Rayleigh-Taylor instability in magnetohydrodynamics with finite resistivity in a horizontal magnetic field

Recent studies have revealed the significant influence of finite resistivity on high-energy-density plasmas, contrary to the previous findings of Jukes [J. Fluid Mech. 16, 177 (1963)0022-112010.1017/S0022112063000677]. This paper reexamines Jukes' theory in the context of magneto-Rayleigh-Taylor instability in magnetohydrodynamics with finite resistivity represented by η. The inadequacy of Jukes' approach due to an erroneous boundary condition is demonstrated, and it is shown that although the theory provides some physical insights, it fails to capture crucial features. The dispersion relation proposed in this study highlights that larger growth rates tend to diffuse the magnetic field rapidly, negating its suppressive effect. Moreover, the Atwood number has a significant influence on the growth-rate curves' shape, which differs from those of viscous or elastic flows and ideal magnetohydrodynamics. Additionally, long wavelengths grow proportionally to η^{1/3}, while α indicating growth rates behaves classically when the magnetic field is entirely diffused.

[Diagnosis and treatment of 18 cases of Chiari malformation with hoarseness]

Objective: To investigate the diagnosis and treatment of Chiari malformation patients with hoarseness and other otorhinolaryngological symptoms. Methods: The clinical data of 18 patients of Chiari malformation with hoarseness were retrospectively collected, which was composed of 5 men and 13 women, aged 3-71 with median age of 52. All the patients were admitted to the Affiliated Hospital of Qingdao University from January 1989 to January 2020. All patients underwent brain MRI and laryngoscopy. The patient's symptoms and first diagnosis department, diagnosis time, total course of disease, hoarseness course, diagnosis and treatment, and postoperative recovery time were summarized. Follow-up time was 3-16 years, with median follow-up time of 6.5 years. Descriptive methods were used for analysis. Results: The first visit departments of 18 patients included neurology (9 cases), otorhinolaryngology head and neck surgery (5 cases), pediatrics (2 cases), orthopedics (1 case) and respiratory department (1 case). Except for the 7 cases in neurology department, the other 11 patients were not diagnosed in time. The disease duration of 18 patients with Chiari malformation ranged from 2 months to 5 years, and hoarseness was present from 20 days to 5 years. After diagnosis, 9 patients underwent posterior fossa decompression surgery, and 1 of them underwent syrinx drainage at the same time. The symptoms of 8 cases improved significantly after operation, with the improvement time from 1 to 30 days. In addition, 9 patients chose conservative treatment, among whom 8 had no improvement in symptoms and 6 progressed. Conclusions: Posterior fossa decompression is an effective treatment for Chiari malformation, and the prognosis is good. Timely diagnosis and treatment can improve the prognosis of patients.

Linear analysis of Rayleigh-Taylor instability in viscoelastic materials

Rayleigh-Taylor instability (RTI) has become a powerful tool for determining the mechanical properties of materials under extreme conditions. In this paper, we first present the exact and approximate linear dispersion relations for RTI in viscoelastic materials based on the Maxwell and Kelvin-Voigt models. The approximate dispersion relation produces good predictions of growth rates in comparison with the exact one. The motion of the interface in Maxwell flow is mainly controlled by viscosity and elasticity dominates this behavior in Kelvin-Voigt flow. Since elasticity plays a distinct role from viscosity, cutoff wavelengths arise only in Kelvin-Voigt flow. The variation of the maximum growth rates and their corresponding wave numbers are also carefully studied. For both types of materials, viscosity suppresses the growth of instability, while elasticity speeds it up. This is at odds with the well-known understanding that elasticity suppresses hydrodynamic instabilities. The dependence of the maximum growth rate on slab thickness is also investigated for RTI in both types of flow, since the metal slab as a pusher has been extensively employed in high-energy-density physics. The model presented here allows study of more realistic situations by considering convergent effects and shock wave interactions, for the traditional potential flow theory is not suitable. To summary, it is able to provide guidances for future experimental designs for studies of materials under high strain and high strain rate conditions, as well as allow us to study RTI theoretically in more complicated conditions.

Three-dimensional viscous Rayleigh-Taylor instability at the cylindrical interface

In this paper, the rotational part of the disturbance flow field caused by viscous Rayleigh-Taylor instability (RTI) at the cylindrical interface is considered, and the most unstable mode is revealed to be three-dimensional for interfaces of small radii R. With an increase in R, the azimuthal wave number of the most unstable mode increases step by step, and the corresponding axial wave number increases as well at each step of the azimuthal wave number. When the amplitude of the wave-number vector is much larger or much smaller than 1/R, the cylindrical RTI is close to the semi-infinite planar viscous RTI limit or the finite-thickness creeping-flow RTI limit, respectively. The effect of the viscosity ratio is double-edged; it may enhance or suppress the cylindrical RTI, depending on R and the amplitude range of the wave-number vector.

