The osmotic and permeability parameters of a cell membrane are essential physico-chemical properties of a cell and particularly important with respect to cell volume changes and the regulation ...thereof. Here, we report the hydraulic conductivity, L(p), the non-osmotic volume, V(b), and the Arrhenius activation energy, E(a), of mammalian COS-7 cells. The ratio of V(b) to the isotonic cell volume, V(c iso), was 0.29. E(a), the activation energy required for the permeation of water through the cell membrane, was 10,700, and 12,000 cal/mol under hyper- and hypotonic conditions, respectively. Average values for L(p) were calculated from swell/shrink curves by using an integrated equation for L(p). The curves represented the volume changes of 358 individually measured cells, placed into solutions of nonpermeating solutes of 157 or 602 mOsm/kg (at 0, 10 or 22°C) and imaged over time. L(p) estimates for all six combinations of osmolality and temperature were calculated, resulting in values of 0.11, 0.21, and 0.10 µm/min/atm for exosmotic flow and 0.79, 1.73 and 1.87 µm/min/atm for endosmotic flow (at 0, 10 and 22°C, respectively). The unexpected finding of several fold higher L(p) values for endosmotic flow indicates highly asymmetric membrane permeability for water in COS-7. This phenomenon is known as rectification and has mainly been reported for plant cell, but only rarely for animal cells. Although the mechanism underlying the strong rectification found in COS-7 cells is yet unknown, it is a phenomenon of biological interest and has important practical consequences, for instance, in the development of optimal cryopreservation.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
We have developed a simple, inexpensive system (<$300 US) for measuring cooling and warming rates of small (∼ 0.1
μl) aqueous samples at rates as high as 10
5
°C/min. The measurement system itself, ...can track rates approaching one million
°C/min. For temperature sensing, a Type T thermocouple with 50
μm wire was used. The thermocouple output voltage was read with an inexpensive USB based digital oscilloscope interfaced to a laptop computer, and the raw data were processed with MS Excel.
Scour holes often form in shallow flows over sand on the beach and in morphodynamic scale experiments of river reaches, deltas and estuarine landscapes. The scour holes are on average 2 cm deep and ...5 cm long, regardless of the flow depth and appear to occur under similar conditions as current ripples: at low boundary Reynolds numbers, in fine sand and under relatively low sediment mobility. In landscape experiments, where the flow is only about 1 cm deep, such scours may be unrealistically large and have unnatural effects on channel formation, bar pattern and stratigraphy. This study tests the hypotheses that both scours and ripples occur in the same conditions and that the roughness added by sediment saltation explains the difference between the ripple–dune transition and the clear‐water hydraulic smooth to rough transition. About 500 experiments are presented with a range of sediment types, sediment mobility and obstructions to provoke scour holes, or removal thereof to assess scour hole persistence. Most experiments confirm that ripples and scour holes both form in the ripple stability field in two different bedform stability diagrams. The experiments also show that scours can be provoked by perturbations even below generalized sediment motion. Moreover, the hydraulic smooth to rough transition modified with saltation roughness depending on sediment mobility was similar in magnitude and in slope to ripple–dune transitions. Given uncertainties in saltation relations, the smooth to rough transitions modified for movable beds are empirically equivalent to the ripple–dune transitions. These results are in agreement with the hypothesis that scours form by turbulence caused by localized flow separation under low boundary Reynolds numbers, and do not form under generalized flow separation over coarser particles and intense sediment saltation. Furthermore, this suggests that ripples are a superposition of two independent forms: periodic bedforms occurring in smooth and rough conditions plus aperiodic scours occurring only in hydraulic smooth conditions.
Successful cryopreservation of mammalian cells requires rapid transport of water and cryoprotective solutes across the plasma
membrane. Aquaporin-3 is known as a water/solute channel that can ...transport water and neutral solutes such as glycerol. In
this study we examined whether artificial expression of aquaporin-3 in mouse oocytes can improve water and glycerol permeability
and oocyte survival after cryopreservation. Immature mouse oocytes were injected with aquaporin-3 cRNA and were cultured for
12 h. Then the hydraulic conductivity (L P ) and glycerol permeability (P GLY ) of matured oocytes were determined from the relative volume changes in 10% glycerol in PB1 medium at 25°C. Mean ± SD values
of L P and P GLY of cRNA-injected oocytes (3.09 ± 1.22 μm min â1 atm â1 and 3.69 ± 1.47 à 10 â3 cm/min, respectively; numbers of oocytes = 25) were significantly higher than those of noninjected oocytes (0.83 ± 0.02 μm
min â1 atm â1 and 0.07 ± 0.02 à 10 â3 cm/min, respectively; n = 13) and water-injected oocytes (0.87 ± 0.10 μm min â1 atm â1 and 0.08 ± 0.02 à 10 â3 cm/min, respectively; n = 20). After cryopreservation in a glycerol-based solution, 74% of cRNA-injected oocytes (n = 27)
survived as assessed by their morphological appearance, whereas none of the water-injected oocytes survived (n = 10). When
cRNA-injected oocytes that survived cryopreservation were inseminated in vitro, the penetration rate was 40% (n = 48) and
the cleavage rate was 31% (n = 70), showing that oocytes retain their ability to be fertilized. This is the first report to
show that artificial expression of a water/solute channel in a cell improves its survival after cryopreservation. This approach
may enable cryopreservation of cells that have been difficult to cryopreserve.
