Frequency response of Pinus Pinea L. for selective cone harvesting by vibration

The stone pine (Pinus pinea L.) is exploited for wood production and its edible kernels. Cones take 3 years to mature, while other newer cones are growing on the tree. Currently, mechanical cone harvesting by tree vibration drives the profitability and development of this crop in forest ecosystems. However, the adaptation of vibration parameters is necessary to avoid damage to the tree and for the implementation of good harvesting practices. Direct measurements of acceleration transmissibility along fruit-bearing branches under controlled laboratory conditions showed that vibrations in the frequency range of 18.0 ± 5.3 Hz were capable of producing resonance phenomena in mature cones. Morphological changes produced in the mature cones, especially in the stalk and total weight, amplified the acceleration transmissibility, providing more favourable conditions for fruit detachment. Field tests with stone pines and a trunk shaker confirmed the potential of selective mechanical harvesting, which is conditional on the vibration parameters applied. The frequency range of the resonance of the mature cone proved to be suitable for vibration of the tree at its trunk. The quality and efficiency of the mechanical harvesting were determined to be inversely related parameters during harvesting by vibration. Trunk vibration at a frequency of 18 Hz and approximate acceleration of 65 m/s² achieved a high harvest quality, with limited detachment of shoots and unripe cones, and a harvesting efficiency near 85%.     

Physical and physiological aspects of gear efficiency in North Sea brown shrimp fisheries

In search of means to reduce the by-catch of juvenile flatfish in the shrimp fishery, vibrations and changes in current velocity caused by shrimp trawls were investigated in the field and in the laboratory. Buried as well as emerged shrimps (Crangon crangon) exhibit tailflips 5–10 cm before being touched by the rollers of a shrimp gear approaching them at a speed of 0.5 m·sec⁻¹, as was revealed by slow motion video recordings in aquaria under artificial light. Hence, the signal effective in triggering escape must be attenuated strongly with increasing distance. Sediment vibration, commonly assumed to be an important signal in triggering escape of shrimps, was found to decrease by a factor 100·m⁻¹. Signals from the rollers of a commercial shrimp gear in operation (towing speed 1 m·sec⁻¹) were directly recorded with an accelerometer. Their frequency ranged from 50 to 500 Hz and reached an acceleration of 40 m·sec⁻² on soft bottom or up to 100 m·sec⁻² on hard substrate. Accelerometers, which had been buried right at the surface of a tidal sand flat during low tide, produced only one sharp signal of 100 Hz with an acceleration of 24 m·sec⁻², when a shrimp gear swept them on the submerged tidal flats. However, in aquaria short sinusoidal signals (<5 m·sec⁻²; 20 to 300 Hz) made buried shrimps and flatfish (Pleuronectes platessa, Solea solea, Microstomus kitt) hide rather than flee. The vibrations recorded directly at the rollers and the underlying jolting movements of the rollers induce corresponding pulses in the water surrounding the rollers in a layer of approximately 10–15 cm. Similar water displacement of high acceleration was experimentally produced by a spring loaded transparent lucite piston (7 cm in diameter) fitted to an accelerometer. Accelerating this piston (12–116 m·sec⁻², 50–200 Hz range) from 5 cm above towards the shrimp produced escape responses in up to 94% of the tests. Arthropods are known to perceive medium displacement rather than pressure. Hence, strong and rapidly rising water currents caused by the rollers rather than sediment vibration are assumed to mainly trigger the escape reaction, which makesCrangon accessible to the gear.     

