Self‐Actuating Electrocaloric Cooling Fibers

Solid‐state cooling fibers comprising an electrocaloric polymer, poly(vinylidene fluoride‐trifluoroethylene‐chlorofluoroethylene) terpolymer, spray‐coated on a conductive fiber core electrode, and a coaxially coated single‐walled carbon nanotubes outer electrode are reported. The fiber coolers can be less than 160 µm thin and more than 8 cm long. Measured cooling ΔT of the EC fibers is 0.7 °C at an electric field of 100 V µm^?1 applied between the electrodes. The fiber coolers are flexible; 2000 cycles of repeated bending to a 2.5 mm curvature radius do not significantly degrade the cooling ΔT. Self‐actuated bending of the fibers is observed during the EC operation, which allows the EC fibers to move heat from one location to another without any additional driving mechanisms such as electromagnetic motors, pumps, or electrostatic actuation that are commonly used in conventional coolers. The self‐actuating EC fibers represent the first ever active cooler in a thin fiber form factor.     

Controlled differentiation of myoblast cells into fast and slow muscle fibers

Skeletal muscles are classified into fast and slow muscles, which are characterized by the expression of fast-type myosin heavy chains (fMyHCs) or slow-type myosin heavy chains (sMyHCs), respectively. However, the mechanism of subtype determination during muscle fiber regeneration is unclear. We have analyzed whether the type of muscle is determined in the myoblast cells or is controlled by the environment in which the muscle fibers are formed from myoblast cells. When myoblast cells from 7-day-old chick embryo were cultured and formed into muscle fibers, more than half of the fibers produced only fMyHCs, and the remaining fibers produced both fMyHCs and sMyHCs. However, when myoblast cells were cultured in medium supplemented with a small amount of slow muscle extract, the expression of sMyHCs in muscle fibers increased, whereas the expression of fMyHCs increased in the group supplemented with fast muscle extract compared with the control group. The same results were obtained when cloned mouse myoblast cells (C₂C₁₂ cells) were cultured and formed into muscle fibers. The data presented here thus show that the subtype differentiation of muscle fiber is controlled by the environment in which the muscle fiber forms. This work was funded by the Sasakawa Scientific Research Grant of the Japan Science Society.     

Histochemical and molecular determination of fiber types in chemically skinned single equine skeletal muscle fibers

Until now, there has been no reliable method for histochemical determination of fiber types of single skinned muscle fibers. The major problem arises from the fact that most histochemical techniques use cross-sections of a large group of fibers and compare a given fiber with those surrounding it. This is not possible with a single skinned fiber which has been separated from a bundle to be used for mechanical analysis. A further problem is that the skinning procedure itself may alter the staining pattern. We have developed a procedure by which multiple cross-sections of single skinned fibers can be exposed to various histochemical reactions and the staining patterns compared on the same slide to those of frozen muscle and skinned bundles. By this procedure, three fiber types were distinguished by both Ca2+-ATPase and SDH reactions. The fiber typings determined from both enzyme systems correlated well with each other. Although we were able to differentiate only between slow and fast fibers by SDS-PAGE, these results corroborated the histochemical classification. This procedure will clearly be useful in skinned single muscle fiber mechanics experiments performed to determine functional differences among fiber types.     

不同强度运动对骨骼肌纤维MHC亚型转化及CaN/NFATc1信号通路的影响

目的：研究不同强度运动对骨骼肌纤维MHC亚型转化及钙调神经磷酸酶（CaN）/活化T细胞核因子1（NFATc1）信号通路的影响。方法：雄性SD大鼠（2月龄）24只,随机分为3组（n=8）：正常对照组（NC）、中等强度组（ME）、大强度组（HE）,进行8周跑台训练。采用ATP酶染色法测定I、Ⅱ型肌纤维,凝胶电泳技术分离肌球蛋白重链（MHC）亚型,比色法测定骨骼肌中CaN活性,免疫印迹技术测定骨骼肌NFATc1蛋白含量。结果：①肌纤维密度变化：股四头肌ME组I、Ⅱ型纤维数密度均显著增加（P<0.05）,HE组仅Ⅱ型纤维面密度显著增加（P<0.05）;比目鱼肌HE、ME组I型纤维数密度均显著增加（P<0.05）;②肌纤维MHC亚型百分比变化：股四头肌ME组MHCI、Ⅱa百分比升高（P<0.05）,而MHCⅡb百分比降低（P<0.05）;比目鱼肌MHCI百分比升高,MHCⅡa、Ⅱb百分比降低;③ME组大鼠CaN活性、NFAT1蛋白含量均显著升高（P<0.05）。结论：大、中等强度运动可诱导骨骼肌MHC快型向慢型转化,同时伴随肌纤维亚型变化骨骼肌中CaN活性增加、NFATc1蛋白表达增加。     

