The Anisotropic Elastic Properties of the Sarcolemma of the Frog Semitendinosus Muscle Fiber

Tension and curvature of the sarcolemmal tube of the frog muscle fiber were measured at different extensions and were used to calculate the anisotropic elastic properties of the sarcolemma. A model was derived to obtain the four parameters of the elasticity matrix of the sarcolemma. Sarcolemmal thickness was taken as 0.1 μm. Over the range of reversible sarcolemmal tube extension, the longitudinal elastic modulus E_L = 6.3 × 10⁷ dyn/cm², the circumferential modulus E_c = 0.88 × 10⁷ dyn/cm², the longitudinal Poisson's ratio σ_L = 1.2, and the circumferential Poisson's ratio σ_c = 0.18. At tubular rest length E_L = 1.2 × 10⁷ dyn/cm². The sarcolemma is less extensible in the longitudinal direction along the fiber axis than in the circumferential direction. It can be extended reversibly to 48% of its rest length, equivalent to extending the intact fiber from a sarcomere length of 3 μm to about 4.5 μm. The sarcolemma does not contribute to intact fiber tension at fiber sarcomere lengths <3 μm, and between 3 and 4 μm its contribution is about 20%. It also exerts a pressure on the myoplasm, which can be calculated by means of the model. The longitudinal elastic modulus of the whole fiber is 1 × 10⁵ dyn/cm² at a sarcomere length of 2.33 μm.     

Three Types of Single Voltage-Dependent Potassium Channels in the Sarcolemma of Frog Skeletal Muscle

Patch-clamp experiments in the sarcolemma of frog skeletal muscle evidenced the presence of three types of voltage-dependent single-channel K⁺ currents. According to their unitary conductance at a membrane voltage of +40 mV, we classified them as 16-, 13-, and 7-pS K⁺ channels. The 16-pS K⁺ channels are active close to a membrane voltage of −80 mV and they do not become inactivated during voltage pulses of 100 ms. Within 10 min after beginning the recording, these channels developed rundown with an exponential time course. The 13-pS K⁺ channels are active near −60 mV; upon a 100-ms depolarization, they exhibited inactivation with an approximate exponential time course. The 7-pS K⁺ channels were recorded at voltages positive to 0 mV. In patches containing all three types of K⁺ channels, the ensemble average currents resemble the kinetic properties of the macroscopic delayed rectifier K⁺ currents recorded in skeletal muscle and other tissues. In conclusion, the biophysical properties of unitary K⁺ currents suggest that these single-channel K⁺ currents may underlie the macroscopic delayed K⁺ currents in frog skeletal muscle fibers. In addition, since the 16- and 13-pS channels were more frequently recorded, both are the main contributors to the delayed K⁺ currents.     

Pharmacological Properties of Glycine Transport in the Frog Retina

The high-affinity glycine transport in neurons and glial cells is the primary means for inactivating synaptic glycine. Two different glycine transporter genes, Glyt-1 and Glyt-2, have been cloned. Glyt-1 has been reported to occur in the retina, but there is no evidence for expression of the Glyt-2 transporter. We have pharmacologically characterized glycine transport in the frog retina. 3H-Glycine uptake in the retina was insensitive to modulation by phorbol esters or changes in cAMP levels, and was partially inhibited by sarcosine. Differential sensitivity of glycine transport to sarcosine was exhibited by synaptosomal fractions from the inner and outer plexiform layers of the frog retina. The Na+ Hill coefficient of glycine uptake was 2.0, as has been reported for Glyt-2. In addition, amoxapine, a specific inhibitor of the Glyt-2a isoform, reduced by 60% glycine uptake by P2 synaptosomal fraction. Our results indicate the presence of different glycine transporter isoforms in the frog retina, acting mainly through the classical inhibitory glycine system.     

Nerve Stimulation and Electrical Properties of Frog Skin

The suitability of frog skin glands as a model for the study of secretory mechanisms in exocrine glands was explored. Periodic voltage clamp was used to determine continually the short-circuit current, chord conductance, and electromotive force of frog skin during neural and pharmacological activation of the skin glands. Both the chord conductance and the short-circuit current increased with glandular activation; the temporal dissociation of these increases suggests that there are at least two separate components to the secretory response. The sensitivity of the secretory electrical changes to changes in the ionic composition of the bathing solutions supports the notion of electrogenic chloride active transport as being basic to the activity of the exocrine glands.     

