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At least 1,225 records · Page 68Linked to original sources
PubMed1994

Development of ischemic contracture in isolated skeletal muscles: relation to the capacity for anaerobic glycolysis.

In order to evaluate the dependence of the rate of ischemic contracture development in isolated skeletal muscles on the capacity for anaerobic glycolysis, factors affecting ischemic contracture development were examined using rat soleus and quadriceps muscles. The contracture developed faster in slow-twitch oxidative (SO) fibers than in fast-twitch glycolytic (FG) fibers. In both types of fibers, the rate of contracture development was inversely related to the medium pH. Addition of lactate increased the rate of contracture development. In FG fibers, the lactate level during contracture was directly, and the glycogen level inversely, proportional to the medium pH. An increase in muscle lactate level by 4-h swimming accelerated the contracture development, and reduced further lactate accumulation during contracture. Types of exercise training known to influence the capacity for anaerobic glycolysis (interval training and repeated fast climbing and swimming) decreased the velocity of contracture development. Isoprenaline administration in vivo accelerated contracture development in association with reduced lactate level during contracture. Swimming training counterbalanced the action of isoprenaline. Adrenalectomy accelerated contracture development in SO fibers, and decreased lactate accumulation during contracture in FG fibers. In adrenalectomized rats, the effects of exercise were more pronounced in SO fibers than in FG fibers. These results indicate that the rate of contracture development in isolated skeletal muscle is inversely related to the capacity for anaerobic glycolysis.

Adrenalectomy↗
PubMed2000

Potential of dual-skinned, high-flux membranes to reduce backtransport in hemodialysis.

BACKGROUND: Potential backfiltration of cytokine-inducing material is a clinical concern during hemodialysis conducted with high-flux membranes. Novel hollow-fiber membranes were developed that had asymmetric convective solute transport properties, aimed at reducing the passage of potentially harmful molecules from dialysate to blood, while maintaining the desired fluid and solute movement from blood to dialysate. METHODS: Sieving coefficient as a function of molecular weight was measured in vitro using polydisperse dextrans. Measurements were conducted using two different flat-sheet membranes in series or using hollow fiber membranes having two integrally formed skin layers. Based on measured experimental parameters, model calculations simulated the performance of a clinical-scale dialyzer containing these new membranes versus that of a commercially available high-flux dialyzer. RESULTS: Asymmetric convective solute transport was demonstrated using both commercial flat-sheet and newly developed hollow-fiber membranes. For two flat-sheet membranes in series, the extent of asymmetric transport was dependent on the order in which the solution was filtered through the membranes. For the hollow-fiber membranes, the nominal molecular weight cut-off was 20 kD in the blood-to-dialysate direction and 13 kD in the dialysate-to-blood direction. For this membrane, model calculations predict that clearance of a beta2-microglobulin-sized molecule (11,800 D) would be significantly greater from blood to dialysate than in the reverse direction, even under conditions of zero net ultrafiltration. CONCLUSION: A novel hollow-fiber dialysis membrane was developed that allows greater convective solute transport from blood to dialysate than from dialysate to blood.

Dextrans↗
PubMed1994

Laminar pattern of NADPH-diaphorase activity in the developing avian cerebellum.

The present study aimed to define the distribution of NADPH-diaphorase (NADPH-d) positive cells and fibers in the developing chick cerebellum. From embryonic day 9 (E9) until day E15 NADPH-d positive ascending axons, originating from pontine nuclei, targeted selectively the developing folia. Cerebellar cortex exhibited weak NADPH-d activity until day E15, when NADPH-d negative granule cells of external granular layer began inward migration. From that embryonic age, differentiated granule, Golgi II type cells and glomeruli of the internal granular layer exhibited gradually increasing diaphorase activity. In the molecular layer diffuse activity increased, possibly due to the development of the parallel fibers. Transient NADPH-d activity appeared on Purkinje somata (PC) at day E17 and by posthatching day 1 all PC were devoid of diaphorase activity. Our data support the hypothesis that neurons producing nitric oxide (NO) are involved in the activity dependent developmental processes for the establishment of connections and normal cytoarchitecture.