Neurophysiology of the vibration sense in locusts and bushcrickets: Response characteristics of single receptor units

The response characteristics of the vibration receptors in the legs of the migratory locust, Locusta migratoria, and the tettigoniid Decticus verrucivorus were investigated electro-physiologically by single cell recordings. The legs were stimulated by sinusoidal vibrations. There are four types of vibration receptor in each leg of Locusta and Decticus, which can be classified physiologically. One type—most probably campaniform sensilla—shows a phase-locked response to vibrations from 30 to 200 Hz, its threshold reflecting the displacement. A second type shows similar responses in the same frequency range, but its reactions depend on the stimulus acceleration. The receptor cells of the subgenual organ are very sensitive to vibration from 30 to at least 5000 Hz, and their responses depend on acceleration. There are two types of subgenual receptors, one of which shows a clear maximum of sensitivity between 200 and 1000 Hz, with a threshold below 0.01 m/sec^?2 acceleration. Subgenual receptors with different thresholds and different characteristic frequencies occur in each leg. The receptors of each leg pair have quite similar mean sensitivities and characteristic frequencies. However, in the front legs of tettigoniids the more sensitive subgenual receptors and an additional receptor type also respond to low-frequency airborne sound up to 10 kHz.     

Vibration of osteoblastic cells using a novel motion-control platform does not acutely alter cytosolic calcium,but desensitizes subsequent responses to extracellular ATP

Low-magnitude high-frequency mechanical vibration induces biological responses in many tissues. Like many cell types, osteoblasts respond rapidly to certain forms of mechanostimulation, such as fluid shear, with transient elevation in the concentration of cytosolic free calcium ([Ca²⁺]_i). However, it is not known whether vibration of osteoblastic cells also induces acute elevation in [Ca²⁺]_i. To address this question, we built a platform for vibrating live cells that is compatible with microscopy and microspectrofluorometry, enabling us to observe immediate responses of cells to low-magnitude high-frequency vibrations. The horizontal vibration system was mounted on an inverted microscope, and its mechanical performance was evaluated using optical tracking and accelerometry. The platform was driven by a sinusoidal signal at 20–500 Hz, producing peak accelerations from 0.1 to 1 g. Accelerometer-derived displacements matched those observed optically within 10%. We then used this system to investigate the effect of acceleration on [Ca²⁺]_i in rodent osteoblastic cells. Cells were loaded with fura-2, and [Ca²⁺]_i was monitored using microspectrofluorometry and fluorescence ratio imaging. No acute changes in [Ca²⁺]_i or cell morphology were detected in response to vibration over the range of frequencies and accelerations studied. However, vibration did attenuate Ca²⁺ transients generated subsequently by extracellular ATP, which activates P2 purinoceptors and has been implicated in mechanical signaling in bone. In summary, we developed and validated a motion-control system capable of precisely delivering vibrations to live cells during real-time microscopy. Vibration did not elicit acute elevation of [Ca²⁺]_i, but did desensitize responses to later stimulation with ATP.     

Ein auf Substratvibration reagierendes Interneuron im Bauchmark der Grille

Summary By extracellular recording from the neck connectives of free moving crickets potentials of large fibres can be obtained, which respond to substratum vibration. The most sensitive fibres which seem to be connected to the subgenual organs show an adaptation which can be modified by central or peripheral factors. The sensitivity of one fibre which was tested with a vibration platform of adjustable frequency and amplitude has a threshold of 0.2 to 0.3 cm/sec² of acceleration at a frequency of 500 Hz (Fig. 4). These data correspond with the results of threshold measurements on the subgenual organs made by Autrum and Schneider (1948).

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Die Untersuchungen wurden unterstützt durch Mittel der Deutschen Forschungsgemeinschaft, die Herrn Prof. Dr. F. Huber zur Verfügung standen.     

Transient electric birefringence of the bacteriophages T3 and T7

Electric birefringence measurements of suspensions of T3 and T7 bacteriophages in 10^?2 M phosphate buffer, pH 6.9, show that there is a difference in their rotational diffusion coefficient. The values corrected to 25°C and water viscosity are D_25,w = 4630 ± 130 sec^?1 and D_25,w = 5290 ± 260 sec^?1 for T3 and T7, respectively. The value obtained from shell model calculations (according to Filson and Bloomfield) is D_25,w = 4500 ± 600 sec^?1. The apparent permanent dipole moments are 4.5 × 10^?26 C·m and 1.7 × 10^?26 C·m for T3 and T7, respectively. For both phage particles the intrinsic optical anisotropy is +7.2 × 10^?3. It is shown that this anisotropy is mainly due to the DNA molecule inside the head of the phage. Its positive value means that there exists an excess orientation of the DNA helix perpendicular to the symmetry axis of the particle. For T7 an unexpectedly large increase of Δn_s and K_sp occurs at a glycerol concentration of about 30% (v/v). This increase is interpreted as being caused by a change of the shape of the particle and/or a change in the secondary structure of the DNA inside the head of the bacteriophage.     