Preparation and Properties of an Inhibitory Extract from Frog Virus 3 Particles

The structural constituents of the frog virus 3 particle were solubilized by treatment with a nonionic detergent followed by the addition of a high salt concentration. This soluble viral extract (SVE) inhibits host nucleic acid synthesis. Its activity on RNA synthesis was studied in KB cells and found to be dependent on the presence of DEAE dextran. Inactivation of the inhibitory properties of SVE were obtained by trypsin digestion, treatment with urea, or heat denaturation. Neutralization of the activity of SVE was obtained by anti-frog virus 3 serum but not by anti-BHK serum. In vitro a complex may be formed between polynucleotides and the inhibitor indicating a possible mechanism for vivo inhibition.     

Sarcolemma blebs and cell damage in mammalian skeletal muscle

Plasma membrane blebs are an early sign of cellular damage in isolated cells. Phenazine methosulphate (PMS) triggers the production of conspicuous and characteristic sarcolemma blebs in mouse diaphragm skeletal muscle incubated in vitro and also causes severe myofilament damage. It is suggested that PMS activates transmembrane NAD(P)H dehydrogenases and, in turn, a modification of sulphydryl groups of the cytoskeleton, thereby permitting bleb formation in contracting cells.     

Uniform Action Potential Repolarization within the Sarcolemma of In Situ Ventricular Cardiomyocytes

Previous studies have speculated, based on indirect evidence, that the action potential at the transverse (t)-tubules is longer than at the surface membrane in mammalian ventricular cardiomyocytes. To date, no technique has enabled recording of electrical activity selectively at the t-tubules to directly examine this hypothesis. We used confocal line-scan imaging in conjunction with the fast response voltage-sensitive dyes ANNINE-6 and ANNINE-6plus to resolve action potential-related changes in fractional dye fluorescence (ΔF/F) at the t-tubule and surface membranes of in situ mouse ventricular cardiomyocytes. Peak ΔF/F during action potential phase 0 depolarization averaged −21% for both dyes. The shape and time course of optical action potentials measured with the water-soluble ANNINE-6plus were indistinguishable from those of action potentials recorded with intracellular microelectrodes in the absence of the dye. In contrast, optical action potentials measured with the water-insoluble ANNINE-6 were significantly prolonged compared to the electrical recordings obtained from dye-free hearts, suggesting electrophysiological effects of ANNINE-6 and/or its solvents. With either dye, the kinetics of action potential-dependent changes in ΔF/F during repolarization were found to be similar at the t-tubular and surface membranes. This study provides what to our knowledge are the first direct measurements of t-tubule electrical activity in ventricular cardiomyocytes, which support the concept that action potential duration is uniform throughout the sarcolemma of individual cells.     

Photosensitivity of the Frog Iris

The absorption of quanta by rhodopsin leads to the contraction of frog iris muscle. The contractions reach a maximum after about 8 sec. in the light. When the light is turned off the irises relax exponentially with a half-time of about 6 sec. Membrane polarization is not necessary for the response but calcium movement and membrane permeability changes probably are. The response is not mediated by acetylcholine or epinephrine. The curves of log It vs. log t for constant response amplitude bend progressively upward away from a unit slope line at short times as larger response criteria are used because (a) light influences tension development over longer times and (b) the higher intensity, shorter duration flashes are less effective.     

Protein Components of the Purified Sodium Channel from Rat Skeletal Muscle Sarcolemma

Abstract: Sensitive detection systems have been used to study the protein components of the sodium channel purified from rat skeletal muscle sarcolemma. This functional, purified sodium channel contains at least three subunits on 7–20% gradient sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis: a large glycoprotein which migrates anomalously in the high-molecular-weight range, a 45,000 molecular weight polypeptide, and a third protein often seen as a doublet at 38,000. The large glycoprotein runs as a diffuse band and stains very poorly with Coomassie blue, but is adequately visualized with silver staining or iodination followed by autoradiography. This glycoprotein exhibits anomalous electrophoretic behavior in SDS-polyacrylamide gels. The apparent molecular weight of the center of the band varies from ～230,000 on 13% acrylamide gels to ～130,000 on 5% gels; on 7–20% gradient gels a value of 160,000 is found. Plots of relative migration versus gel concentration suggest an unusually high apparent free solution mobility. Lectin binding to purified channel peptides separated by gel electrophoresis indicates that the large glycoprotein is the only subunit that binds either concanavalin A or wheat germ agglutinin, and this component has high binding capacity for both lectins. The smaller channel components run consistently at 45,000 and 38,000 molecular weight in a variety of gel systems and do not appear to be glycosylated.     