Amino Acid Oxidoreductases↗
PubMed1993

Fiber-optic sensor for continuous monitoring of fermentation pH.

We have developed a fiber-optic chemical sensor for on-line monitoring of fermentation pH. The sensor is based on a covalently bound fluorescent dye immobilized within a water-permeable polymer layer on an optical fiber. Measurements were performed on a portable fluorimeter and employed a ratiometric approach to account for system instabilities. We show that the use of this fiber-optic sensor provides fast, accurate and reliable measurements during E. coli fermentation in a complex medium.

Buffers↗
PubMed1996

Characterization of an erbium-doped fiber amplifier as a light source and development of a near-infrared spectrophotometer based on the EDFA and an acoustooptic tunable filter.

A novel light source for the near-infrared region which has the highest intensity and widest spectral bandwidth of all near-IR light sources has been developed. The system is based on a single-mode fiber (about 18 m long) doped with Er3+ ion. The doped ion produces amplified spontaneous emission (ASE) in the near-IR region (from 1500 to 1600 nm) when it is excited by a diode laser at 980 nm. Because the diode laser is fusion-spliced directly to the doped fiber, the system is compact, all-solid-state, reliable, and stable and requires little maintenance. Its ASE output intensity was found to be comparable with those of diode lasers currently available for this near-IR region and is much higher than those of conventional halogen-tungsten lamps and the so-called (high-intensity) superluminescent light emitting diodes (SLEDs). Its spectral bandwidth is, however, much wider than those of the diode lasers and the SLEDs. Even higher intensity can be obtained from the doped fiber when a low-intensity (1 mW) light from a 1550-nm laser diode is introduced into the doped fiber. The intensity is enhanced (up to 7 times compared to the ASE) because the input light is amplified by the doped fiber. Furthermore, the output intensity of this erbium-doped fiber amplifier (EDFA) can be appropriately adjusted to provide relatively higher output intensity at any range of wavelengths (within this 1500-1600-nm region) by simply changing the temperature and/or the driven current of the input diode laser. Subsequently, an acoustooptic tunable filter was used to provide a means to spectrally tune the EDFA rapidly and to develop an all-solid-state, compact near-IR spectrophotometer which not only is very sensitive, stable, and reliable but also has a very high throughput. This spectrophotometer can detect water in ethanol at a limit of detection of 10 ppm. More importantly, the high through-put makes it possible to use the instrument to measure spectra of highly absorbing samples (e.g., absorption spectrum of 1.0 M Pr3+ aqueous solution through four sheets of paper); measurements which are currently not possible with halogen-tungsten lamp-based spectrophotometers.

Amplifiers, Electronic↗
PubMed1983

Arguments in favour of endocytosis of glycoprotein components of the membranes of parallel fibers by Purkinje cells during the development of the rat cerebellum.

Chloroquine (a drug known to induce a dysfunction of lysosomes) was used to study the behavior of Concanavalin A binding glycoproteins located on the axolemma of parallel fibers in young rat cerebella, and abundant on these membranes at a period preceding synaptogenesis with the dendrites of Purkinje cells. Chloroquine induces in Purkinje cells a large accumulation of grains consisting of membrane whorls in lysosomes. These grains stain for Concanavalin A, and do not stain either for a mitochondrial marker (aspartate aminotransferase mitochondrial isoenzyme) or for a marker of the Purkinje cell internal membrane (PSG). It is suggested that the material accumulating in the Purkinje cells under the effect of chloroquine comes from the parallel fibers. Together with the observation that alpha-D-mannosidase (involved in the degradation of these glycoproteins) is exclusively located inside Purkinje cells, these results provide a firm indication that this material enters the Purkinje cells through pinocytosis. The absence of ATPase activity (ATPase is a glycoprotein plasma membrane marker highly concentrated on parallel fibers) within these grains suggested that not all the components of these membranes are pinocytosed, but that the process is specific for certain molecules. These results are compatible with the ultrastructural observations of others, and support the arguments in favour of the pinocytosis phenomenon being one of the first steps of synapse formation. The observed specificity of pinocytosis for certain molecules suggests that a receptor-mediated recognition of some glycans of glycoproteins is the preliminary event in the establishment of synapses.