Viscous Rayleigh-Taylor and Richtmyer-Meshkov instabilities in the presence of a horizontal magnetic field

We first derive the exact dispersion relation for viscous Rayleigh-Taylor instability in the presence of a horizontal magnetic field using a decomposition method, and we find that the horizontal magnetic field contributes to the generation of vorticity inside the flow, thereby further distorting the velocity field. This differs from the previous view of the horizontal magnetic field behaving as a surface-tension-like force that does not produce any vorticity in inviscid flow. Vorticity transport is also investigated. The well-known approximate dispersion relation yields growth rates based on an irrotational approximation with a maximum error of 19% in comparison with the exact rates. Furthermore, we investigate the physics of the viscous Richtmyer-Meshkov instability in the presence of a magnetic field, and we find that the presence of the magnetic field leads to the generation of more eigenvalues, thereby modifying the motion of the interface. Comparisons confirm that the viscosity and magnetic field both play fundamental roles in interface behavior, and it is clarified that the behaviors of the interface for viscous Richtmyer-Meshkov instability become in agreement with the numerical simulations. The dependences of the eigenvalues on the viscosities and densities of the fluids, as well as on the magnetic field, are also discussed. Finally, we analyze the evolution of the decay modes to investigate the rotationality of the velocity fields.

mTOR-mediated podocyte hypertrophy regulates glomerular integrity in mice and humans

The cellular origins of glomerulosclerosis involve activation of parietal epithelial cells (PECs) and progressive podocyte depletion. While mammalian target of rapamycin-mediated (mTOR-mediated) podocyte hypertrophy is recognized as an important signaling pathway in the context of glomerular disease, the role of podocyte hypertrophy as a compensatory mechanism preventing PEC activation and glomerulosclerosis remains poorly understood. In this study, we show that glomerular mTOR and PEC activation-related genes were both upregulated and intercorrelated in biopsies from patients with focal segmental glomerulosclerosis (FSGS) and diabetic nephropathy, suggesting both compensatory and pathological roles. Advanced morphometric analyses in murine and human tissues identified podocyte hypertrophy as a compensatory mechanism aiming to regulate glomerular functional integrity in response to somatic growth, podocyte depletion, and even glomerulosclerosis - all of this in the absence of detectable podocyte regeneration. In mice, pharmacological inhibition of mTOR signaling during acute podocyte loss impaired hypertrophy of remaining podocytes, resulting in unexpected albuminuria, PEC activation, and glomerulosclerosis. Exacerbated and persistent podocyte hypertrophy enabled a vicious cycle of podocyte loss and PEC activation, suggesting a limit to its beneficial effects. In summary, our data highlight a critical protective role of mTOR-mediated podocyte hypertrophy following podocyte loss in order to preserve glomerular integrity, preventing PEC activation and glomerulosclerosis.

Dexmedetomidine enhances ropivacaine-induced sciatic nerve injury in diabetic rats

BACKGROUND

Previous studies suggest that dexmedetomidine has a protective effect against local anaesthetic-induced nerve injury in regional nerve blocks. Whether this potentially protective effect exists in the context of diabetes mellitus is unknown.

METHODS

A diabetic state was established in adult male Sprague-Dawley rats with intraperitoneal injection of streptozotocin. Injections of ropivacaine 0.5%, dexmedetomidine 20 μg kg^-1 (alone and in combination), or normal saline (all in 0.2 ml) were made around the sciatic nerve in control and diabetic rats (n=8 per group). The duration of sensory and motor nerve block and the motor nerve conduction velocity (MNCV) were determined. Sciatic nerves were harvested at post-injection day 7 and assessed with light and electron microscopy or used for pro-inflammatory cytokine measurements.

RESULTS

Ropivacaine and dexmedetomidine alone or in combination did not produce nerve fibre damage in control non-diabetic rats. In diabetic rats, ropivacaine induced significant nerve fibre damage, which was enhanced by dexmedetomidine. This manifested with slowed MNCV, decreased axon density, and decreased ratio of inner to outer diameter of the myelin sheath (G ratio). Demyelination, axon disappearance, and empty vacuoles were also found using electron microscopy. An associated increase in nerve interleukin-1β and tumour necrosis factor-α was also seen.

CONCLUSIONS

Ropivacaine 0.5% causes significant sciatic nerve injury in diabetic rats that is greatly potentiated by high-dose dexmedetomidine. Although the dose of dexmedetomidine used in this study is considerably higher than that used in clinical practice, our data suggest that further studies to assess ropivacaine (alone and in combination with dexmedetomidine) use for peripheral nerve blockade in diabetic patients are warranted.

Unified decomposition method to study Rayleigh-Taylor instability in liquids and solids

In the previous studies of Rayleigh-Taylor instability, different methods were used to consider the effects of elasticity, viscosity, and magnetic fields. In this paper, a unified method, which was first used for fluids, is validated for different physical models, where the unstable mode is decomposed into an irrotational part and a rotational part, and the latter one includes the effects of nonconservative forces and constitutive relations. Previous results of solid and liquid with or without the effects of magnetic fields and finite thickness can be easily recovered after applying the corresponding interface boundary conditions. In addition, new approximate but analytical solutions of the growth rates for a semi-infinite solid-solid interface and solid-fluid interface are obtained with substantially improved accuracy in comparison with the previous ones.