低强度振动载荷刺激对于三维多孔钛合金内成骨细胞粘附和增殖的影响

目的:探究低强度振动载荷刺激对于三维多孔钛合金(porous titanium,pTi)内兔成骨细胞(osteoblasts,OB)粘附和增殖的影响,以期为临床振动载荷协同pTi治疗骨缺损提供重要的实验依据。方法:原代分离培养1日龄新生新西兰兔颅盖骨OB,待传至第3~6代以5×104/mL密度植入pTi中,随机分为振动组和对照组。振动组在5%CO2、37℃温度环境下进行3天低强度振动载荷(0.5 g,30 Hz)刺激,每天1 h;对照组放置在无载荷的振动平台上,分别采用DAPI核染色法和MTT法评价OB在p Ti中的粘附和增殖情况。结果:在振动载荷刺激下,每个视野下OB细胞在pTi上的粘附数量14±3个,对照组粘附数量6±2个,粘附能力显著增强(P0.05);在振动载荷刺激下,pTi上的OB细胞增殖吸光度为36.5%±0.8%,对照组吸光度为34%±1%,细胞增殖能力得到了显著促进(P0.05)。结论:低强度振动载荷刺激对于提高pTi中的OB细胞生物学活性具有促进作用,本研究为下一步系统探索振动载荷协同pTi对于骨缺损的修复效果奠定了基础。     

A Comparative Study of the Non-acidic Chemically Mediated Antifoulant Properties of Three Sympatric Species of Ascidians Associated with Seagrass Habitats

In this study, the mechanical properties of biofilms formed at the surface of nano-filtration (NF) membranes from a drinking water plant were analysed. Confocal laser scanning microscopy observations revealed that the NF biofilms formed a dense and heterogeneous structure at the membrane surface, with a mean thickness of 32.5 ± 17.7 μm. The biofilms were scraped from the membrane surface and analysed in rotation and oscillation experiments with a RheoStress 150 rotating disk rheometer. During rotation analyses, a viscosity decrease with speed of shearing characteristic of rheofluidification was observed (η = 300 Pa s for ý = 0.3 s^?1). In the oscillation analyses with a sweeping of frequency (1–100 Hz), elasticity (G′) ranged from 3000 to 3500 Pa and viscosity (G″) from 800 to 1200 Pa. Creep curves obtained with an application of a shear stress of 30 Pa were viscoelastic in nature. The G ₀ and η values were, respectively, 1.4 ± 0.3 × 10³ Pa and 3.3 ± 0.65 × 10⁶ Pa s. The relationship between the characteristics of NF biofilms and the flow conditions encountered during NF is discussed.     

Calorimetrie Study of Escherichia coli Growth on Bouillon Medium

Heat evolution during the growth of Escherichia coli in a stationary culture on bouillon medium was continuously monitored with a conduction-type batch calorimeter at different pHs and temperatures. The growth thermograms were found to be reproducible within percent errors of ±2.1%, ±0.8% and ±1.5% for the peak time of a thermogram, the peak height and the total heat evolution, respectively. The mean heat evolution for the formation of a unit E. coli cell was co = (1.69 ±0.08) X 10^—8 J cell^{— 1} at pH 6.2 and 37°C. The mean heat evolution rate per unit cell during growth was </ = 3.6ρwcell^_1, which was consistent with values calculated for other microbial cells. The growth rate constant calculated on kinetic analysis of the growth thermograms was μ = 0.532 ± 0.068 hr ^-1 at pH 6.2 and 37°C. The pH dependence of the growth rate constant showed that the growth activity of E. coli cells on bouillon medium is maximum in the pH range of 5.5 to 6.5. From the temperature-dependent variations in the growth rate constant, the apparent activation energy of E. coli growth was found to be E_a =65.3 ±7.1 kJ mol^-1.     