Adenosine Triphosphatases↗
PubMed1992

Development and birthdates of vasoactive intestinal peptide immunoreactive neurons in the chick proventriculus.

To gain insight into the mechanisms regulating expression of transmitter phenotypes in the enteric nervous system, we have studied the development and birthdate of vasoactive intestinal peptide immunoreactive (VIP-IR) myenteric neurons in the chicken proventriculus (secretory portion of the avian stomach) by a combination of immunocytochemistry and radioautography. The appearance and numbers of VIP-IR neurons in whole mounts of the myenteric plexus from chick embryos and chickens were examined. We found that VIP-IR neurons first appeared at embryonic day (E) 5.5-6.5 in the distal part of the proventriculus. At E7.5, VIP-IR neurons were found singly, in pairs, or in small groups, which together with unlabeled cells formed primitive myenteric ganglia. VIP-IR fibers were found within the developing fiber tracts which connected the ganglia. The number of VIP-IR neurons was found to be maximum in the E15.5 embryo and to decline to 68% of maximum in the 4 week old chicken. Birthdate studies were performed by application of either single pulses or cumulative doses of [3H]-thymidine to embryos between E3 and E14. Whole mounts of the myenteric plexus from the proventriculus of these embryos were immunostained for VIP at E10 or E17. The whole mounts were subsequently sectioned and processed for radioautography. We found that VIP-IR myenteric neurons were born between E3 and E10 with a peak at E7. Most cells underwent terminal division between E5 and E9. These data will be useful in determining the time and conditions when cells make decisions about transmitter phenotypes.

Aging↗
PubMed2001

Development- and differentiation-dependent reorganization of intermediate filaments in fiber cells.

PURPOSE: To define the remodeling of lens fiber cell intermediate filaments (IF) that occurs with both development and differentiation. METHODS: Prenatal and postnatal mice were probed for the IF proteins phakosin, filensin, and vimentin, using light microscope immunocytochemical methodology. RESULTS: The pattern of vimentin accumulation in elongating fiber cells changed with development. Early in development vimentin first emerged predominantly as focal accumulations in the basal region of both epithelial and primary fiber cells. A light diffuse cytoplasmic staining was also noted. Later in embryonic development, and through maturity, vimentin in fiber cells was predominantly associated with the plasma membrane with no anterior-posterior polarity. Phakosin and filensin were first detected in the very latest stages of primary fiber elongation and continued to accumulate well after cells had completed elongation. Initially, these proteins accumulated in the anterior half of the fiber cells and were cytoplasmic in distribution. After P13, the pattern of initial distribution in differentiating fiber cells changed to a predominantly plasma membrane localization. Neither beaded filament protein showed focal basal accumulations. In mature lenses, all three proteins ultimately disappeared from the nuclear fiber cells. CONCLUSIONS: Beaded filament protein accumulation lags significantly behind both primary and secondary fiber cell elongation, suggesting a functional role subsequent to elongation. The subcellular distribution of vimentin and the beaded filament proteins showed marked differences within the cell, with differentiation, and with development. The differences in time of initial synthesis and in distribution of these IF proteins may bear on hypotheses about the role of IFs in fiber cell elongation and in structural-functional polarity of the fiber cell.

Animals↗
PubMed1993

Localisation of transforming growth factor beta 1 in developing muscles: implications for connective tissue and fiber type pattern formation.