Atmospheric ammonia alters lipid metabolism-related genes in the livers of broilers (Gallus gallus)

Atmospheric ammonia in animal housing is reported to have adverse effects on livestock performance and animal health. Previous experiments have found that 75 ppm ammonia reduced the production performance and altered body fat distribution quality of broilers. In this study, we examined the body fat distribution, serum metabolites and lipid metabolism gene expression of broiler exposed to ammonia. A total of 400 chickens were randomly allocated to four groups with four replicates and received ammonia treatments at 0, 25, 50 and 75 ppm, respectively, for 3 weeks. The average daily feed intake and weight gain were decreased when broiler was exposed to ammonia concentration exceeding 50 ppm (p < .05). The increased abdominal fat and reduced thickness of subcutaneous adipose were found in broilers of 75 ppm group (p < .05). When ammonia exceeded 50 ppm, the content of fat in breast muscle of broiler was increased, and when ammonia was higher than 25 ppm, the fat in liver was increased (p < .05). It showed that the fat content in liver was a sensitive index for broilers exposed to ammonia. Furthermore, ammonia exposure had no significant effect on total cholesterol and triglyceride in serum, but significantly increased the relative mRNA expression of acetyl-CoA carboxylase (p = .046) and malic enzyme in liver (p = .038), which indicated that ammonia exposure may increase the de novo fat synthesis in liver. In addition, ammonia increased the high-density lipoprotein cholesterol (p = .02) and activity of hepatic lipase in serum (p < .001), which indicated that ammonia exposure may improve the transportation of cholesterol to liver. To conclude, our results indicated that ammonia exposure might increase the de novo fat synthesis in liver and increased the transportation of cholesterol to liver. In addition, the concentration of ammonia in poultry house should be limited lower than 25 ppm based on the variation of hepatic fat content.

Targeted ultrasound molecular imaging in mouse atherosclerotic plaque model

This study aims to assess the early diagnosis of mouse atherosclerotic plaque through targeted ultrasound molecular imaging. Forty Apolipoprotein E-deficient (ApoE-/-) mice and 40 C57BL/6 wild type mice were randomly divided into 4 groups, 20 mice per group. Mice included in the study group were fed with high cholesterol diet for 20 weeks, after which the targeted ultrasound microbubbles were prepared. The mice with atherosclerotic plaque were studied with targeted ultrasound molecular imaging in comparison with red oil O staining. The results of targeted ultrasound molecular imaging of atherosclerotic plaque indicate that the GP Ib and GP IIb/IIIa are viable biomarkers for early diagnosis of vulnerable atherosclerotic plaque. The targeted ultrasound molecular imaging is worth studying in order to identify the atherosclerotic progress as a noninvasive effective identification method which could be used widely.

Nickel oxide nanoparticles induced pulmonary fibrosis via TGF-β1 activation in rats

Nano nickel oxide (NiO), widely used in industry, has recently been discovered to have pulmonary toxicity. However, no subchronic exposure studies about nano NiO-induced pulmonary fibrosis have been reported. The objective of this study was to investigate pulmonary fibrosis induced by nano NiO and its potential mechanism in rats. Male Wistar rats ( n = 40, 200–240 g) were randomized into control group, nano NiO groups (0.015, 0.06, and 0.24 mg/kg), and micro NiO group (0.024 mg/kg). All rats were killed to collect lung tissue after intratracheal instillation of NiO particles twice a week for 6 weeks. To identify pulmonary fibrosis, Masson trichrome staining, hydroxyproline content, and collagen protein expression were performed. The results showed widespread lung fibrotic injury in histological examination and increased content of hydroxyproline, collagen types I and III in rat lung tissue exposed to nano NiO. To explore the potential pulmonary fibrosis mechanism, transforming growth factor beta 1 (TGF- β1) content was measured by enzyme-linked immunosorbent assay, and the messenger RNA expression of key indicators was detected by reverse transcription-quantitative polymerase chain reaction (RT-qPCR). The TGF- β1 content was increased in nano NiO exposure groups, as well as the upregulated gene expression of TGF- β1, Smad2, Smad4, matrix metalloproteinase, and tissue inhibitor of metalloproteinase. The findings indicated that nano NiO could induce pulmonary fibrosis, which may be related to TGF- β1 activation.

Hydrodynamic instability of elastic-plastic solid plates at the early stage of acceleration

A model is presented for the linear Rayleigh-Taylor instability taking place at the early stage of acceleration of an elastic-plastic solid, when the shock wave is still running into the solid and is driven by a time varying pressure on the interface. When the the shock is formed sufficiently close to the interface, this stage is considered to follow a previous initial phase controlled by the Ritchmyer-Meshkov instability that settles new initial conditions. The model reproduces the behavior of the instability observed in former numerical simulation results and provides a relatively simpler physical picture than the currently existing one for this stage of the instability evolution.