Vibration settling time of the gastrocnemius remains constant during an exhaustive run in rear foot strike runners

In this study, vibrations of human gastrocnemius during an exhaustive run protocol are considered for analysis. Previous studies have shown increased vibration intensity and damping coefficient within the soft tissue with fatigue. The question of this study was to investigate if the vibration settling time remains constant during a prolonged running. Eleven semi-professional middle/long distance runners ran to exhaustion on a treadmill with their preferred constant speed (4.29 ± 0.33 m/s) for 3873 ± 1147 m. Vibration of the gastrocnemius lateralis, electrical activity of the tibialis anterior and the gastrocnemius medialis along with ground reaction force (GRF) were recorded. The results demonstrated significant increase in impact peak and loading rate, and the frequency content of the impact, with no significant change in active peak of the vertical GRF. Fatigue resulted in increased vibration intensity, damping coefficient, and energy dissipation of vibration with no change in vibration settling time. Furthermore, peak acceleration significantly linearly (R = 0.59) increased as a function of running time. The mean frequency of muscle activity of the gastrocnemius medialis and the intensity of muscle activity in TA significantly decreased. The results suggest that constant vibration settling time might either be an objective for muscle tuning which is more pronounced in fatigued state or a passive by-product of muscle function in running. Further studies are needed to address this point.     

In vitro catabolic effect of protoporphyrin IX in human osteoblast-like cells: possible role of the 18 kDa mitochondrial translocator protein

In several pathological conditions, when conversion of Protoporphyrin (PP)IX into heme is impaired, a toxic accumulation of PPIX might occur. PPIX has been found to have affinity to the mitochondrial Translocator Protein 18 kDa. Since it is known that TSPO is abundant in human osteoblast cells, thus we assumed that PPIX can affect cellular functions via interactions with TSPO in these cells. Therefore we aimed to study the metabolic responses of human osteoblast to a high (10^?5M) concentration of PPIX in vitro. We found that in primary culture of human osteoblast-like cells cell numbers decreased following exposure to PPIX(10^?5M). Cellular [¹⁸F]-FDG incorporation, mitochondrial mass, ATP content were suppressed, and ΔΨm collapsed. Lactate dehydrogenase activity was enhanced in culture media, indicating overall cell death, while no increase in apoptotic levels was observed. Cellular proliferation was not affected. Protein expression of TSPO, VDAC 1, and hexokinase 2 decreased, although the synthesis of mRNA for hexokinase 2 increased. Thus, PPIX(10^?5M) has a cytotoxic effect on human osteoblast-like cell in vitro. Since these cells remain viable following exposure to another TSPO ligand, PK 11195 (10^?5M), as observed previously by us, the mode of action of PPIX on osteoblast-like cells is not identical to that of PK 11195. Accordingly pathological accumulation of PPIX may cause necrosis of osteoblasts leading to bone mass loss. We show that this phenomenon is unrelated to iron overload.     

Cooperative nonenzymic base recognition. Kinetics of the binding of a base monomer to a complementary polynucleotide template

The kinetics of double-helix formation by poly U and the complementary monomer N-6,9-dimethyladenine (m⁶m⁹A) has been measured using a new fast temperature-jump apparatus. The cooperative binding kinetics are complicated by the extensive self-association of the monomers, but a satisfactory analysis using average relaxation times was possible in terms of three different models. Application of a model which considers only monomer binding yields the upper limit for the binding rate constant of an m⁶m⁹A monomer next to an already bound monomer on a poly U strand: (2 ± 0.4) × 10⁸ M^?1sec^?1. A lower limit is found by using a model which allows for binding of all m⁶m⁹A stacks to poly U with equal rate constants: (3 ± 0.3) × 10⁷ M^?1sec^?1. A third model with “weighted” rate constants consistent with the data: (7.5 ± 1.0) × 10⁷ M^?1sec^?1. The rate of cooperative binding of m⁶m⁹A to the trimer UpUpU has also been measured. The rate constants obtained with the trimer agree with those obtained with the polymer for each of the three models within experimental error.     