Skeletal muscles are highly ordered mixtures of cell types, with each muscle having its own characteristic pattern of fiber types, connective tissues, and vasculature. The precursors of the myogenic and connective elements of a muscle are initially intermixed and are proliferating and differentiating together in a manner that generates an ordered array of mature cells. The molecular basis of myogenesis is unknown, although in vitro studies have revealed numerous putative regulators. The results obtained from in vitro studies are not easily related to in vivo myogenesis because of a lack of information about the localisation of the putative regulators in developing muscles. The objective of this paper was therefore to describe the spatial and temporal distribution of transforming growth factor beta 1 (TGF-beta 1), a small peptide that affects cultured fibroblasts, myoblasts, and vascular endothelial cells. TGF-beta 1-immunoreactivity was associated with the epimysia, perimysia, and vasculature of the developing muscles. The expression of TGF-beta 1 within developing muscles had a distinct spatial and temporal pattern that correlated with the fate of adjacent myotubes. Myotubes which formed prior to the expression of TGF-beta 1 developed into slow fibers whereas those which formed adjacent to TGF-beta 1-containing connective tissue matured into fast fibers. The possibility that TGF-beta 1 is involved in the generation of the pattern of epi- and perimysia and/or fiber types is discussed.

Animals↗
PubMed1970

Relations between structure and function in rat skeletal muscle fibers.

The fast-twitch extensor digitorum longus (EDL) and the slow-twitch soleus muscle of the rat consist of heterogeneous fiber populations. EDL muscle fibers differ in size, mitochondrial content, myoglobin concentration, and thickness of the Z line. The sarcoplasmic reticulum, on the other hand, is richly developed in all fibers, with only small variation. Myofibrils are clearly circumscribed at both the A and I band level. The soleus muscle is composed primarily of fibers with moderate mitochondrial content and myoglobin concentration. In most fibers the sarcoplasmic reticulum is poorly developed, with the exception of the portion of reticulum in phase with the Z line. As a consequence the myofibrillar fields are amply fused together. Contacts between sarcoplasmic reticulum and T system are discontinuous and may occur in the form of "dyads" instead of the typical triad structure. In a small proportion of soleus muscle fibers the organization and development of the sarcoplasmic reticulum is similar to that of EDL muscle fibers, with prominent fenestrated collars at the H band level. In these fibers mitochondria are larger and more abundant. The results are correlated with physiological studies on motor units in the same and in similar rat muscles. It is suggested that the variable structural pattern of rat muscle fibers is related to two distinct physiological parameters, speed of contraction and resistance to fatigue.

Animals↗
PubMed1990

Development of two morphological types of retinopetal fibers in chick embryos, as shown by the diffusion along axons of a carbocyanine dye in the fixed retina.

Centrifugal fibers to the retinas of chick embryos and hatched chicks have been examined and traced following staining by diffusion along their axonal membranes of the carbocyanine dye DiI in fixed tissue. In the older embryos and hatched chicks, the report of Dogiel (Arch. Mikrosk. Anat. 44:622-648, 1895) has been confirmed that there are two very different morphological types of centrifugal fiber. The restricted type ends as a relatively thick fiber, lacking varicosities, that runs for a short distance in the most sclerad level of the inner plexiform layer before terminating in a pericellular nest overlying the flask-shaped body of a single amacrine cell. Thin filaments occasionally leave the pericellular net, apparently to terminate on adjacent cells. The widespread type also runs in the most sclerad level of the inner plexiform layer, but it is thin, varicose, and highly branched, and its terminal arbor may span more than 1 mm, remaining at the same level. Both types of terminal arbor issue from parent axons in the optic fiber layer of the retina. A single parent axon gives either a single terminal fiber of the restricted type or several terminals of the widespread type, but never a mixture of the two. It is argued that the restricted and widespread types originate respectively from the neurons of the contralateral isthmo-optic nucleus and from the "ectopic" neurons scattered outside the isthmo-optic nucleus. In development, the centrifugal fibers reach the retina between E9 and E10 and initially run radially in the optic fiber layer, parallel to the retinofugal fibers but avoiding the dorsal retina. They dive into the inner plexiform layer at about E12. By E13, the terminal arbors are forming, and the widespread and restricted types can already be distinguished. The widespread type continues to increase its territory until about E18, and then appears to remain stable, whereas the restricted type attains its maximum ramification between E13 and E15 and then contracts. Prior to the retraction, the terminal territories of the restricted type fibers overlap, which may provide the anatomical basis for the interaxonal competition that apparently contributes to neuronal death in the isthmo-optic nucleus between E13 and E16. Axons of ganglion cells exhibit transient side branches between E11 and E13; these never reach as deep as the level where the centrifugal fibers run.