PRC1‐labeled microtubule bundles and kinetochore pairs show one‐to‐one association in metaphase

In the mitotic spindle, kinetochore microtubules form k‐fibers, whereas overlap or interpolar microtubules form antiparallel arrays containing the cross‐linker protein regulator of cytokinesis 1 (PRC1). We have recently shown that an overlap bundle, termed bridging fiber, links outermost sister k‐fibers. However, the relationship between overlap bundles and k‐fibers throughout the spindle remained unknown. Here, we show that in a metaphase spindle more than 90% of overlap bundles act as a bridge between sister k‐fibers. We found that the number of PRC1‐GFP‐labeled bundles per spindle is nearly the same as the number of kinetochore pairs. Live‐cell imaging revealed that kinetochore movement in the equatorial plane of the spindle is highly correlated with the movement of the coupled PRC1‐GFP‐labeled fiber, whereas the correlation with other fibers decreases with increasing distance. Analysis of endogenous PRC1 localization confirmed the results obtained with PRC1‐GFP. PRC1 knockdown reduced the bridging fiber thickness and interkinetochore distance throughout the spindle, suggesting a function of PRC1 in bridging microtubule organization and force balance in the metaphase spindle.     

Mitochondrial DNA deletion mutations are concomitant with ragged red regions of individual, aged muscle fibers: analysis by laser-capture microdissection

Laser-capture microdissection was coupled with PCR to define the mitochondrial genotype of aged muscle fibers exhibiting mitochondrial enzymatic abnormalities. These electron transport system (ETS) abnormalities accumulate with age, are localized segmentally along muscle fibers, are associated with fiber atrophy and may contribute to age-related fiber loss. DNA extracted from single, 10 µm thick, ETS abnormal muscle fibers, as well as sections from normal fibers, served as templates for PCR-based deletion analysis. Large mitochondrial (mt) DNA deletion mutations (4.4–9.7 kb) were detected in all 29 ETS abnormal fibers analyzed. Deleted mtDNA genomes were detected only in the regions of the fibers with ETS abnormalities; adjacent phenotypically normal portions of the same fiber contained wild-type mtDNA. In addition, identical mtDNA deletion mutations were found within different sections of the same abnormal region. These findings demonstrate that large deletion mutations are associated with ETS abnormalities in aged rat muscle and that, within a fiber, deletion mutations are clonal. The displacement of wild-type mtDNAs with mutant mtDNAs results in concomitant mitochondrial enzymatic abnormalities, fiber atrophy and fiber breakage.     

Anti-myosin heavy chain monoclonal antibodies reveal two IIB (fast) fiber subtypes

Indirect immunofluorescence analysis of different rat skeletal muscles using anti-myosin heavy chain (MHC) monoclonal antibodies (MAb) revealed the presence of two immunologically distinct kinds of fibers within the IIB fibers, histochemically identified by myosin ATPase staining. Some IIB fibers (designated here as IIB1) were unreactive with one anti-fast MHC MAb, whereas they did react with another anti-fast MHC MAb; other IIB fibers (designated here as IIB2) reacted with both anti-fast MAbs. Neither of the two IIB fiber subtypes was significantly reactive with a neonatal MHC MAb. The number of each IIB fiber subtype was age-dependent, at least in the plantaris muscle. IIB1 fibers were observed only in the superficial portion of the plantaris and gastrocnemius muscle. The ratio of IIB1:IIB2 fibers was about the same throughout the extensor digitorum longus and extraocular muscles. Therefore, the two kinds of IIB fibers here observed have a different myosin heavy chain content. On the basis of their specific immunoreactivities, we suggest that IIB1 fibers contain the previously described MHCB. IIB2 fibers contain either a unique new MHC isoform or a mixture of at least two MHC, possibly composed of the MHCB and either the previously described MHCA or a new MHC isoform.     