Collection and fertilization potential of sperm from the Sulawesi crested black macaque (Macaca nigra)

In this study, semen was obtained by rectal probe electrostimulation (RPE) from the Sulawesi crested black macaque (Macaca nigra). Three experimental series were conducted. First, semen was collected from four animals anesthetized with either tiletamine-zolazepam (Telazol®) or ket-amine-HCl (Vetalar®) (five collections from each animal with each drug). Because of greater muscle relaxation and analgesia, we found tiletaminezolazepam to be an attractive alternative to ketamine-HCl as an anesthetic agent for RPE in M. nigra. Second, semen was collected from another four animals at stimulation frequencies of either 30 Hz or 60 Hz (five collections from each animal at each frequency). There were no significant differences in sperm number, in percentage of sperm with progressive motility, in the current required for sample recovery between tiletamine-zolazepam or ketamine-HCl anesthesia, or between a 30 Hz or 60 Hz stimulation frequency. Third, to check for retrograde sperm loss, the bladders of four animals were emptied, flushed with sterile saline, and then infused with TALP-Hepes medium. After RPE, sperm numbers in the bladder were compared with those in the ejaculate. Although sperm were recovered from the bladder [1.6 (± 0.9) × 10⁶] (mean ± SEM), the numbers were significantly less (P < 0.05) than those in the ejaculate [49 (± 18) × 10⁶]. The percentage of sperm with normal morphology in these samples was high (96.8 ± 1.0%). The average sperm number in the 84 samples collected for this study was 33.8 (± 4.1) × 10⁶. In preliminary experiments, we found that M. nigra sperm will fertilize rhesus monkey oocytes (Macaca mulatta) in vitro. © 1992 Wiley-Liss, Inc.     

Reconstitution of a Regulated Transepithelial Water Pathway in Cells Transfected with AQP2 and an AQP1/AQP2 Hybrid Containing the AQP2-C Terminus

Transepithelial water permeability was measured in LLC-PK1 cells stably transfected with aquaporins (AQPs): AQP1, AQP2, and a chimera of AQP1 and AQP2 containing 41 amino acids of the C-terminus of AQP2. Transepithelial water fluxes (Jw) were not previously reported in cells transfected with aquaporins. Jw were now recorded each minute using a specially developed experimental device. A significant increase in Posm after forskolin (FK) plus vasopressin (VP) was found in AQP2 transfected cells (39.9 ± 8.2 vs. 12.5 ± 3.3 cm · sec⁻¹· 10⁻³), but not in cells transfected with AQP1 (15.3 ± 3.6 vs. 13.4 ± 3.6 cm · sec⁻¹· 10⁻³). In the case of the AQP1/2 cells (chimera) the FK plus VP induced Posm was smaller than in AQP2 cells but significantly higher than in mock cells at rest (18.1 ± 4.8 vs. 6.7 ± 1.0 cm · sec⁻¹· 10⁻³). The increases in Posm values were not paralleled by increases in ¹⁴C-Mannitol permeability. HgCl₂ inhibited the hydrosmotic response to FK plus VP in AQP2 transfected epithelia. Results were comparable to those observed, in parallel experiments, in a native ADH-sensitive water channel containing epithelial barrier (the toad urinary bladder). Electron microscopy showed confluent LLC-PK1 cells with microvilli at the mucosal border. The presence of spherical or elongated intracellular vacuoles was observed in AQP2 transfected cells, specially after FK plus VP stimulus and under an osmotic gradient. These results demonstrate regulated transepithelial water permeability in epithelial cells transfected with AQP2. Received: 24 June 1997/Revised: 16 September 1997     

Quantitative assessment of dielectric parameters for membrane lipid bi‐layers from RF permittivity measurements

