Soleus biopsies were obtained from four male astronauts 45 days before and within 2 h after a 17 day spaceflight. For all astronauts, single chemically skinned post‐flight fibres expressing only type I myosin heavy chain (MHC) developed less average peak Ca2+ activated force (Po) during fixed‐end contractions (0.78 ± 0.02 vs. 0.99 ± 0.03 mN) and shortened at a greater mean velocity during unloaded contractions (Vo) (0.83 ± 0.02 vs. 0.64 ± 0.02 fibre lengths s−1) than pre‐flight type I fibres. The flight‐induced decline in absolute Po was attributed to reductions in fibre diameter and/or Po per fibre cross‐sectional area. Fibres from the astronaut who experienced the greatest relative loss of peak force also displayed a reduction in Ca2+ sensitivity. The elevated Vo of the post‐flight slow type I fibres could not be explained by alterations in myosin heavy or light chain composition. One alternative possibility is that the elevated Vo resulted from an increased myofilament lattice spacing. This hypothesis was supported by electron micrographic analysis demonstrating a reduction in thin filament density post‐flight. Post‐flight fibres shortened at 30 % higher velocities than pre‐flight fibres at external loads associated with peak power output. This increase in shortening velocity either reduced (2 astronauts) or prevented (2 astronauts) a post‐flight loss in fibre absolute peak power (μN (fibre length) s−1). The changes in soleus fibre diameter and function following spaceflight were similar to those observed after 17 days of bed rest. Although in‐flight exercise countermeasures probably reduced the effects of microgravity, the results support the idea that ground‐based bed rest can serve as a model of human spaceflight. In conclusion, 17 days of spaceflight decreased force and increased shortening velocity of single Ca2+‐activated muscle cells expressing type I MHC. The increase in shortening velocity greatly reduced the impact that impaired force production had on absolute peak power.

Ion current rectification with quartz nanopipette electrodes was investigated through the control of the surface charge. The presence and absence of a positively charged poly-L-lysine (PLL) coating resulted in the rectified current with opposite polarity. The results agreed with the theories developed for current-rectifying conical nanopores, suggesting the similar underlying mechanism among asymmetric nanostructure in general. This surface condition dependence can be used as the fundamental principle of multi-purpose real-time in vivo biosensors. Nanomaterials are being widely exploited by recent technologies because of their extraordinary properties. Although the development of fabrication processes for particular nanostructures poses great challenges by itself, the practical use of these nanomaterials is also of great interest for biology and medicine. 1 Because of their structural diversity, these materials are often categorized and referred to as nanoparticles, 2 nanowires, 3 nanotubes, 4 nanopores, 5 or nanopatterned surfaces. 6 Nanopipettes are among these; a nanopipette is defined as a pipette with a very fine tip that has a nanoscale opening. Nanolithography is one of the typical applications of nanopipettes as a delivery tool of a tiny amount of chemicals. 7,8 Nanopipettes are versatile enough to be used as a tool for sensitive detection in biomedical applications. Optical detection of fluorescently labeled macromolecules such as DNA or proteins with nanopipettes has been reported. 9,10 Fully electrical detection has also been shown with similarly sized nanoparticles, whose flow through the nanopipette opening creates temporal current blockades. 11 The ultimate goal of these efforts, the label-free real-time electrical detection of single molecules, could be achieved eventually by a deeper understanding of the fundamental characteristics of nanopipette electrodes under an external electric field. It not only helps to unveil the dynamics of biological systems but can also have a remarkable impact on drug screening and pathogen detection. Interestingly, although a general understanding of nanopipette electrodes can be based on the understanding of microelectrodes, the unique nanoscale geometry often causes characteristic behavior that requires further focused studies. For example, related studies have examined the physicochemical properties of nanopipettes under varying conditions such as electrolyte concentrations and pH, 12 or polyethylene glycol polymer coatings. 13 Similarly shaped goldplated conical nanopores have been studied in a more detailed manner, involving observations of the role of surface charge in the ionic current. 14 Our target here is the effect of cationic polymer coating on a glass nanopipette surface, providing the basis for functionalized nanopipettes that will be used as sensitive biosensors. By understanding how ions flow through the nanometer-sized opening, how these ions interact with the surface inside and outside the tip, and what happens if the surface is modified by...