The pattern of cell wall deterioration in lignocellulose fibers throughout enzymatic cellulose hydrolysis

Cell wall deterioration throughout enzymatic hydrolysis of cellulosic biomass is greatly affected by the chemical composition and the ultrastructure of the fiber cell wall. The resulting pattern of cell wall deterioration will reveal information on cellulose activity throughout enzymatic hydrolysis. This study investigates the progression and morphological changes in lignocellulose fibers throughout enzymatic hydrolysis, using (transmission electron microscopy) TEM and field emission scanning electron microscopy (FE‐SEM). Softwood thermo‐mechanical pulp (STMP) and softwood bleached kraft pulp (SBKP), lignocellulose substrates containing almost all the original fiber composition, and with lignin and some hemicellulose removed, respectively, was compared for morphology changes throughout hydrolysis. The difference of conversion between STMP and SBKP after 48 h of enzymatic hydrolysis is 11 and 88%, respectively. TEM images revealed an even fiber cell wall cross section density, with uneven middle lamella coverage in STMP fibers. SKBP fibers exhibited some spaces between cell wall and lamella layers due to the removal of lignin and some hemicellulose. After 1 h hydrolysis in SBKP fibers, there were more changes in the fiber cross‐sectional area than after 10 h hydrolysis in STMP fibers. Cell wall degradation was uneven, and originated in accessible cellulose throughout the fiber cell wall. FE‐SEM images illustrated more morphology changes in SBKP fibers than STMP fibers. Enzymatic action of STMP fiber resulted in a smoother fiber surface, along with fiber peeling and the formation of ribbon‐disjunction layers. SBKP fibers exhibited structural changes such as fiber erosion, fiber cutting, and fiber splitting throughout enzymatic hydrolysis. © 2012 American Institute of Chemical Engineers Biotechnol. Prog., 2012     

麦秸秆/高密度聚乙烯（HDPE）复合材料中纤维分散性的描述模型

麦秸秆纤维作为一种重要生物质资源已被广泛应用于热塑性复合材料中。纤维在复合材料中的分散性是影响复合材料力学性能的重要因素之一,而目前对其定量化的描述和分析方法仍存在一定不足。本研究基于实验获得的纤维尺寸的统计分布规律,利用随机生成算法模拟纤维在复合材料中的分布;构建描述纤维分散性的指标:分散度,单个纤维数和接触纤维数;统计分析纤维含量、纤维大小对分散性指标影响。结果表明单个纤维数随纤维含量增加而增加,但其增量随纤维含量的增加而降低,降低规律符合三次函数。纤维接触数随纤维含量增加,增加规律符合二次函数,亦符合理论估计。纤维大小影响单个纤维数和接触纤维数的增加幅度,但不影响单个纤维数的百分比。分散度随纤维含量的增加呈线性下降规律。纤维分散性的定量化描述为进一步的复合材料性能分析和建模提供了量化指标。     

Myofibrillar ATPase histochemistry of rat skeletal muscles: a "two-dimensional" quantitative approach

In histochemical investigations of skeletal muscle, the fibers are commonly classified into three types according to their staining for myofibrillar ATPase (mATPase). In serial sections of skeletal muscles from normal Wistar rats, we compared two common staining methods for mATPase: (a) an ac-ATPase technique, with pre-incubation at pH 4.7, and (b) a fixed alk-ATPase technique, using treatment with 5% paraformaldehyde followed by pre-incubation at pH 10.4. In addition, the same fibers were stained in subsequent serial sections for succinate dehydrogenase (SDH) activity. Staining intensities were objectively evaluated by microphotometric measurements of optical density. Combining both mATPase methods in consecutive serial sections ("two-dimensional approach") led to the identification of four distinct clusters of fibers: Types I, IIA, and two subgroups of Type IIB, as separated by their staining densities for fixed alk-ATPase (IIBd dark, IIBm moderate). The mean intensity of SDH staining per fiber type, as measured in the central core of the fibers, was ranked such that IIA greater than I greater than IIBd greater than IIBm. The analyzed muscles (tibialis anterior, biceps brachii) were markedly heterogeneous with respect to the topographic distribution of different fiber types. In comparison to other muscle portions, the regions containing Type I fibers ("red" portions) showed a higher IIBd vs IIBm ratio and more intense SDH staining for either subtype of the IIB fibers. The IIBd fibers probably correspond to the Type 2X fibers of Schiaffino et al.     