In this article, we propose and validate theoretical and experimental methods to quantitatively assess the Debye dielectric model of membrane lipid bi‐layers. This consists of two steps: permittivity measurements of biological solutions (liposomes), and estimation of the model parameters by inverse application of the Effective Medium Theory. The measurements are conducted in the frequency domain between 100 MHz and 2 GHz using a modified coaxial connector, at the temperatures of 27 and 30 °C. Estimations have been performed using a three‐layered model based on the Maxwell–Wagner formulation. Debye parameters (mean value ± standard error) found from fitting experimental data are: ε_s = 11.69 ± 0.09, ε_∞ = 4.00 ± 0.07, f_relax = 179.85 ± 6.20 MHz and ε_s = (1.1 ± 0.1) × 10^?7 S/m. This model can be used in microdosimetric studies aiming to precisely determine the E‐field distribution in a biological target down to the single cell level. In this context the use of an accurate membrane dielectric model, valid through a wide frequency range, is particularly appropriate. Bioelectromagnetics 30:286–298, 2009. © 2009 Wiley‐Liss, Inc.     

A Soft and Robust Spring Based Triboelectric Nanogenerator for Harvesting Arbitrary Directional Vibration Energy and Self‐Powered Vibration Sensing

Vibration is a common mechanical phenomenon and possesses mechanical energy in ambient environment, which can serve as a sustainable source of power for equipment and devices if it can be effectively collected. In the present work, a novel soft and robust triboelectric nanogenerator (TENG) made of a silicone rubber‐spring helical structure with nanocomposite‐based elastomeric electrodes is proposed. Such a spring based TENG (S‐TENG) structure operates in the contact‐separation mode upon vibrating and can effectively convert mechanical energy from ambient excitation into electrical energy. The two fundamental vibration modes resulting from the vertical and horizontal excitation are analyzed theoretically, numerically, and experimentally. Under the resonant states of the S‐TENG, its peak power density is found to be 240 and 45 mW m^?2 with an external load of 10 MΩ and an acceleration amplitude of 23 m s^?2. Additionally, the dependence of the S‐TENG's output signal on the ambient excitation can be used as a prime self‐powered active vibration sensor that can be applied to monitor the acceleration and frequency of the ambient excitation. Therefore, the newly designed S‐TENG has a great potential in harvesting arbitrary directional vibration energy and serving as a self‐powered vibration sensor.     

Response of <Emphasis Type="Italic">Camptotheca acuminata</Emphasis> calli stimulated by mechanical vibration

Plants in their natural environment are usually affected by mechanical stress because of their sessile growth habit. This work was aimed at determining the effects of mechanical vibration on the growth rate, physiological indexes, and secondary metabolite biosynthesis of Camptotheca acuminata calli. In this study, mechanical vibrations of 1–4 Hz in frequency were applied to stimulate the C. acuminata calli; we found that a mechanical vibration of moderate frequency (2 Hz) can clearly promote the growth rate and increase the soluble protein content and superoxide dismutase (SOD) activity. Under a mechanical vibration of a 2 Hz frequency, camptothecin (CPT), the main secondary metabolite produced by C. acuminata, was increased by about fourfold compared to the control group, In contrast, the increased accumulation disappears at higher frequencies. The optimal vibration time for obtaining the highest levels of biomass and CPT was 60 min. This study showed that there are neutral frequencies and optimal periods of mechanical vibration on C. acuminata calli.     

A pivotal role of bone remodeling in granulocyte colony stimulating factor induced hematopoietic stem/progenitor cells mobilization