Single DNA molecules labeled with nanoparticles can be detected by blockades of ionic current as they are translocated through a nanopipette tip formed by a pulled glass capillary. The nanopipette detection technique can provide not only tools for detection and identification of single DNA and protein molecules but also deeper insight and understanding of stochastic interactions of various biomolecules with their environment.

Nanopipette technology can uniquely identify biomolecules such as proteins based on differences in size, shape, and electrical charge. These differences are determined by the detection of changes in ionic current as the proteins interact with the nanopipette tip coated with probe molecules. Here we show that electrostatic, biotin-streptavidin, and antibody-antigen interactions on the nanopipette tip surface affect ionic current flowing through a 50-nm pore. Highly charged polymers interacting with the glass surface modulated the rectification property of the nanopipette electrode. Affinity-based binding between the probes tethered to the surface and their target proteins caused a change in the ionic current due to a partial blockade or an altered surface charge. These findings suggest that nanopipettes functionalized with appropriate molecular recognition elements can be used as nanosensors in biomedical and biological research.biomolecules ͉ biosensor ͉ immunoassay ͉ current rectification ͉ nanopore N anopipettes, characterized by the submicron to nanoscale size of the pore at the tip, are of great interest because of their unique physicochemical properties and potential for various biomedical and biological applications. By pulling a single glass capillary, one can easily and cost-effectively create a pair of nanopipettes that can be used for molecular deposition onto a solid surface (1, 2), for delivery to the surface of a single cell (3) and its inner compartments (4, 5), or for biomolecular sensing as described hereafter. These applications can be optimized by an enhanced understanding of the physical and chemical interactions at the pore region, which has been a subject of theoretical studies (6). Advances in both technical and theoretical fronts will further demonstrate the utility of nanopipettebased devices for many purposes.Biomolecule sensing with a nanopipette probe has been performed with and without the aid of optical methods. Fluorescence-based pH sensing (7) shows the submicron spatial resolution and millisecond time resolution of such sensors. Fully-electrical detection of DNA-conjugated gold nanoparticles (8) uses resistive pulses caused by the translocation of fairly large (10 nm) particles, the underlying principle identical to that of nanopore biosensors (9) and DNA sequencers (10). Unlike other nanostructure-based chemical sensors (11), which often require access to semiconductor facilities, nanopipette biosensors can be created and tailored at the bench, thereby reducing turnaround time. Nanopipettes also have enormous potential for detecting a small number of molecules from a tiny amount of clinical samples or live single cells, a feature useful for medical diagnostics and molecular and cellular biology research.A key challenge for nanopipette biosensors is adapting to applications where specific molecules can be targeted. One approach would be to separate the sensing and actuating functions, an idea embodied by an engineered ion channel fused with a surface receptor protein responsible f...

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Soleus muscle fibers from the rat display a reduction in peak power and Ca2+ sensitivity after hindlimb suspension. To examine human responses to non-weight bearing, we obtained soleus biopsies from eight adult men before and immediately after 17 days of bed rest (BR). Single chemically skinned fibers were mounted between a force transducer and a servo-controlled position motor and activated with maximal (isotonic properties) and/or submaximal (Ca2+ sensitivity) levels of free Ca2+. Gel electrophoresis indicated that all pre- and post-BR fibers expressed type I myosin heavy chain. Post-BR fibers obtained from one subject displayed increases in peak power and Ca2+ sensitivity. In contrast, post-BR fibers obtained from the seven remaining subjects showed an average 11% reduction in peak power (P < 0.05), with each individual displaying a 7-27% reduction in this variable. Post-BR fibers from these subjects were smaller in diameter and produced 21% less force at the shortening velocity associated with peak power. However, the shortening velocity at peak power output was elevated 13% in the post-BR fibers, which partially compensated for their lower force. Post-BR fibers from these same seven subjects also displayed a reduced sensitivity to free Ca2+ (P < 0.05). These results indicate that the reduced functional capacity of human lower limb extensor muscles after BR may be in part caused by alterations in the cross-bridge mechanisms of contraction.