Polluted dust derived from long-range transport as a major end member of urban aerosols and its implication of non-point pollution in northern China

The contribution of polluted dust transported from local and distal sources remains poorly constrained due to their similar geophysical and geochemical properties. We sampled aerosols in three cities in northern China (Xi'an, Beijing, Xifeng) during the spring of 2009 to determine dust flux, magnetic susceptibility and elemental concentrations. Combining dust fluxes with wind speed and regional visibility records enabled to differentiate between dust transported from long range and derived from local sources, while the combination of magnetic susceptibility and enrichment factors (EF) of heavy metals (Pb, Zn) allowed to distinguish natural aerosols from polluted ones. Our results indicate that polluted dust from long-range transport became a major end member of urban dust aerosols. Human settlements as its potential sources were confirmed by a pollutant enriched regional dust event originating from populated areas to the south as inferred by back trajectory modeling, implying their non-point source nature of dust pollution.

Losartan attenuates paraquat-induced pulmonary fibrosis in rats

Paraquat (PQ) is one of the most widely used herbicides in the world and can cause pulmonary fibrosis in the cases with intoxication. Losartan, an angiotensin II type 1 receptor antagonist, has beneficial effects on the treatment of fibrosis. The aim of this study was to examine the effect of losartan on pulmonary fibrosis in PQ-intoxicated rats. Adult male Sprague Dawley rats (n = 32, 180-220 g) were randomly assigned to four groups: (i) control group; (ii) PQ group; (iii) PQ + losartan 7d group; and (iv) PQ + losartan 14d group. Losartan treatment (intragastrically (i.g.), 10 mg/kg) was performed for 7 and 14 days after a single i.g. dose of 40 mg/kg PQ. All rats were killed on the 16th day, and hematoxylin-eosin and Masson's trichrome staining were used to examine lung injury and fibrosis. The levels of hydroxyproline and transforming growth factor β1 (TGF-β1), matrix metallopeptidase 9 (Mmp9), and tissue inhibitor of metalloproteinase 1 (TIMP-1) messenger RNA (mRNA) expression and relative expression levels of collagen type I and III were also detected. PQ caused a significant increase in hydroxyproline content, mRNA expression of TGF-β1, Mmp9, and TIMP-1, and relative expression levels of collagen type I and III ( p < 0.05), while losartan significantly decreased the amount of hydroxyproline and downregulated TGF-β1, Mmp9, and TIMP-1 mRNA and collagen type I and III expressions ( p < 0.05). Histological examination of PQ-treated rats showed lung injury and widespread inflammatory cell infiltration in the alveolar space and pulmonary fibrosis, while losartan could markedly reduce such damage and prevent pulmonary fibrosis. The results of this study indicated that losartan could reduce lung damage and prevent pulmonary fibrosis induced by PQ.

Molecular characterization and functional analysis of a Flowering locus T homolog gene from a Phalaenopsis orchid

Warm day and cool night conditions significantly induce reproductive spike formation in Phalaenopsis plants; hence, determining the flowering mechanism regulating the reproductive transition is important. Flowering locus T (FT) plays important roles in flowering induction in several plants. To explore spike induction by warm days and cool nights in Phalaenopsis orchids, we isolated the FT (PhFT) from Phalaenopsis hybrid Fortune Saltzman. The cDNA of PhFT was 809-bp long and contained a 531-bp open reading frame encoding a putative protein of 176 amino acids, a 58-bp 5'-untranslated region (UTR), and a 220-bp 3'-UTR. The predicted molecular mass of PhFT was 19.80 kDa, with an isoelectric point of 8.68. The PhFT was predicted to possess the conserved functional regions of the phosphatidylethanolamine-binding protein superfamily. Nucleotide sequence data indicated that PhFT contained 3 introns and 4 exons. Sequence alignment and phylogenetic analyses of PhFT revealed high homology to the FT proteins of Cymbidium goeringii and Oncidium Gower Ramsey. Quantitative real-time polymerase chain reaction analysis indicated that PhFT mRNA was expressed in roots, apical leaves, mature leaves, and flowers. In flowers, PhFT was expressed more in developing floral buds than in mature flowers and was predominantly expressed in ovaries and petals. Ectopic expression of PhFT in Arabidopsis ft-1 mutants showed novel early-flowering phenotypes that lost their siliques. Our results indicated that the ectopic expression of PhFT could partially complement the late flowering defect in transgenic Arabidopsis ft-1 mutants. Our findings suggest that PhFT is a putative FT homolog in Phalaenopsis plants that regulates flowering transition.

Rayleigh-Taylor linear growth at an interface between an elastoplastic solid and a viscous liquid

A previously developed model for the Rayleigh-Taylor instability at an interface between an elastoplastic solid and a viscous fluid [Piriz, Sun, and Tahir, Phys. Rev. E 88, 023026 (2013)] has been used for calculating the time evolution of the perturbations in terms of the mechanical properties of the solid and the liquid, as well as of the initial amplitude ξ_{0} and the wavelength λ of the perturbation. Four kinds of possible evolution are found: two stable and two unstable, depending on their positions in the space of parameters (ξ_{0},λ). All of them present some features that are independent of the solid properties and that are determined only by the liquid viscosity.