Type 1, 2A, and 2B myosin heavy chain electrophoretic analysis of rat muscle fibers

Mammalian skeletal muscles are mixture of three type of fibers: type 1, type 2A, and type 2B fibers. Immunological studies and proteolytic analysis of myosin heavy chains from the three type of fibers have demonstrated the presence of distinct myosin isoforms. By using typed single muscle fibers and improving an electrophoretic method we are able to resolve three distinct polypeptides which are demonstrate to correspond to type 1, 2A and 2B myosin heavy chain isoforms by using specific monoclonal antibodies. The analysis of single muscle fibers shows that different myosin heavy chain isoforms are frequently coexpressed in the same muscle fiber.     

Magnetic field of a single muscle fiber. First measurements and a core conductor model.

We present the first measurements of the magnetic field from a single muscle fiber of the frog gastrocnemius, obtained by using a toroidal pickup coil coupled to a room-temperature, low-noise amplifier. The axial currents associated with the magnetic fields of single fibers were biphasic and had peak-to-peak amplitudes ranging between 50 and 100 nA, depending primarily on the fiber radius. With an intracellular microelectrode, we measured the action potential of the same fiber, which allowed us to determine that the intracellular conductivity of the muscle fiber in the core conductor approximation was 0.20 +/- 0.09 S/m. Similarly, we found that the effective membrane capacitance was 0.030 +/- 0.011 F/m2. These results were not significantly affected by the anisotropic conductivity of the muscle bundle. We demonstrate how our magnetic technique can be used to determine the transmembrane action potential without penetrating the membrane with a microelectrode, thereby offering a reliable, stable, and atraumatic method for studying contracting muscle fibers.     

In vivo testing of a bioresorbable phosphate‐based optical fiber

Optical fibers have recently attracted a noticeable interest for biomedical applications because they provide a minimally invasive method for in vivo sensing, imaging techniques, deep‐tissue photodynamic therapy or optogenetics. The silica optical fibers are the most commonly used because they offer excellent optical properties, and they are readily available at a reasonable price. The fused silica is a biocompatible material, but it is not bioresorbable so it does not decompose in the body and the fibers must be ex‐planted after in vivo use and their fragments can present a considerable risk to the patient when the fiber breaks. In contrast, optical fibers made of phosphate glasses can bring many benefits because such glasses exhibit good transparency in ultraviolet‐visible and near‐infrared regions, and their solubility in water can be tailored by changing the chemical composition. The bioresorbability and toxicity of phosphate glass–based optical fibers were tested in vivo on male laboratory rats for the first time. The fiber was spliced together with a standard graded‐index multi‐mode fiber pigtail and an optical probe for in vitro pH measurement was prepared by the immobilization of a fluorescent dye on the fiber tip by a sol‐gel method to demonstrate applicability and compatibility of the fiber with common fiber optics.      

Chemically Mediated Transmission at a Giant Fiber Synapse in the Central Nervous System of a Vertebrate

The hatchetfish, Gasteropelecus, possesses large pectoral fin adductor muscles whose simultaneous contraction enables the fish to dart upwards at the approach of a predator. These muscles can be excited by either Mauthner fiber. In the medulla, each Mauthner fiber forms axo-axonic synapses on four "giant fibers," two on each side of the midline. Each pair of giant fibers innervates ipsilateral motoneurons controlling the pectoral fin adductor muscles. Mauthner fibers and giant fibers can be penetrated simultaneously by microelectrodes close to the synapses between them. Electrophysiological evidence indicates that transmission from Mauthner to giant fiber is chemically mediated. Under some conditions miniature postsynaptic potentials (PSP's) are observed, suggesting quantal release of transmitter. However, relatively high frequency stimulation reduces PSP amplitude below that of the miniature potentials, but causes no complete failures of PSP's. Thus quantum size is reduced or postsynaptic membrane is desensitized. Ramp currents in Mauthner fibers that rise too slowly to initiate spikes can evoke responses in giant fibers that appear to be asynchronous PSP's. Probably both spikes and ramp currents act on the same secretory mechanism. A single Mauthner fiber spike is followed by prolonged depression of transmission; also PSP amplitude is little affected by current pulses that markedly alter presynaptic spike height. These findings suggest that even a small spike releases most of an immediately available store of transmitter. If so, the probability of release by a single spike is high for any quantum of transmitter within this store.     