Animals↗
PubMed1985

Postnatal development of the anulospiral endings of Ia fibers in muscle spindles of mice.

The formation of the anulospiral ending of Ia fibers in muscle spindles was investigated in the masseter muscle of developing mice. Before 15 days after birth, the complete anulospiral ending was not observed in almost all of the muscle spindles examined. With the growth of mice, the Ia fiber began to construct the spiral ending, and by the 40th postnatal day after weaning, almost all of the Ia fibers of the muscle spindles had complete coiled endings, though the formation still continued in some spindles. The continuous formation of anulospiral endings for a long period after weaning indicates that muscle spindle morphogenesis may be affected by muscle tension in the masseter muscle due to the movement activated after weaning.

Animals↗
PubMed2003

The B-cell maturation factor Blimp-1 specifies vertebrate slow-twitch muscle fiber identity in response to Hedgehog signaling.

Vertebrate skeletal muscles comprise distinct fiber types that differ in their morphology, contractile function, mitochondrial content and metabolic properties. Recent studies identified the transcriptional coactivator PGC-1alpha as a key mediator of the physiological stimuli that modulate fiber-type plasticity in postembryonic development. Although myoblasts become fated to differentiate into distinct kinds of fibers early in development, the identities of regulatory proteins that determine embryonic fiber-type specification are still obscure. Here we show that the gene u-boot (ubo), a mutation in which disrupts the induction of embryonic slow-twitch fibers, encodes the zebrafish homolog of Blimp-1, a SET domain-containing transcription factor that promotes the terminal differentiation of B lymphocytes in mammals. Expression of ubo is induced by Hedgehog (Hh) signaling in prospective slow muscle precursors, and its activity alone is sufficient to direct slow-twitch fiber-specific development by naive myoblasts. Our data provide the first molecular insight into the mechanism by which a specific group of muscle precursors is driven along a distinct pathway of fiber-type differentiation in response to positional cues in the vertebrate embryo.

Animals↗
PubMed1988

Conduction studies in peripheral cat nerve using implanted electrodes: II. The effects of prolonged constriction on regeneration of crushed nerve fibers.

Arrays of chronically implanted electrodes were used to examine the time course of elongation and maturation of peripheral nerve fibers in the cat after crush of the tibial nerve in the proximal calf. Regeneration after crush alone was compared with crush 5 mm proximal to a tight constriction of the nerve. Regeneration was monitored by the progression of excitability along the electrode arrays on the tibial and plantar nerves. The sensitivity was sufficient to record the averaged activity in single nerve fibers allowing detection of the earliest regeneration. The diameters of the fastest regenerating fibers were estimated from the conduction velocity proximal to the site of crush. Both after crush alone, and after crush constriction, small myelinated fibers regenerated in front of large fibers. The rate of elongation after crush alone was 3.2 mm/day, whereas it was slower (P less than 0.02) distal to crush + constriction (2.2 mm/day). In both lesions, the extrapolated delay to onset of regeneration was 8 days. In observations up to 300 days after crush, maturation was delayed or impaired by the constriction, and the compound nerve action potential had a smaller amplitude and a dispersed shape. Transverse sections of nerves after crush + constriction showed a diminished number of large and an increased number of small fibers compared with crush alone, possibly due to persistent branching of regenerated fibers. After both crush alone and crush + constriction, regenerated fibers had similar g ratios, suggesting that myelination developed fully in fibers of diminished diameters.