Comparative Mechanical Properties and Histology of Bone

Different bone tissues differ in their amounts of porosity,mineralization,reconstruction, and preferred orientation. Allthese have important effects on mechanical properties. Veryporous, cancellous bone is always weaker and morecompliant thancompact bone on a weight for weight basis, yet it occurs inplaceswhere its energyabsorbing ability, or its low density,is advantageous. Bonevaries considerably in its mineralization,and such variations have quite disproportionate effects on mechanicalproperties. These variations can be shown to be adaptive. Inparticular, there must always be a compromise between stiffnessandresistanceto fracture; these two properties run contrary to each other.The reason for secondary remodeling is an unresolved problem,though in a few places the role of such remodeling in changingthe grain of the bone is clearly mechanically adaptive. Themechanical properties of non-mammalian bone are obscure, andas the histology of such bone is often quite different fromthat of mammalian bone, we are no doubt in for some surpriseswhen the mechanical properties ofnonmammalian bone are discovered.     

电渗析法进行胱氨酸母液脱盐的研究

猪毛酸解提取胱氨酸后的母液中含有十七种氨基酸。本文报道了采用我校由辐射法制备的高性能离子交换膜（ＨＦ－１及ＨＦ－２）,通过电渗析技术对母液进行脱盐并制得混合氨基酸。该技术已运转近一年,脱盐率＞９５．５％,氨基酸中人体必须氨基酸达２０％以上。     

Mechanical Properties of the Rhizome of Arundo donax L.

Abstract: The mechanical properties of rhizome segments of Arundo donax L. were studied in three dimensions: longitudinal (X), transverse-vertical (Y), transverse-horizontal (Z). Tensile, cyclic loading and torsional tests demonstrate that the distinct anisotropy found in the hollow stems is less pronounced in the rhizome. Morphological and anatomical examinations suggest that the mechanical anisotropy of the stem is caused by the arrangement parallel to the stem of the vascular bundles and sclerenchymatous fibres, embedded in lignified parenchyma. Anatomical inhomogeneity is less pronounced in the rhizome due to the short internode lengths, and predominance of nodal regions, where sclerenchymatous fibres form a complex three-dimensional arrangement embedded in unlignified starch-storing parenchyma. Cyclic loading experiments indicate viscoelastic behaviour of the rhizomatous tissues under tensile stress. Additionally, viscoelastic behaviour under torsional stress was studied. Mechanical behaviour of the rhizome under tension up to fracture is discussed with regard to the fracture surfaces, analysed by SEM.     

Controlling the Three-Dimensional Printing Mechanical Properties of Nostoc Sphaeroides System

The main purpose of this paper is to explore the opportunities for fresh Nostoc sphaeroides (N. sphaeroides) to be applied to 3D food printing. N. sphaeroides is rich in nutrients and its paste possesses shear thinning properties. It was found the product obtained by 3D food printing with fresh N. sphaeroides had poor printability and was easy to collapse. In this study, we compared the addition of different potato starch (2%, 4%, 6% and 8%) to the characteristics of 3D printing of the N. sphaeroides gel system. The results obtained from the rheological analysis showed that the 6% potato starch added to of N. sphaeroides gel can be utilized for 3D food printing. The addition of potato starch increased the viscosity of the mixture so the printed lines were not easily broken, and the “self-supporting ability” of the material itself was enhanced to maintain a good shape without collapse. Texture profile analysis also showed that the 6% starch added printed product had the best gumminess parameter. In order to get a better printed product, the effects of printing parameters (nozzle diameter (Dn), extrusion rate (Vd) and nozzle moving speed (Vn)) on material printing performance and product formability was tested. When Dn, Vd, Vn were = 1.2 mm, 20 mm³/s, 25 mm/s, respectively, the printed product was having similar to the target product, with less breakage and less the changing of shape. Overall results show that 3D printing technology is a rising method for producing N. sphaeroides-based new products.

     

Fluctuation Simulations and the Calculation of Mechanical Partial Molar Properties

Abstract

A method for the direct calculation of partial molar volumes, energies, and enthalpies in multicomponent mixtures in which all species have finite concentrations is presented. The approach, which is based on fluctuation theory, allows the simultaneous determination of the properties of all components in the mixture. The advantages and limitations of the method are illustrated through the (N, U, V) molecular dynamics calculation of the mechanical partial molar properties of two binary Lennard-Jones mixtures.