Are the polarization colors of Picrosirius red-stained collagen determined only by the diameter of the fibers?

Summary Polarization colors of various purified collagens were studied in fibers of similar thickness. Three different soluble collagens of type I, insoluble collagen type I, lathyritic collagen type I, two p-N-collagens type I, pepsin extract collagen type II, two soluble collagens type III, p-N-collagen type III, and soluble collagen type V were submitted to a routine histopathologic procedure of fixation, preparation of 5-m-thick sections, staining with Picrosirius red and examination under crossed polars. Polarization colors were determined for thin fibers (0.8 m or less) and thick fibers, (1.6–2.4 m). Most thin fibers of collagens and p-N-collagens showed green to yellowish-green polarization collors with no marked differences between the various samples. Thick fibers of all p-N-collagens, lathyritic and normal 0.15 M NaCl-soluble collagens showed green to greenish-yellow polarization colors, while in all other collagens, polarization colors of longer wavelengths (from yellowish-orange to red) were observed. These data suggested that fiber thickness was not the only factor involved in determining the polarization colors of Picrosirius red-stained collagens. Tightly packed and presumably, better aligned collagen molecules showed polarization colors of longer wavelengths. Thus, packing of collagen molecules and not only fiber thickness plays a role in the pattern of polarization colors of Picrosirius red-stained collagens.     

Are the polarization colors of picrosirius red-stained collagen determined only by the diameter of the fibers?

Polarization colors of various purified collagens were studied in fibers of similar thickness. Three different soluble collagens of type I, insoluble collagen type I, lathyritic collagen type I, two p-N-collagens type I, pepsin extract collagen type II, two soluble collagens type III, p-N-collagen type III, and soluble collagen type V were submitted to a routine histopathologic procedure of fixation, preparation of 5-microns-thick sections, staining with Picrosirius red and examination under crossed polars. Polarization colors were determined for thin fibers (0.8 micron or less) an thick fibers, (1.6-2.4 microns). Most thin fibers of collagens and p-N-collagens showed green to yellowish-green polarization colors with no marked differences between the various samples. Thick fibers of all p-N-collagens, lathyritic and normal 0.15 M NaCl-soluble collagens showed green to greenish-yellow polarization colors, while in all other collagens, polarization colors of longer wavelengths (from yellowish-orange to red) were observed. These data suggested that fiber thickness was not the only factor involved in determining the polarization colors of Picrosirius red-stained collagens. Tightly packed and presumably, better aligned collagen molecules showed polarization colors of longer wavelengths. Thus, packing of collagen molecules and not only fiber thickness plays a role in the pattern of polarization colors of Picrosirius red-stained collagens.     

What factors determine the number of nonmuscle myosin II in the sarcomeric unit of stress fibers?

Biomechanics and Modeling in Mechanobiology - Actin stress fibers (SFs), a contractile apparatus in nonmuscle cells, possess a contractile unit that is apparently similar to the sarcomere of...     

Neurotrophic control of the transmembrane Cl− pump in mammalian muscle fibers

Resting membrane potential of both innervated and denervated rat diaphragm muscle fibers was investigated when the concentration of potential-producing ions was changed in the external fluid and following treatment with furosemide. It was found that equilibrium potential ( ) equalled resting potential level in innervated muscle for Cl^–, but shifts to more positive values compared with resting membrane potential following section of the nerve. Furosemide retards development of post-denervation depolarization of the muscle membrane. It is deduced that trophic influences originating from the motor nerve activates the furosemide-sensitive Cl^– influx system, leading to raised intracellular concentration of Cl^–, a shift in (E_Cl) and depolarization of the muscle membrane.S. V. Kurashov Medical Institute, Minsitry of Health of the RSFSR, Kazan'. Translated from Neirofiziologiya, Vol. 19, No. 6, pp. 766–771, November–December, 1987.     

Is the SII portion of the cross-bridge in glycerinated rabbit psoas fibers compliant in the rigor state?

To see whether the SII portion of the cross-bridge in rigor fibers is longitudinally compliant, we chemically cross-linked with dimethyl suberimidate the entire rod portion (including the SII portion) of myosin onto the surface of thick filaments in glycerinated rabbit psoas fibers, and studied the effect of the SII fixation on the stiffness of the rigor fibers. The cross-linking of fiber segments with full filament overlap increased the rigor stiffness by approximately 25%. Almost the same absolute amount of the stiffness increase was also observed in rigor fibers with half- or no filament overlap after the cross-linking, and a similar but somewhat larger increment of stiffness was observed in fiber segments cross-linked in relaxing solution. These results indicate that the stiffness increase is not produced by the fixation of the SII portion onto the thick filament surface, but is caused instead by the cross-linking of some parallel elastic elements in muscle, and therefore indicate that the SII portion of the cross-bridge is hardly longitudinally compliant in rigor fibers.     

