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101.
Functional differences between two classes of sodium channels in developing rat skeletal muscle 总被引:10,自引:0,他引:10
Excitability is generated in developing skeletal muscle by the incorporation of sodium-selective ion channels into the surface membrane. Whole-cell and patch voltage-clamp recording from myotubes and their embryologic precursors, myoblasts, indicated that voltage-activated sodium current in myoblasts was more resistant to block by tetrodotoxin (TTX) than that in myotubes. Single-channel recording from both cell types showed two classes of sodium channels. One class had a lower single-channel conductance, activated at more hyperpolarized voltages, and was more resistant to TTX than the other. The proportion of TTX-resistant to TTX-sensitive sodium channels was higher in myoblasts than in myotubes. Thus, the difference in TTX sensitivity between myoblasts and myotubes can be explained by a difference in the proportion of the two classes of sodium channels. In addition, the lower conductance of TTX-resistant channels provides insight into the relationship between the TTX binding site and the external mouth of the sodium channel. 相似文献
102.
103.
The alteration of mechanical soil properties by a single stress application exceeding all previously applied stresses is analyzed for a conventionally tilled and a conservational managed (since 1992) Stagnic Luvisol. Despite the more pronounced compactness of the plough layer under conventional management, it turned out to be less rigid compared to the “relictic” plough layer under conservation management. We assume that wheeling with a sugar beet harvester (rear wheel 140 kPa, front wheel 110 kPa, total mass 37 Mg) resulted in a break up of the plough pan. This was most obvious in the conventionally tilled soil whereas under conservation tillage, the plough pan seemed to resist the induced forces. Our results suggest that a break up of the compact plough layer and the subsequent re‐arrangement of newly formed fragments results in a smaller mechanical stability of the deformed soil. Soil structural changes within the plough pan are also indicated by the alteration of the anisotropy of cohesion and precompression stress, respectively. Altered mechanical properties induced by heavy soil loading affects the soil response to subsequent loading events, which could be shown by finite‐element simulations of stress‐strain properties. The simulations showed that a decrease in soil stiffness reduces the stress attenuation within the plough pan causing compressive and shear stresses to be transmitted into deeper soil levels, while at the same time shear strain increased. 相似文献
104.
In order to determine if soil hydraulic properties present a direction‐dependent behavior, undisturbed samples were collected at different horizons and orientations (vertical, diagonal [45°], and horizontal) in structured soils in the Weichselian moraine region in northern Germany. The water‐retention curve (WRC), the saturated hydraulic conductivity (kf), and the air permeability (ka) were measured. The air‐filled porosity (?a) was determined, and pore‐continuity indices (ka/?a, ka/?a2, N) and blocked porosities (?b) were derived from the relationship between ka and ?a. The development of soil structures with defined forms and dimensions (e.g., platy by soil compaction or prismatic up to subangular‐blocky by swelling–shrinkage processes) and the presence of biopores can induce a direction‐dependent behavior of pore functions. Although the pore volume as a scalar is isotropic, the saturated hydraulic conductivity and air permeability (as a function of air‐filled porosity) can be anisotropic. This behavior was observed in pore‐continuity indices showing that the identification of soil structure can be used as a first parameter to estimate if hydraulic properties present a direction‐dependent behavior at the scale of the soil horizon. 相似文献
105.
Pedotransfer functions based on general purpose Freundlich isotherms (GPF) were derived for Cd using different combinations of input variables or development conditions. The models match the criterion of flexibility as they were derived from data of 497 soil samples, which had strongly varying soil characteristics. The prediction efficiency of the approaches was investigated by comparison of measured and simulated sorption data for 124 independent soil samples. The parameterisation of the GPF shows that models derived from data of batch sorption experiments by multiple linear regression achieve best goodness-of-fit and statistical consistency. The use of extraction data or nonlinear regression analysis results in greater deviations from the statistical optima. The best overall performance considering parameterisation and validation was observed for the models including (a) the variables ‘proton activity’, ‘clay content’, ‘soil organic carbon’, ‘sum of dithionite-extractable Fe- and Mn-oxides’ or (b) the variables ‘proton activity’, ‘potential cation exchange capacity’, ‘sum of dithionite-extractable Fe- and Mn-oxides’. 相似文献
106.