The majority of hematopoietic stem/progenitor cells (HSPCs) reside in bone marrow (BM) surrounded by a specialized environment, which governs HSPC function. Here we investigated the potential role of bone remodeling cells (osteoblasts and osteoclasts) in homeostasis and stress‐induced HSPC mobilization. Peripheral blood (PB) and BM in steady/mobilized state were collected from healthy donors undergoing allogeneic transplantation and from mice treated with granulocyte colony stimulating factor (G‐CSF), parathyroid hormone (PTH), or receptor activator of nuclear factor kappa‐B ligand (RANKL). The number and the functional markers of osteoblasts and osteoclasts were checked by a series of experiments. Our data showed that the number of CD45^?Ter119^? osteopontin (OPN)⁺ osteoblasts was significantly reduced from 4,085 ± 135 cells/femur on Day 0 to 1,032 ± 55 cells/femur on Day 5 in mice (P = 0.02) and from 21.38 ± 0.66 on Day 0 to 14.78 ± 0.65 on Day 5 in healthy donors (P < 0.01). Decrease of osteoblast number leads to reduced level of HSPC mobilization regulators stromal cell‐derived factor‐1 (SDF‐1), stem cell factor (SCF), and OPN. The osteoclast number at bone surface (OC.N/B.s) was significantly increased from 1.53 ± 0.12 on Day 0 to 4.42 ± 0.46 on Day 5 (P < 0.01) in G‐CSF‐treated mice and from 0.88 ± 0.20 on Day 0 to 3.24 ± 0.31 on Day 5 (P < 0.01) in human. Serum TRACP‐5b level showed a biphasic trend during G‐CSF treatment. The ratio of osteoblasts number per bone surface (OB.N/B.s) to OC.N/B.s was changed after adding PTH plus RANKL during G‐CSF treatment. In conclusion, short term G‐CSF treatment leads to reduction of osteoblasts and stimulation of osteoclasts, and interrupting bone remodeling balance may contribute to HSPC mobilization. J. Cell. Physiol. © 2012 Wiley Periodicals, Inc.     

Multiple activation of mouse sperm motility

To investigate the activation mechanism of mouse sperm motility, the intact sperm in various activities were further investigated after demembranation. When dry sperm was diluted into sucrose solution, the sperm exhibited low motility with the swimming velocity of 13.5 ± 3.8 μm/s and the beat frequency of 1.5 ± 0.4 Hz. The demembranated sperm were immotile in the reactivation solution lacking cAMP. Meanwhile, when dry sperm was diluted into the solution containing either high concentration of NaCl or Ca²⁺, they exhibited the beat frequency of about 9 Hz. The demembranated ones exhibited the intermediate motility in the absence of cAMP. When dry sperm were diluted into the sucrose solution containing HCO₃, the sperm exhibited a vigorous motility with the swimming velocity of 181.2 ± 10.1 μm/s and the beat frequency of 11.3 ± 1.2 Hz. The demembranated sperm exhibited the high reactivation motility (90%) and flagellar beat frequency (9 Hz) in the absence of cAMP. These values were almost equivalent to those obtained in the demembranated sperm pretreated with sucrose or Ca²⁺ or NaCl and reactivated in the presence of cAMP. The activation induced by bicarbonate was considered complete in comparison with the activation by Ca²⁺ or NaCl. It was likely that the activation of mouse sperm motility took multiple states. © 1993 Wiley-Liss, Inc.     

Ranolazine inhibits shear sensitivity of endogenous Na+ current and spontaneous action potentials in HL-1 cells

Na_V1.5 is a mechanosensitive voltage-gated Na⁺ channel encoded by the gene SCN5A, expressed in cardiac myocytes and required for phase 0 of the cardiac action potential (AP). In the cardiomyocyte, ranolazine inhibits depolarizing Na⁺ current and delayed rectifier (I_Kr) currents. Recently, ranolazine was also shown to be an inhibitor of Na_V1.5 mechanosensitivity. Stretch also accelerates the firing frequency of the SA node, and fluid shear stress increases the beating rate of cultured cardiomyocytes in vitro. However, no cultured cell platform exists currently for examination of spontaneous electrical activity in response to mechanical stimulation. In the present study, flow of solution over atrial myocyte-derived HL-1 cultured cells was used to study shear stress mechanosensitivity of Na⁺ current and spontaneous, endogenous rhythmic action potentials. In voltage-clamped HL-1 cells, bath flow increased peak Na⁺ current by 14 ± 5%. In current-clamped cells, bath flow increased the frequency and decay rate of AP by 27 ± 12% and 18 ± 4%, respectively. Ranolazine blocked both responses to shear stress. This study suggests that cultured HL-1 cells are a viable in vitro model for detailed study of the effects of mechanical stimulation on spontaneous cardiac action potentials. Inhibition of the frequency and decay rate of action potentials in HL-1 cells are potential mechanisms behind the antiarrhythmic effect of ranolazine.