Action Potentials↗
PubMed2002

Estimation of the conduction velocity distribution of human sensory nerve fibers.

A new method for estimating the distribution of conduction velocities (DCV) of peripheral nerve fibers has been developed. It also enables estimation of single nerve fiber action potential (SFAP), which agrees with the physiological knowledge. Two compound nerve action potentials (CAPs) elicited by electrical stimulation of a nerve bundle were recorded at different conduction distances. The distances between the stimulation and recording electrodes were measured on the skin surface along the nerve bundle. Starting with an arbitrary SFAP, the first estimated DCV was calculated from a CAP by the regularized non-negative least squares method. The next SFAP was then calculated by deconvolution of the other CAP and the estimated DCV. A lowpass filter with an appropriate cutoff frequency was used to obtain better conversion. The process was iterated until the CAP error defined as /CAP(calculated)-CAP/(2) was small enough. The conduction distances contained errors in measurement, especially in the distal segment, that distorted the estimated results. The Fibonacci search, therefore, was adopted to optimize the distance according to the CAP error. The accuracy of this method was demonstrated by a simulation study performed with two CAPs calculated from an arbitrary bimodal DCV and a biphasic SFAP to which a Gaussian white noise was added. The reliability of this method was checked in normal subjects by recording a pair of CAPs elicited by stimulation of the median nerve at the wrist and the elbow.

Action Potentials↗
PubMed1992

Gene expression in cotton (Gossypium hirsutum L.) fiber: cloning of the mRNAs.

Cotton, an important natural fiber, is a differentiated epidermal cell. The number of genes that are active in fiber cells is similar to those in leaf, ovule, or root tissues. Through differential screening of a fiber cDNA library, we isolated five cDNA clones that are preferentially expressed in fiber. One of the cDNA clones, pCKE6, corresponded to an abundant mRNA in fiber. Transcripts for E6 were detected throughout the development of the fiber. Immunoprecipitation of in vitro translation products and Western blot analysis of fiber proteins showed two polypeptides in the range of 30-32 kDa as the products of E6 mRNA. Sequence analysis and hybrid-selected RNA translation also suggest that E6 mRNAs encode two polypeptides. Concentrations of E6 mRNA and protein are highest during the late primary cell wall and early secondary cell wall synthesis stages. Sequence comparison of E6 with other known eukaryotic and prokaryotic genes reveals no significant homology (GenBank; December 1991). E6 or a homologous gene(s) is conserved in several members of Malvaceae as well as in one other fiber-producing plant, kapok, but is not found in several other plants examined or in Acetobacter xylinum. A genomic clone corresponding to pCKE6 was isolated, and the promoter element of the E6 gene was shown to direct the expression of a carrot extensin mRNA in a tissue-specific and developmentally regulated fashion in transgenic cotton plants.

Amino Acid Sequence↗
PubMed1977

Electron microscopic observations of the mechanisms of terminal club formation in transected spinal cord axons.

Following transection of spinal cords, axoplasmic flow occurred in the axons both proximal and distal to the transection. In the proximal axonal stump, the direction of flow was proximo-distal whereas in the distal axonal stump the direction of flow was disto-proximal. Thus the flows in transected axons were all directed toward the point of transection. Electron microscopic observation of the spinal cord tissue bordering at the cut ends of spinal cord stumps showed various structural changes in the axons and myelin sheaths of the transected fibers near the cut ends which interfered with the axoplasmic flow leading to the formation of the terminal clubs. Five prototypes of changes in axons and myelin sheaths near the cut ends of fibers are described and the mechanism of terminal club formation is discussed. It seemed that the terminal clubs within the transected spinal cord stumps rere of the axoplasmic flow toward the cut ends of the fibers, and (2) interference by structural changes which developed within individual fibers consequent to spinal cord injury.

Animals↗