the p-PDM-modified fibers than in the control fibers. Fourier transform diffractograms of the longitudinal sections exhibited a distinct 14.3-nm meridional reflection, which arises from axial spacing of the myosin heads on the thick filament, in the p-PDM-modified fibers, but not in the control fibers. These results indicate that the p-PDM-modification of the myosin heads causes an increase in the regularity of myosin head arrangement on the thick filament.

Animals↗
PubMed1998

Calcium regulation of tension redevelopment kinetics with 2-deoxy-ATP or low [ATP] in rabbit skeletal muscle.

The correlation of acto-myosin ATPase rate with tension redevelopment kinetics (k(tr)) was determined during Ca(+2)-activated contractions of demembranated rabbit psoas muscle fibers; the ATPase rate was either increased or decreased relative to control by substitution of ATP (5.0 mM) with 2-deoxy-ATP (dATP) (5.0 mM) or by lowering [ATP] to 0.5 mM, respectively. The activation dependence of k(tr) and unloaded shortening velocity (Vu) was measured with each substrate. With 5.0 mM ATP, Vu depended linearly on tension (P), whereas k(tr) exhibited a nonlinear dependence on P, being relatively independent of P at submaximum levels and rising steeply at P > 0.6-0.7 of maximum tension (Po). With dATP, Vu was 25% greater than control at Po and was elevated at all P > 0.15Po, whereas Po was unchanged. Furthermore, the Ca(+2) sensitivity of both k(tr) and P increased, such that the dependence of k(tr) on P was not significantly different from control, despite an elevation of Vu and maximal k(tr). In contrast, lowering [ATP] caused a slight (8%) elevation of Po, no change in the Ca(+2) sensitivity of P, and a decrease in Vu at all P. Moreover, k(tr) was decreased relative to control at P > 0.75Po, but was elevated at P < 0.75Po. These data demonstrate that the cross-bridge cycling rate dominates k(tr) at maximum but not submaximum levels of Ca(2+) activation.

Adenosine Triphosphate↗