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31.
Calcium reduces the sodium permeability of luminal membrane vesicles from toad bladder. Studies using a fast-reaction apparatus 总被引:2,自引:1,他引:1 下载免费PDF全文
Regulation of the sodium permeability of the luminal membrane is the major mechanism by which the net rate of sodium transport across tight epithelia is varied. Previous evidence has suggested that the permeability of the luminal membrane might be regulated by changes in intracellular sodium or calcium activities. To test this directly, we isolated a fraction of the plasma membrane from the toad urinary bladder, which contains a fast, amiloride-sensitive sodium flux with characteristics similar to those of the native luminal membrane. Using a flow-quench apparatus to measure the initial rate of sodium efflux from these vesicles in the millisecond time range, we have demonstrated that the isotope exchange permeability of these vesicles is very sensitive to calcium. Calcium reduces the sodium permeability, and the half-maximal inhibitory concentration is 0.5 microM, well within the range of calcium activity found in cells. Also, the permeability of the luminal membrane vesicles is little affected by the ambient sodium concentration. These results, when taken together with studies on whole tissue, suggest that cell calcium may be an important regulator of transepithelial sodium transport by its effect on luminal sodium permeability. The effect of cell sodium on permeability may be mediated by calcium rather than by sodium itself. 相似文献
32.
SMAS-platysma face lift 总被引:1,自引:0,他引:1
J Q Owsley 《Plastic and reconstructive surgery》1983,71(4):573-576
Correction of laxity in the submental area and of hypertrophic neck cords has been enhanced with the SMAS-platysma face life over that which was achieved with a standard skin face lift. Evaluation of a 6-year experience with the SMAS-platysma face lift reveals that the operation can be safely performed with an acceptably low incidence of complications. The incidence of hematoma and associated complications is less than that which occurs when cervical and submental defatting is performed in conjunction with a skin face lift. 相似文献
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The susceptibility to Tedion of haploid and diploid-haploid mixtures of eggs of Tetranychus urticae Koch was examined. It was concluded for a normal susceptible strain that haploid eggs are more susceptible to Tedion than diploid eggs. This difference in tolerance between haploid and diploid eggs could not be established for a strain resistant to Tedion.Mass crosses between the susceptible and the resistant strain were made. Susceptible females, mated by resistant males, produce susceptible haploid and resistant diploid offspring. Resistant females, mated by susceptible males, gave a resistant offspring. Both sexes can also transmit resistance to Tedion. As there was a difference in tolerance between diploid offspring in the reciprocal crosses, it is assumed that either a maternal or a cytoplasmic component is also present in the genetical mechanism of Tedion-resistance.
Zusammenfassung Es wurde die Empfindlichkeit haploider und diploid-haploider Gemische von Eiern von Tetranychus urticae Koch gegenüber Tedion untersucht. Für einen normal empfindlichen Stamm wurde aus toxikologischen Daten und einer Verschiebung des Geschlechterverhältnisses erschlossen, daß haploide Eier gegenüber Tedion empfindlicher sind als diploide. Dieser Toleranzunterschied zwischen haploiden und diploiden Nachkommen konnte bei einem gegen Tedion resistenten Stamm nicht nachgewiesen werden.Es wurden Massenkreuzungen zwischen empfindlichen und resistenten Stämmen durch-geführt. Empfindliche Weibchen, mit resistenten Männchen gepaart, produzierten empfindliche haploide und resistente diploide Nachkommen. Resistente Weibchen, mit empfindlichen Männchen gepaart, ergaben eine resistente Nachkommenschaft. Beide Geschlechter können also die Resistenz gegen Tedion übertragen. Da bei den reziproken Kreuzungen ein Toleranzunterschied zwischen den diploiden Nachkommen auftritt, wird angenommen, daß in dem genetischen Mechanismus der Tedion-Resistenz auch eine mütterliche oder eine zytoplasmatische Komponente vorhanden ist.相似文献
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Human adenoviruses: tumor production in hamsters by type 12 and 18 grown from single plaques 总被引:5,自引:0,他引:5
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SYNOPSIS. Axial muscles used for oscillatory swimming are foundnot only in fish and other vertebrates but also in some protochordatesand invertebrates. Chaetognaths have unsegmented locomotor musculaturewith some unusual features, but larvacean tunicates and thetadpole larvae of ascidians show the simplest variant of thechordate segmented axial muscle arrangement for flexing a notochordalcolumn, where all muscle cells along one side are electricallycoupled. With amphioxus, the basic fish myotomal layout is established,with two main fibre types probably used for different patternsof swimming (as in fish). There are, however, several uniquefeatures, including the flattened fibre shape and the paramyosinsystem of the notochord. Agnatha have two fibre types in themyotomes, a third type perhaps being a developmental stage inthe ontogeny of fast fibres. In lampreys, the central fibresof the characteristic fibre sandwiches in the myotomes are flattened(though less so than in amphioxus); they have a dual innervationof unknown function seen also in the fast fibre system of manyGnathostome fish groups. Hagfish fast fibres are not flattenednor do they have a dual innervation. Gnathostome fish axialmuscles are strikingly uniform in design with two possible exceptions:(1) higher teleost fast fibres which, unlike those of othergroups, are multiply-innervated and (2) tonic fibres in a fewfish, which seem not to be involved in locomotion. 相似文献
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给家兔喂以1%胆固醇及10%菜油(A组)或猪油(B组)50多天后A组血胆固醇水平(824.2±265.1mg/dl)明显低于B组(1666±693.8mg/dl);A组甘油三酯水平(51.9±19.1mg/dl)亦低于B组(104±40.2mg/dl)。二组家兔的β—VLDL的脂类组成无差别,但A组β—VLDL的apoE高于B组,分别为45.2%及37.5%。高分子量apoB(apoB_h)为33.6%,低于B组β-VLDL(47.3%)。A组β-VLDL促进小鼠腹腔巨噬细胞胆固醇堆积的程度大于B组,可能与apoE含量高有关。我们认为多不饱和脂酸减轻动脉粥样硬化(As)的作用不在于改变脂蛋白构成后阻碍泡沫细胞的形成而是促进β—VLDL从体内清除。 相似文献