Identification of warm day and cool night conditions induced flowering-related genes in a Phalaenopsis orchid hybrid by suppression subtractive hybridization

The influence of warm day and cool night conditions on induction of spikes in Phalaenopsis orchids has been studied with respect to photosynthetic efficiency, metabolic cycles and physiology. However, molecular events involved in spike emergence induced by warm day and cool night conditions are not clearly understood. We examined gene expression induced by warm day and cool night conditions in the Phalaenopsis hybrid Fortune Saltzman through suppression subtractive hybridization, which allowed identification of flowering-related genes in warm day and cool night conditions in spikes and leaves at vegetative phase grown under warm daily temperatures. In total, 450 presumably regulated expressed sequence tags (ESTs) were identified and classified into functional categories, including metabolism, development, transcription factor, signal transduction, transportation, cell defense, and stress. Furthermore, database comparisons revealed a notable number of Phalaenopsis hybrid Fortune Saltzman ESTs that matched genes with unknown function. The expression profiles of 24 genes (from different functional categories) have been confirmed by quantitative real-time PCR in induced spikes and juvenile apical leaves. The results of the real-time PCR showed that, compared to the vegetative apical leaves, the transcripts of genes encoding flowering locus T, AP1, AP2, KNOX1, knotted1-like homeobox protein, R2R3-like MYB, adenosine kinase 2, S-adenosylmethionine synthetase, dihydroflavonol 4-reductase, and naringenin 3-dioxygenase accumulated significantly higher levels, and genes encoding FCA, retrotransposon protein Ty3 and C3HC4-type RING finger protein accumulated remarkably lower levels in spikes of early developmental stages. These results suggested that the genes of two expression changing trends may play positive and negative roles in the early floral transition of Phalaenopsis orchids. In conclusion, spikes induced by warm day and cool night conditions were complex in Phalaenopsis orchids; nevertheless, several molecular flowering pathway-related genes were found. The acquired data form the basis for a molecular understanding of spike induction by warm day and cool night conditions in Phalaenopsis orchids.

Rayleigh-Taylor stability boundary at solid-liquid interfaces

A previous model for the Rayleigh-Taylor instability [A. R. Piriz, J. J. López Cela, and N. A. Tahir, Phys. Rev. E 80, 046305 (2009)] has been extended in order to study an interface between an elastic-plastic solid and a Newtonian liquid and determine the stability region given by the initial perturbation amplitude ξ(0) and wavelength λ. The stability region is found to be enhanced by the effect of the liquid viscosity, but it reaches an asymptote for a sufficiently high viscosity. In addition, it is also found that the boundary for the transition from the elastic to the plastic regime get closer to the stability boundary up to both boundaries coincide for a high enough liquid viscosity, thus making the onset of plastic flow a sufficient condition for instability.

2,3-Butanedione monoxime increases speed of relaxation in single muscle fibres of frog

The effects of 2,3-butanedione monoxime (BDM) on intracellular Ca2+ transient and cross-bridge function were studied in frog single fibres from the anterior tibialis muscle of Rana temporaria (sarcomere length, 2.2 microm; temperature, 2-4 degrees C). The fluorescent dye fluo-3 was used to monitor the intracellular free calcium concentration ([Ca2+]i) during isometric contractions. BDM (1-5 mM) reduced the amplitude of the Ca2+ transient during twitches, but this effect was too small to explain the marked inhibition of BDM on twitch force. [Ca2+]i reached at the end of 1-s tetanic stimulation was not significantly affected by BDM (1.0 and 1.8 mM) while the maximum tetanic tension was substantially reduced. The rate of relaxation during isometric tetanus was increased by BDM whereas the rate of decay of the Ca2+ transient was reduced in the presence of BDM. The results strongly suggest that BDM, under the experimental conditions used, mainly affects the contractile machinery resulting in altered performance of the cross-bridges. These effects of BDM were evaluated in terms of the cross-bridge model of Huxley (1957) which was fitted to the experimental force-velocity data in the presence and absence of BDM.

Effects of sarcomere length and temperature on the rate of ATP utilisation by rabbit psoas muscle fibres

1. The steady state rate of ATP utilisation by single permeabilised fibres from rabbit psoas muscle immersed in silicone oil was measured using a linked enzyme assay that coupled ADP production to the oxidation of NADH.2. At sarcomere length 2.5 microm, at 10 degrees C, the rate of ATP utilisation in relaxing conditions was 6 +/- 1 microM s-1 (mean +/- S.E.M., n = 8 fibres); during isometric contraction it was 310 +/- 10 microM s-1 (mean +/- S.E.M., n = 11). Assuming a myosin active site concentration of 150 microM, these values correspond to rates of ATP utilisation per active site of about 0.04 and 2.1 s-1, respectively. 3. The rate of ATP utilisation in relaxing conditions was independent of sarcomere length in the range 2.5-4.0 microm. The rate of ATP utilisation during isometric contraction had a dependence on resting sarcomere length similar to that of isometric force in the range 2.5-4.0 microm, but was less strongly dependent on sarcomere length than was isometric force in the range 1.5-2.5 microm. 4. The rate of ATP utilisation in relaxing conditions had a Q10 of 2.5 in the temperature range 7-25 degrees C, but this increased to 9.7 in the range 25-35 degrees C, suggesting that some active force may have been generated in relaxing solution at temperatures above 25 degrees C. 5. The rate of ATP utilisation during isometric contraction had a Q10 of 3.6 throughout the temperature range 7-25 degrees C; this was similar to the Q10 for isometric force at low temperature (3.5 at 7-10 degrees C) but much larger than that for isometric force at higher temperature (1.3 at 20-25 degrees C). 6. Application of the NADH-linked assay to single muscle fibres in oil improves the effective sensitivity and time resolution of the method, and allows continuous measurements of the rate of ADP production during active contraction.