It is well known that skeletal muscle intrinsic maximal shortening velocity is inversely related to species body mass. However, there is uncertainty regarding the relationship between the contractile properties of muscle fibers obtained from commonly studied laboratory animals and those obtained from humans. In this study we determined the contractile properties of single chemically skinned fibers prepared from rat, rhesus monkey, and human soleus and gastrocnemius muscle samples under identical experimental conditions. All fibers used for analysis expressed type I myosin heavy chain as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Allometric coefficients for type I fibers from each muscle indicated that there was little change in peak tension (force/fiber cross-sectional area) across species. In contrast, both soleus and gastrocnemius type I fiber maximal unloaded shortening velocity (Vo), the y-intercept of the force-velocity relationship (Vmax), peak power per unit fiber length, and peak power normalized for fiber length and cross-sectional area were all inversely related to species body mass. The present allometric coefficients for soleus fiber Vo (-0.18) and Vmax (-0.11) are in good agreement with published values for soleus fibers obtained from common laboratory and domesticated mammals. Taken together, these observations suggest that the Vo of slow fibers from quadrupeds and humans scale similarly and can be described by the same quantitative relationships. These findings have implications in the design and interpretation of experiments, especially those that use small laboratory mammals as a model of human muscle function.

A B S TRACT To understand the nature of the transmission process of excitationcontraction (EC) coupling, the effects of the anion perchlorate were investigated on the voltage sensor (dihydropyridine receptor, DHPR) and the Ca release channel (ryanodine receptor, RyR) of the sarcoplasmic reticulum (SR). The molecules, from rabbit skeletal muscle, were either separated in membrane vesicular fractions or biochemically purified so that the normal EC coupling interaction was prevented. Additionally, the effect of CIO~ was investigated on L-type Ca 2+ channel gating currents of guinea pig ventricular myocytes, as a native DHPR not in the physiological interaction of skeletal muscle. At 20 raM, CIO 4 had minor effects on the activation of ionic currents through Ca channels from skeletal muscle transverse tubular (T) membranes fused with planar bilayers: a +7-mV shift in the midpoint voltage, ~', with no change in kinetics of activation or deactivation. This is in contrast with the larger, negative shift that CIO 4 causes on the distribution of intramembrane charge movement of skeletal muscle. At up to 100 mM it did not affect the binding of the DHP [~H]PN200-110 to triad-enriched membrane fractions (TR). At 8 mM it did not affect the kinetics or the voltage distribution of gating currents of Ca channels in heart myocytes. These negative results were in contrast to the effects of C10 4 on the release channel. At 20 mM it increased several-fold the open probability of channels from purified RyR incorporated in planar bilayers and conducting Ba z+, an effect seen on channels first closed by chelation of Ca 2+ or by the presence of Mg 2+. It significantly increased the initial rate of efflux of 45Ca2+ from TR vesicles (by a factor of 1.75 at 20 mM and 4.5 at 100 mM). I-increased the association rate constant to a similar extent. The binding of ryanodine to purified RyR protein reconstituted into liposomes had a greater affinity than to TR fractions but was similarly enhanced by C10;. The reducing agent dithiothreitol (5 mM) did not reduce the effect of CIO 4, and 5% polyethylene glycol, with an osmolarity equivalent to 20 mM C10;, did not change ryanodine binding. The results are consistent with a primary effect of CIO4 on the release channel and suggest that the effect on charge movement may be secondary, mediated by a mechanical interaction between the voltage sensor and the release channel.