Hydromorphological data for many estuaries worldwide is scarce and usually limited to offshore tidal amplitude and remotely-sensed imagery. In many projects, information about morphology and ...intertidal area is needed to assess the effects of human interventions and rising sea-level on the natural depth distribution and on changing habitats. Habitat area depends on the spatial pattern of intertidal area, inundation time, peak flow velocities and salinity. While numerical models can reproduce these spatial patterns fairly well, their data need and computational costs are high and for each case a new model must be developed. Here, we present a Python tool that includes a comprehensive set of relations that predicts the hydrodynamics, bed elevation and the patterns of channels and bars in mere seconds. Predictions are based on a combination of empirical relations derived from natural estuaries, including a novel predictor for cross-sectional depth distributions, which is dependent on the along-channel width profile. Flow velocity, an important habitat characteristic, is calculated with a new correlation between depth below high water level and peak tidal flow velocity, which was based on spatial numerical modelling. Salinity is calculated from estuarine geometry and flow conditions. The tool only requires an along-channel width profile and tidal amplitude, making it useful for quick assessments, for example of potential habitat in ecology, when only remotely-sensed imagery is available.
Fluvial–tidal transitions in estuaries are used as major shipping fairways and are characterised by complex bar and channel patterns with a large biodiversity. Habitat suitability assessment and the ...study of interactions between morphology and ecology therefore require bathymetric data. While imagery offers data of planform estuary dimensions, only for a few natural estuaries are bathymetries available. Here we study the empirical relation between along-channel planform geometry, obtained as the outline from imagery, and hypsometry, which characterises the distribution of along-channel and cross-channel bed levels. We fitted the original function of Strahler (1952) to bathymetric data along four natural estuaries. Comparison to planform estuary shape shows that hypsometry is concave at narrow sections with large channels, while complex bar morphology results in more convex hypsometry. We found an empirical relation between the hypsometric function shape and the degree to which the estuary width deviates from an ideal convergent estuary, which is calculated from river width and mouth width. This implies that the occurring bed-level distributions depend on inherited Holocene topography and lithology. Our new empirical function predicts hypsometry and along-channel variation in intertidal and subtidal width. A combination with the tidal amplitude allows for an estimate of inundation duration. The validation of the results on available bathymetry shows that predictions of intertidal and subtidal area are accurate within a factor of 2 for estuaries of different size and character. Locations with major human influence deviate from the general trends because dredging, dumping, land reclamation and other engineering measures cause local deviations from the expected bed-level distributions. The bathymetry predictor can be used to characterise and predict estuarine subtidal and intertidal morphology in data-poor environments.
Phase diagrams are of great utility in cryobiology, especially, those consisting of a cryoprotective agent (CPA) dissolved in a physiological salt solution. These ternary phase diagrams consist of ...plots of the freezing points of increasing concentrations of solutions of cryoprotective agents (CPA) plus NaCl. Because they are time-consuming to generate, ternary diagrams are only available for a small number of CPAs. We wanted to determine whether accurate ternary phase diagrams could be synthesized by adding together the freezing point depressions of binary solutions of CPA/water and NaCl/water which match the corresponding solute molality concentrations in the ternary solution. We begin with a low concentration of a solution of CPA
+
salt of given
R (CPA/salt) weight ratio. Ice formation in that solution is mimicked by withdrawing water from it which increases the concentrations of both the CPA and the NaCl. We compute the individual solute concentrations, determine their freezing points from published binary phase diagrams, and sum the freezing points. These yield the synthesized ternary phase diagram for a solution of given
R. They were compared with published experimental ternary phase diagrams for glycerol, dimethyl sulfoxide (DMSO), sucrose, and ethylene glycol (EG) plus NaCl in water. For the first three, the synthesized and experimental phase diagrams agreed closely, with some divergence occurring as wt% concentrations exceeded 30% for DMSO and 55% for glycerol, and sucrose. However, in the case of EG there were substantial differences over nearly the entire range of concentrations which we attribute to systematic errors in the experimental EG data. New experimental EG work will be required to resolve this issue.
Estuaries show dynamic patterns of channels and bars, which are also valuable habitats, while channels provide access to harbours. In contrast with bars in rivers, we still lack explanations, theory ...and classifications for bars in estuaries. Theories for river bars show bar properties to be strongly dependent on channel width-to-depth ratio. For estuaries, only two physics-based theories are available. One predicts bar length to increase with flow velocity and tidal excursion length and the other with flow velocity and estuary width. However, these theories have not been tested for lack of data and experiments. Our objective is to determine bar shape and dimensions in funnel shaped alluvial estuaries and to provide predictive relations for bar shapes and dimensions. We present a new dataset measured in imagery and bathymetry with bar lengths spanning from centimetres (in experiments) to tens of kilometres. We visually identified and classified 190 bars and measured their width, length, height and number of cross-cutting barbs channels. Estuarine geometry and tidal characteristics were obtained from available databases and literature. We found that many compound bars can be seen as simple linear bars partly cut by barb channels, where partitioning of bar width collapses the data of bar length-to-width ratio. This is in agreement with the transverse wave form of bars assumed in linear stability theories that are supported by data in fluvial and coastal environments. Our empirical trend shows that sand bars in estuaries have similar length-to-width ratios as river bars but are more elongated. This trend was also found to hold for bars in numerical models and scaled laboratory experiments. Bar height is linearly related to local water depth. Natural bar length, bar width and braiding index are strongly correlated to estuary width. This relation is also evident in published data of bars in rivers and numerical models of rivers. The theoretical braiding index of tidal bars indeed depends on local width-to-depth ratio and is reasonably well predicted for our dataset. However, the theoretical models for tidal bar wave length and width surprisingly lack this correlation with estuary width and overpredict by an order of magnitude, pointing at a need to revisit tidal bar theory. The empirical relations provide a means of estimating bar dimensions when limited data are available and in order to evaluate results from numerical models and physical experiments.
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