Effect of active shortening on the rate of ATP utilisation by rabbit psoas muscle fibres

1. The rate of ATP utilisation during active shortening of single skinned fibres from rabbit psoas muscle at 10 degrees C was measured using an NADH-linked assay. Fibres were immersed in silicone oil and illuminated with 365 nm light. The amounts of NADH and carboxytetramethylrhodamine (CTMR) in the illuminated region of the fibre were measured simultaneously from fluorescence emission at 425-475 and 570-650 nm, respectively. The ratio of these two signals was used to determine the intracellular concentration of NADH, and thus the ATP utilisation, without interference from movements of the fibre with respect to the measuring light beam. 2. The total extra ATP utilisation due to shortening (ATP) was determined by extrapolation of the steady isometric rates before and after shortening to the mid-point of the shortening period. ATP had a roughly linear dependence on the extent of shortening in the range 1-15 % fibre length (L0) at a shortening velocity of 0.4 L0 s-1 from initial sarcomere length 2.7 microm. For shortening of 1 % L0, ATP was 21 +/- 1 M (mean +/- S.E.M., n = 3). 3. The mean rate of ATP utilisation during ramp shortening of 10 % L0 had a roughly linear dependence on shortening velocity in the range 0.05-1.2 L0 s-1. During unloaded shortening at 1.2 L0 s-1 the mean rate of ATP utilisation was 1.7 mM s-1, about 9 times the isometric rate. ATP was roughly independent of shortening velocity, and was 84 +/- 9 microM (mean +/- S.E.M., n = 6) for shortening of 10 % L0. 4. The implications of these results for mechanical-chemical coupling in muscle are discussed. The total ATP utilisation associated with shortening of 1 % L0 is only about 17 % of the concentration of the myosin heads in the fibre, suggesting that during isometric contraction either less than 17 % of the myosin heads are attached to actin, or that heads can detach without commitment to ATP splitting. The fraction of myosin heads attached to actin during unloaded shortening is estimated from the rate of ATP utilisation to be less than 7 %.

Conformation of the myosin motor during force generation in skeletal muscle

Myosin motors drive muscle contraction, cytokinesis and cell locomotion, and members of the myosin superfamily have been implicated in an increasingly diverse range of cell functions. Myosin can displace a bound actin filament several nanometers in a single interaction. Crystallographic studies suggest that this 'working stroke' involves bending of the myosin head between its light chain and catalytic domains. Here we used X-ray fiber diffraction to test the crystallographic model and measure the interdomain bending during force generation in an intact single muscle fiber. The observed bending has two components: an elastic distortion and an active rotation that generates force. The average bend of the force-generating myosin heads in a muscle fiber is intermediate between those in crystal structures with different bound nucleotides, and the C-terminus of the head is displaced by 7 nm along the actin filament axis compared with the in vitro conformation seen in the absence of nucleotide.

Relaxant effects of pyranocoumarin compounds isolated from a Chinese medical plant, Bai-Hua Qian-Hu, on isolated rabbit tracheas and pulmonary arteries

Qian-Hu is a well-known traditional Chinese medicine used for the treatment of respiratory diseases and pulmonary hypertension. We compared the relaxant effects of pyranocoumarin compounds, including (+)-praeruptorin A (Pra-C), Pd-Ia (=(+/-)-praeruptorin A), pteryxin, peucedanocoumarin II (P-II) and 8-methoxy-psoralen (8-MOP) purified from Bai-Hua Qian-Hu (BQ) in isolated rabbit tracheas and pulmonary arteries. Pra-C, pteryxin and Pd-Ia produced significant relaxant effects in tracheal preparations constricted with 40 mM KCl or 10 microM acetylcholine. The relaxant response to Pra-C, pteryxin or Pd-Ia in preparations constricted with KCl was significantly more potent than that in preparations constricted with acetylcholine. Pra-C, pteryxin or Pd-Ia at a concentration of 30 microM completely relaxed tracheas constricted with 40 mM KCl, whereas P-II at the same concentration showed only partial relaxation. In pulmonary arterial preparations, 8-MOP produced a significant relaxant effect on contractions by 10 microM phenylephrine, without any effect on the contraction by 40 mM KCl. These results suggest that Pd-Ia, pteryxin and Pra-C for their calcium antagonistic action, and 8-MOP for its inhibitory effect on contraction induced by phenylephrine, may be the active principles of BQ for relaxing the smooth muscle of tracheas and pulmonary arteries, and the principle may produce a synergistic effect.