The β-helical domain of bacteriophage T4 controls the folding of the fragment of long tail fibers in a chimeric protein

The key stage of the infection of the Escherichia coli cell with bacteriophage T4, the binding to the surface of the host cell, is determined by the specificity of the long tail fiber proteins of the phage, in particular, gp37. The assembly and oligomerization of this protein under natural conditions requires the participation of at least two additional protein factors, gp57A and gp38, which strongly hinders the production of the recombinant form of gp37. To overcome this problem, a modern protein engineering strategy was used, which involves the construction of a chimeric protein containing a carrier protein that drives the correct folding of the target protein. For this purpose, the trimeric β-helical domain of another protein of phage T4, gp5, was used. It was shown that this domain, represented as a rigid trimeric polypeptide prism, has properties favorable for use as a protein carrier. A fragment of protein gp37 containing five pentapeptide repeats, Gly-X-His-X-His, which determine the binding to the receptors on the bacterial cell surface, was fused in a continuous reading frame to the C-terminus of the domain of gp5. The resulting chimeric protein forms a trimer that has the native conformation of gp37 and exhibits biological activity.     

The occurrence of “mixed” nuclear bag intrafusal fibers in the cat muscle spindle

Summary A total of 147 muscle spindles was studied histochemically in serial transverse sections of 42 cat tenuissimus muscle specimens. Nuclear bag₁, nuclear bag₂ and nuclear chain intrafusal muscle fibers were distinguished by the differential staining resulting from the reactions for myosin adenosine 5-triphosphatase and nicotinamide adenine dinucleotide tetrazolium reductase. The majority of intrafusal fibers were of the same histochemical type at both fiber poles. However, seven muscle spindles contained one nuclear bag fiber each that presented as a bag₁ in one pole and as a bag₂ in the other pole. These mixed nuclear bag fibers were found in spindles that also contained at least one bag₁ and one bag₂ fiber of equivalent histochemical presentation in both fiber poles. The mixed bag fibers displayed differences of apparent fiber diameter and relative polar length between the two fiber poles. The motor innervation pattern, as revealed by staining for cholinesterase, was also dissimilar between the two poles of mixed bag fibers. The study indicates that the spindle equatorial region may in some instances serve as a boundary between two morphologically and histochemically different poles of the same intrafusal fiber.     

A method for the staining of intraosseous nerve fibers using Sihler’s staining technique

Abstract

Understanding nerve fiber distribution in the jaw bone is important when performing invasive surgical treatments. Both microscopic and macroscopic anatomical techniques have been developed to study innervation. Conventional methods of removing and staining these structures, however, often alter structure and lack reproducibility of the resulting specimens. We sought to optimize Sihler’s staining technique to stain intraosseous nerves in mandibles. Four cadaver specimens were used. The best staining of intraosseous nerve fibers was achieved by using the Plank-Rychlo solution. When the Styrene monomer was used, the resulting transparency was better than that obtained with glycerin under the same conditions. No significant differences were found between Sihler's staining procedure performed according to the conventional method and the procedure in which the second decalcification step was omitted. Our results demonstrate that applying Sihler’s staining technique to bones makes them transparent and allows observation of nerves while preserving the external shape of the bone and maintaining the position of intraosseous nerve fibers. Our findings suggest our Sihler staining method for intraosseous nerve fibers can provide an intermediate resolution between macroscopic and microscopic techniques.     

Can muscle fibers be stable on the descending limbs of their sarcomere length-tension relations?

The authors of a paper published in this journal (Allinger et al. (1996) J. Biomechanics 29, 627–633) have concluded, based on a theoretical analysis, that muscle fibers may be stable even if some of their constituent sarcomeres have lengths falling on the descending limbs of their static length-tension relations. This note reconsiders the question of fiber stability and concludes that fibers are unstable if at least one of their sarcomeres is on the descending limb. A positive ‘short-range’ sarcomere stiffness has no effect on fiber stability, and a positive ‘effective stiffness’ of the whole fiber does not imply sarcomere stability.     

Is the VO2 slow component dependent on progressive recruitment of fast-twitch fibers in trained runners?

The goal of this study was to use spectral analysis of EMG data to test the hypothesis that the O2 uptake VO2) slow component is due to a recruitment of fast fibers. Thirteen runners carried out a treadmill test with a constant speed, corresponding to 95% of the velocity associated with maximal VO2. The VO2 response was fit with the classical model including three exponential functions. Electrical activity of six lower limb muscles (vastus lateralis, soleus, and gastrocnemius of both sides) was measured using electromyogram surface electrodes. Mean power frequency (MPF) was used to study the kinetics of the electromyogram discharge frequency. Three main results were observed: 1) a common pattern of the MPF kinetics in the six muscles studied was noted; 2) MPF decreased in the first part of the exercise, followed by an increase for all the muscles studied, but only the vastus lateralis, and gastrocnemius muscles of both sides increased significantly (P < 0.05); and 3) the beginning of the MPF increase of the four muscles mentioned above corresponded with the beginning of the slow component. Our results suggest a progression in the average frequency of the motor unit discharge toward the high frequencies, which coheres with the hypothesis of the progressive recruitment of fast-twitch fibers during the VO2 slow component. However, this interpretation must be taken with caution because MPF is the result of a balance between several phenomena.     