Milton da Veiga Rainer Horn Dalvan Jos Reinert Jos Miguel Reichert 《Soil & Tillage Research》2007,92(1-2):104-113
The precompression stress value defines the transition from the reloading curve to the virgin compression line in the stress–strain curve, which can be used to quantify the highest load or the most intense predrying previously applied to the soil. Thus, in soils with well-defined structured soil horizons, each layer can be characterized by such mechanical strength. Penetration resistance measurements, on the other hand, can be used to determine total soil strength profiles in the field. The effect of long-term tillage systems on physical and mechanical properties was determined in undisturbed and remolded samples collected at 5 and 15 cm depth, 6 months after applying no-till (NT), chisel plow (CP), and conventional tillage (CT) treatments, along with the application of mineral fertilizer and poultry litter. The compressibility tests were performed under confined conditions, with normal loads varying from 10 to 400 kPa after a defined predrying to −6 or −30 kPa. Penetration resistance was determined in the field, after seeding, in three positions: seeding row (SR), untrafficked interrow (UI), and recently trafficked interrow (TI). No-till system showed greater soil resistance to deformation than tilled treatments, as determined by the higher precompression stress and lower coefficient of compressibility. When original soil structure was destroyed (remolded samples), smaller differences were found. The application of extra organic matter (poultry litter) resulted in a reduction of precompression stress in undisturbed samples. Penetration resistance profiles showed greater differences among tillage treatments in the upper layer of the untrafficked interrow, where NT system showed the higher values. Smaller differences were found in the seeding row (with lower values) and in recently trafficked interrow (with higher values), showing that even traffic with a light tractor after soil tillage reduced drastically the effect of previous tillage by loosening up the soil. On the other hand, the tool used to cut the soil and to open the furrow for seeding, incorporated in the direct seeding machine, was sufficient to realleviate surface soil compaction. 相似文献
107.
Purpose
Air supply and soil moisture have significant impact on the decay time necessary for complete decomposition of an interred body. Concerning the general structure and hydraulic as well as pneumatic conditions, in many cases, a permeable refilled soil material surrounded by the undisturbed and less permeable soil outside the grave results in water ponding, less aerated conditions, and lower redox potential values within the grave. This reduces the decomposition speed or even leads to preservation of the entire body.Materials and methods
In order to ascertain soil structural processes and hydraulic properties in an earth grave within the first year after burial, a monitoring of soil redox and matric potentials was realized in newly refilled artificial (empty) graves. We surveyed four variations: undisturbed reference soil, soil backfill in artificial grave, soil backfill in artificial grave amended with 20 kg CaO m?3, and grave base and walls strewed with CaO. In the fourth artificial grave (soil backfill only), irrigation experiments were conducted in order to simulate the effects of grave maintenance on soil water budget. Pore size distribution, air conductivity, and saturated hydraulic conductivity were measured on soil core samples from the variations. The monitoring was realized with redox sensors and tensiometers in 50- and 130-cm depth in all four variations.Results and discussion
Soil structure disruption increased soil porosity but also favored saturation of the soil in context with precipitation events. Compared with the graves without amendment, the addition of quicklime resulted in higher air capacity and air permeability, saturated hydraulic conductivity, and a better-aerated (higher redox potentials) and less water-saturated soil. Non-recurring irrigation with 2.2, 4.4, and 8.9 mm did not affect the soil moisture in the 50- and 130-cm depth. Repeated irrigation with 8.9 mm on consecutive days led to persistent water saturation in the soil, especially in the 130-cm depth.Conclusions
The disturbed soil structure in the cover layer of an earth grave is sensitive to settlement and, together with a tendency to the development of stagnic conditions, this can have negative impact on soil aeration in the grave. Addition of quicklime to the soil enhances crack development in the base and walls of the grave, stabilizes the soil fragments in the backfill, and prevents intensive settlement processes. This reduces water ponding and leads to a better aeration of the soil. Irrigation of earth graves should be reduced to a minimum.108.
109.
Fertility restoration by dominant nuclear genes is essential for hybrid breeding based on cytoplasmic male sterility (CMS) to obtain heterotic effects and high seed yields. In sunflower, only the PET1 sterility inducing cytoplasm has been used in commercial hybrid breeding until now. This particular male sterility was derived from an interspecific hybrid Helianthus petiolaris × H. annuus. For the recent work we used the segregating population RHA325(CMS) × HA342, based on the PET1 cytoplasm. Molecular markers were mapped within 1.1 cM around the restoration locus Rf1. At the distal side, the marker OP-K13_454 mapped at a distance of 0.9 cM and E32M36-155R at 0.7 cM from Rf1. At the proximal side the markers E44M70-275A, E42M76-125A and E33M61-136R were mapped at 0.1, 0.2, and 0.3 cM from the restorer locus, respectively. These markers provide an excellent basis for a map based cloning approach and for marker-assisted sunflower breeding. 相似文献
110.