The relationship between the intracellular Ca2+ transient and the isometric twitch force in frog muscle fibres

The calcium-sensitive fluorescent indicator fluo-3 was used to monitor the intracellular free calcium concentration ([Ca2+]i) during isometric twitches in twenty-nine single muscle fibres from the anterior tibialis muscle of Rana temporaria (sarcomere length, 2.2 microns; 2-4 degrees C). The transient change in [Ca2+]i in response to a single stimulus was very brief. The time to peak and the duration of the Ca2+ signal, measured at 50% of the peak amplitude, were 8.3 +/- 0.2 and 22.1 +/- 1.4 ms (mean +/- S.E.M., n = 29), respectively. The mean peak amplitude of the Ca2+ transient was 3.2 +/- 0.1 microM, ranging from 2.46 to 3.92 microM among the different fibres. The isometric force started to rise 2.5 ms before [Ca2+]i reached its maximum value. When peak twitch force was attained, [Ca2+]i had already declined to approximately 10% of its maximum value. The peak force produced during a twitch was closely related to the decay phase of the Ca2+ transient, a slower decay of [Ca2+]i being associated with a greater amplitude of the twitch. The amplitude and duration of the Ca2+ transient varied in a systematic way relative to one another in different fibres, in that a greater amplitude was associated with a more rapid decay of the Ca2+ transient. NO3- and Zn2+ added to the external medium greatly enhanced the peak twitch force without markedly affecting the amplitude of the Ca2+ transient. However, both agents delayed the decay of [Ca2+]i. It is concluded that the decay phase of the Ca2+ transient is a more important determinant of the mechanical response during an isometric twitch than is the peak amplitude of the transient.

The effects of 2,3-butanedione monoxime (BDM) on the force-velocity relation in single muscle fibres of the frog

The effects of 2,3-butanedione monoxime (BDM) on the force-velocity relation were studied in single fibres from the anterior tibialis muscle of Rana temporaria (2.2 microns sarcomere length, temperature 1.9-2.4 degrees C). BDM (1.0 and 1.8 mM) suppressed the maximum tetanic force (P0) and the maximum speed of shortening (Vmax), and increased the main curvature of the force-velocity relation. The biphasic shape of the force-velocity curve was maintained well in the presence of BDM, but the interrelation between the two portions of the force-velocity relation was significantly changed. Caffeine (0.5 mM) added in the presence of BDM increased the initial rate of rise of force during twitch and tetanus, increased the twitch amplitude, but did not affect the maximum tetanic force. The latter finding suggests that the contractile system was fully activated during tetanus in the presence of BDM. The results support the view that BDM affects the cross-bridge function by exerting a direct action upon the contractile apparatus. The decrease in tetanic force and the change of the force-velocity relation induced by BDM may be interpreted to show that a larger fraction of the attached cross-bridges is in a state of low force production under the influence of BDM. This view is further supported by the observation that the instantaneous stiffness of the muscle fibre is reduced proportionally less by BDM than the tetanic force.

Moderate fatigue studied at great sarcomere lengths in frog single muscle fibres

Single fibres from the anterior tibialis muscle of Rana temporaria (temperature, 2-3 degrees C) were moderately fatigued at a prestretched sarcomere length (approximately 3.6 microns) by reducing the intervals between 2 s tetani from 240 to 20 s. Changes in length of marked segments along the muscle fibre were monitored during fixed-end tetani using a photoelectric recording system. In contrast to the situation at 2.2 microns sarcomere length, the central region of the fibre was elongated during tetanus at the prestretched fibre length, whereas the segments next to the fibre-tendon junctions (end segments) shortened correspondingly. These length changes were associated with a slow climb of force (tension creep). During development of fatigue, the maximum tetanic tension was reduced to about 78% of the control value and the time course of the tetanus was markedly changed. The tension creep observed in control tetanus was greatly reduced during fatigue, the tetanic tension remaining nearly constant after an initial rising phase. The change in shape of the force myogram during fatigue was associated with a considerable reduction in the amplitude of segment movements along the fibre. The results are explainable by assuming that the end segments (having shorter sarcomeres) become more fatigued than other parts in series along the fibre. At the same time the central segments are likely to have acquired a higher ability to resist stretch by the end segments.

Variation in myoplasmic Ca2+ concentration during contraction and relaxation studied by the indicator fluo-3 in frog muscle fibres