What controls the position,number, size,and distribution of neuromuscular junctions on rat muscle fibers?

This review focuses on mechanisms that determine the position, number, size, and distribution of neuromuscular junctions (NMJs) on skeletal muscle fibers. Most of the data reviewed derive from studies of ectopic NMJ formation on soleus (SOL) muscle fibers in adult rats, which recapitulates essential aspects of NMJ formation in normal development. Transplanted axons induce acetylcholine receptor (AChR) aggregates, which are multiple and irregularly distributed initially but subsequently undergo massive reorganization such that one or a few winners survive and reach a certain size while the rest are eliminated (the losers). Results obtained by blocking nerve activity early and stimulating the SOL electrically show that evoked muscle impulse activity is responsible for the growth of winners to a given size and the creation of refractory zones, about 0.75 long, on each side of the winners, in which the elimination of losers occurs. Consequently, when two or more aggregates or NMJs survive on one fiber, they are, on average, at least 1.5 mm apart. Locally applied neural agrin induces comparable aggregation of AChRs and other postsynaptic proteins on denervated SOL fibers and such aggregates undergo similar activity-dependent selection for survival or elimination in refractory zones. In a dose-dependent way, neural agrin alone also induces expression of ε-AChR subunits and stabilizes AChRs to a half-life of 10 days, as found at normal NMJs. It is argued that signs of prepatterning of innervation sites by intrinsic muscle mechanisms may refer to epiphenomena that play no important role in NMJ formation. The conclusion is that neural agrin initiates and then maintains NMJs where motor axons happen to contact receptive muscle fibers and that evoked muscle impulse activity then ensures that the NMJs reach their appropriate size, efficiency and spatial distribution along each fiber.     

Mechanism for sympathetic modulation of activity of cutaneous receptors (with Aδ fibers)

The afferent flow in A fibers from cutaneous receptors was studied in acute experiments with cats. A decline in the number of fibers activated during adequate receptor stimulation was observed at 5 and 35 sec after the excitation of sympathetic efferents. Similar changes in the afferent flow were recorded in identical time intervals after the preliminary stretching and cooling of the skin. The results obtained indicate that the quantitative characteristics of afferent flow during the first 30 sec after stimulation of the sympathetic chain are primarily due to the change in the mechanical state of the tissues surrounding the receptors.N. I. Lobachevskii Institute of Mathematics and Cybernetics, Gor'kii University. Translated from Neirofiziologiya, Vol. 17, No. 4, pp. 517–521, July–August, 1985.     

The potential of photosynthetic aquatic species as sources of useful cellulose fibers—a review

Photosynthetic aquatic species, i.e., micro- and macroalgae and fresh or salt water plants, contain cellulose or other fibrous materials potentially suitable for paper making. Photosynthetic aquatic species having cellulosic or fibrous characteristics necessary for paper production were reviewed. These characteristics include overall fiber content, fiber size and morphology, and fiber composition. Several species of algae and aquatic plants are reported to possess cellulose in quantities greater than 10 % of total dry weight, and in general, the cellulose content in aquatic species is lower than that of most wood species. Commercial application of these aquatic algal or plant materials has been limited to simple milling, and no commercial applications utilizing processes to isolate the cellulosic fibers from these materials have yet been found.     

Altered Ca2+ signaling in skeletal muscle fibers of the R6/2 mouse,a model of Huntington’s disease

Huntington’s disease (HD) is caused by an expanded CAG trinucleotide repeat within the gene encoding the protein huntingtin. The resulting elongated glutamine (poly-Q) sequence of mutant huntingtin (mhtt) affects both central neurons and skeletal muscle. Recent reports suggest that ryanodine receptor–based Ca²⁺ signaling, which is crucial for skeletal muscle excitation–contraction coupling (ECC), is changed by mhtt in HD neurons. Consequently, we searched for alterations of ECC in muscle fibers of the R6/2 mouse, a mouse model of HD. We performed fluorometric recordings of action potentials (APs) and cellular Ca²⁺ transients on intact isolated toe muscle fibers (musculi interossei), and measured L-type Ca²⁺ inward currents on internally dialyzed fibers under voltage-clamp conditions. Both APs and AP-triggered Ca²⁺ transients showed slower kinetics in R6/2 fibers than in fibers from wild-type mice. Ca²⁺ removal from the myoplasm and Ca²⁺ release flux from the sarcoplasmic reticulum were characterized using a Ca²⁺ binding and transport model, which indicated a significant reduction in slow Ca²⁺ removal activity and Ca²⁺ release flux both after APs and under voltage-clamp conditions. In addition, the voltage-clamp experiments showed a highly significant decrease in L-type Ca²⁺ channel conductance. These results indicate profound changes of Ca²⁺ turnover in skeletal muscle of R6/2 mice and suggest that these changes may be associated with muscle pathology in HD.     