Peripheral Interactions among Single Papilla Inputs to Gustatory Nerve Fibers

Recordings were made from single fibers of the rat chorda tympani nerve while the peripheral receptor fields were mapped using a stimulator developed to stimulate single fungiform papillae which in the rat contain a solitary taste bud. The results indicate that several fungiform papillae may supply input to a single fiber, and the most sensitive papilla of these provided, on the average, about one-half of the response of that fiber to stimulation of the entire tongue. The magnitude of the response to each concentration of stimulus and the shape of the concentration-response curves differ among papillae innervated by the same fiber. If one of the papillae supplying input to the fiber was stimulated individually with NaCl solution, application of this stimulus to the tongue surface surrounding the isolated papilla resulted in enhancement of the fiber response. If the papilla was stimulated with NaCl and potassium benzoate solution was applied to the surround, a depression of the response occurred. The excitatory input of the cationic stimuli and the depressing influence of the anionic stimuli interacted to determine the resultant steady-state impulse frequency of the single afferent fiber. A hypothetical model involving the summation of generator currents along the unmyelinated terminals of the single afferent neuron is presented as a speculative explanation of the integration of inputs from several receptors innervated by the same single fiber.     

Receptive fields and gustatory responsiveness of frog glossopharyngeal nerve. A single fiber analysis

Receptive fields and responsiveness of single fibers of the glossopharyngeal (IXth) nerve were investigated using electrical, gustatory (NaCl, quinine HCl, acetic acid, water, sucrose, and CaCl2), thermal, and mechanical stimulation of the single fungiform papillae distributed on the dorsal tongue surface in frogs. 172 single fibers were isolated. 58% of these fibers (99/172) were responsive to at least one of the gustatory stimuli (taste fibers), and the remaining 42% (73/172) were responsive only to touch (touch fibers). The number of papillae innervated by a single fiber (receptive field) was between 1 and 17 for taste fibers and between 1 and 10 for touch fibers. The mean receptive field of taste fibers (X = 6.6, n = 99) was significantly larger than that of touch fibers (X = 3.6, n = 73) (two-tailed t test, P less than 0.001). In experiments with natural stimulation of single fungiform papillae, it was found that every branch of a single fiber has a similar responsiveness. Taste fibers were classified into 14 types (Type N, Q, A, NA, NCa, NCaA, NCaW, NCaAW, NCaWS, NQ, NQA, NQAS, NQWarm, Multiple) on the basis of their responses to gustatory and thermal stimuli. The time course of the response in taste fibers was found to be characteristic of their types. For example, the fibers belonging to Type NQA showed phasic responses, those in Type NCa showed tonic responses, etc. These results indicate that there are several groups of fibers in the frog IXth nerve and that every branch of an individual fiber has a similar responsiveness to the parent fiber.     

Coexistence of fast and slow types of myosin light chains in a single fiber of rat soleus muscle

Single muscle fibers were isolated from soleus and extensor digitorum longus muscle of adult rats. The muscle fiber type of single fibers was determined physiologically by the skinned fiber method according to the sensitivity to strontium (Sr) ions. The fiber type of single fibers was contrasted to the pattern of myosin light chains analyzed by one and two dimensional gel-electrophoreses. All the type 2 fibers isolated from soleus muscle contained both fast and slow types of myosin light chains.     

Morphology of the core fibrous layer of the cetacean tail fluke

The cetacean tail fluke blades are not supported by any vertebral elements. Instead, the majority of the blades are composed of a densely packed collagenous fiber matrix known as the core layer. Fluke blades from six species of odontocete cetaceans were examined to compare the morphology and orientation of fibers at different locations along the spanwise and chordwise fluke blade axes. The general fiber morphology was consistent with a three‐dimensional structure comprised of two‐dimensional sheets of fibers aligned tightly in a laminated configuration along the spanwise axis. The laminated configuration of the fluke blades helps to maintain spanwise rigidity while allowing partial flexibility during swimming. When viewing the chordwise sectional face at the leading edge and mid‐chord regions, fibers displayed a crossing pattern. This configuration relates to bending and structural support of the fluke blade. The trailing edge core was found to have parallel fibers arranged more dorso‐ventrally. The fiber morphology of the fluke blades was dorso‐ventrally symmetrical and similar in all species except the pygmy sperm whale (Kogia breviceps), which was found to have additional core layer fiber bundles running along the span of the fluke blade. These additional fibers may increase stiffness of the structure by resisting tension along their long spanwise axis.