1. The fluorescent dye fluo-3, in its permeant acetoxymethyl form, was used to monitor calcium transients during twitch and tetanus of single fibres isolated from the anterior tibialis muscle of Rana temporaria (2-5 degrees C). 2. Fluo-3 was loaded into the muscle fibre by diffusion. Under the experimental conditions used, approximately 45% of maximal fluorescence was reached during a 1 s fused isometric tetanus. Fluo-3 had no detectable effect on the mechanical response of the fibre. 3. The free calcium concentration in the myoplasm, [Ca2+]i, and its variation with time, was calculated from the fluorescence signal by accounting for the on- and off-rate constants for the binding of calcium to the dye. The time course of the calcium transient during twitch and tetanus determined in this way agreed well with previous measurements based on fast-reacting calcium-sensitive dyes. 4. [Ca2+]i declined steeply during the initial phase of force relaxation in both twitch and tetanus, but exhibited a secondary rise that closely coincided with the pseudoexponential fall of tension after the shoulder in the tetanus myogram. The rate of decay of [Ca2+]i during relaxation and the rate of decline of force both became progressively reduced by repetitive stimulation. 5. Stretch and shortening ramps performed during the plateau of an isometric tetanus had no detectable effect upon the calcium transient during the movement. By contrast, shortening and stretch imposed during the linear phase of relaxation both led to an increase of [Ca2+]i and to a steepening of the relaxation phase. 6. The results strongly suggest that the non-uniform length changes that are known to occur along a muscle fibre during relaxation enhance the release of calcium from the contractile system. The calcium mobilized in this way probably accounts for the transitory increase of [Ca2+]i that is observed during the latter part of force relaxation.

The high-force region of the force-velocity relation in frog skinned muscle fibres

The force-velocity relation has been studied during calcium-induced contracture of chemically skinned fibres from the semitendinosus muscle of Rana temporaria with special interest focused on the high-load region. The force-velocity curve was hyperbolic at low and intermediate loads but departed below the hyperbola as the load exceeded about 80% of the isometric force (P0). The force intercept (P*0) of the hyperbola derived from force-velocity data truncated at 0.78 P0 was higher than P0 (P*0/P0 = 1.14 +/- 0.04). At submaximum Ca2+ concentration, where the isometric force of the fibre was 65-75% of the maximum value, the force-velocity data still departed below the hyperbola at high loads (P*0/P0 = 1.09 +/- 0.04). The departure of the force-velocity data from the hyperbola at high force was also found at high ionic strength (250 mM), but not at low ionic strength (150 mM) (P*0/P0 = 1.09 +/- 0.03 and 0.98 +/- 0.03, respectively). The force-velocity relations derived under different experimental conditions could be fitted well by a modified version of Hill's (1938) hyperbolic equation (Edman 1988) using similar numerical values of k1 and k2 in the latter equation. The results indicate that the force-velocity relation in skinned muscle fibres is biphasic, and that the two curvatures, as in intact muscle fibres, are closely related to one another. Furthermore the evidence supports the hypothesis that the altered shape of the force-velocity relation at high loads is not related to the force level per se but rather to the speed of shortening of the contractile system (Edman 1992).

Vasectomy and spermatic granuloma in hamsters

Fifty-eight hamsters were bilaterally vasectomized either 1, 2, 3 or 6 months before experimentation. Fifty-five sham-vasectomized hamsters served as control. Cauda epididymal fluid was obtained by micropuncture. The effect of vasectomy on the incidence of spermatic granuloma was studied. The data were analyzed according to the presence or absence of granuloma after vasectomy and were compared with the data of their respective control. The incidence of granuloma increased with the duration of vasectomy and reached 92.8% at the end of 6 months after operation. Distension of the epididymis increased to a maximum at 1 month, but recovered to nearly normal irrespective of the existence of granuloma. The weight of the testis, spermatocrit and sperm density significantly decreased, and the percentage of abnormal sperm in the cauda and caput increased markedly in the absence of granuloma compared with their respective tract with granuloma or control. The testes in both the group with and without granuloma showed marked atrophy 6 months after vasectomy. The concentration of carnitine in the cauda epididymal plasma was significantly reduced from 2-6 months. The possible protective effect of a granuloma formation is discussed.

Effect of (D-Trp6, Pro9-NEt)-GnRH on the function and ultrastructure of pituitary and testis in male rats

Groups of ten adult male Wistar rats were treated chronically with GnRH agonist for different durations. The responses of pituitary and testis to GnRH agonist were evaluated by serum and testicular testosterone, serum and pituitary LH, and testicular LH receptors. Testicular testosterone and LH receptors were decreased very significantly under our experimental regimen, irrespective of the duration of the treatment Serum testosterone levels were reduced after 10 and 15 injections, but only rats receiving 10 injections showed a significant increase in serum LH levels and decrease of pituitary LH content. The type II gonadotropes of the pars distalis of pituitary were increased in number but showed a higher degree of dilated smooth endoplasmic reticulum with few secretory granules. Many large lipid droplets appeared in the cytoplasms of the Leydig cells. Degenerative changes were observed in most seminiferous tubules following GnRH agonist treatment. Obvious abnormal acrosome and nuclear caps of some spermatids were also observed. The functional changes caused by GnRH agonist coincided with their ultrastructural appearance.

Antifertility effect of polyvinylpyrrolidone-gossypol and gossypol in male rats

Thirty-nine adult male Wistar rats were administered 20 mg/kg or 24.3 mg/kg polyvinylpyrrolidone-gossypol (PVP-G) and 20 mg/kg gossypol acetic acid (G-A) 6 times a week for 6 weeks. Mating test was taken to evaluate the antifertility effect. Caudal sperm count, body weight, sex and accessory sex organ weights were recorded. At the end of 6 weeks treatment, the recovery period of 6 weeks was investigated. The results showed that the onset of antifertility action and recovery with PVP-G are faster than with G-A.