A proposal to evaluate the fibers’ break probability in ligaments and tendons

Understanding the yield and failure mechanisms of ligaments and tendons is important to have a deeper knowledge of their structure and function. Evaluating what are the limits of the human body is also important to prevent injuries in workers, in athletes and the elderly. The tissue yield mechanism was analyzed by modifying and extending a probabilistic model of collagen bundles. Since not usable experimental data are available in the literature, the model and the method were tested using Monte Carlo simulations. The simulations showed many crucial aspects of the model and gave some indications about possible future real validation experiments. The analysis of the correlation between the simulated data, the model ($R^2$) and the Signal-to-Noise-Ratio (SNR) highlighted the most important parameters that affect effectiveness of the described method: number of fibers, elongation step, noise. This analysis also showed that the numerical differentiation algorithms of the data have a key role on the accuracy of the yield assessment. However, the results also showed that the method is able to correctly estimate the elongation break distribution of the fibers of ligaments and tendons.     

Water in crystalline fibers of dihydrate β-chitin results in unexpected absence of intramolecular hydrogen bonding

The complete crystal structure (including hydrogen) of dihydrate β-chitin, a homopolymer of N-acetylglucosamine hydrate, was determined using high-resolution X-ray and neutron fiber diffraction data collected from bathophilous tubeworm Lamellibrachia satsuma. Two water molecules per N-acetylglucosamine residue are clearly localized in the structure and these participate in most of the hydrogen bonds. The conformation of the labile acetamide groups and hydroxymethyl groups are similar to those found in anhydrous β-chitin, but more relaxed. Unexpectedly, the intrachain O3-H...O5 hydrogen bond typically observed for crystalline β,1-4 glycans is absent, providing important insights into its relative importance and its relationship to solvation.     

A model for the dynamic properties of integrating fibers: Target localization in a three-dimensional space—II. Computer simulation

• 1.1. The stimulation sequence provoked by a luminous point moving in front of a column of ommatidia was simulated for the eye of Squilla mantis.
• 2.2. The output from the ommatidia is transferred to one tangential, integrating fiber as graded potentials. These potentials follow a gaussian-shaped angular sensitivity function for each ommatidium.
• 3.3. The tangential fiber sums the inputs as they arrive and generates a spike if the sum is above threshold at one instant of time and at one point of the fiber.
• 4.4. The histograms of instantaneous frequencies of spike discharge resemble the input-pattern histograms.
• 5.5. The discharge pattern changes with distance and speed of the moving spot as well for the simulations as in electrophysiological recordings, and is adapted to the size of the animal.
• 6.6. The shape of the histograms (i.e. the pattern of spike discharge) is assumed to transmit the information on the position, speed and size of a moving target.

     

Effect of cortisone on the developmental pattern of the neutral and the acid β-galactosidases of the small intestine of the rat

1. The developmental pattern and effect of cortisone on acid beta-galactosidase and neutral beta-galactosidase were studied in postnatal rats by a recently proposed method for their independent determination. 2. After birth the acid beta-galactosidase activity increases in the ileum, whereas it decreases slightly in the jejunum. On day 16 after birth the activity in the ileum decreases and in 20-day-old rats activity in both parts of the intestine decreases to adult values. In suckling animals the activity in the ileum exceeds the jejunal activity severalfold and in adult animals the activity in the jejunum is slightly higher than that in the ileum. 3. Neutral beta-galactosidase activity is high after birth and decreases in both jejunum and ileum after day 20 after birth. In 12-20-day-old rats activity in both parts is essentially the same, but in adult animals jejunal activity exceeds ileal activity four-to five-fold. 4. Cortisone (0.5, 2.0 or 5.0mg/100g body wt. daily for 4 days) does not influence the activity of either enzyme in 60-day-old rats. Acid beta-galactosidase activity is decreased after cortisone treatment in 8-, 12-, 16-and 18-day-old rats, with sensitivity to cortisone increasing with the approach of weaning. No effect of cortisone on acid beta-galactosidase is seen in 8-day-old rats. Neutral beta-galactosidase activity is increased in the ileum of 8-, 12-, 16- and 18-day old rats, but only in the jejunum of 8-and 12-day-old rats.