1. The suitability of inulin and mannitol as markers of the diffusional space that exists between the surface of frog skin and the outer barrier to sodium transport has been compared in experiments designed to measure the rapid uptake of sodium.2. Inulin and mannitol both equilibrate finally with the same space at the outer surface of the frog skin, but the rate at which this equilibration occurs is considerably faster for mannitol.3. The dependence of the rapid uptake of sodium on the concentration of sodium in the external medium, using mannitol to correct for extracellular sodium, can be described by simple saturation kinetics with an apparent Km for sodium entry of 24 mM and a maximal rate of uptake of 1·28 μequiv/cm2. hr.4. The effect of amiloride is to inhibit sodium uptake, the degree of inhibition depending both on the concentration of sodium in the external medium and on the level of transepithelial transport normally maintained by the skin.5. Ouabain inhibits sodium uptake when the tissue has been pre-incubated in sodium containing medium. It has no effect on sodium uptake if the pre-incubation takes place in sodium free medium.6. A short-circuit current and potential difference can be elicited across frog skin in the presence of ouabain, by increasing the concentration of sodium bathing the outside surface. This potential and short-circuit current is abolished by the presence of amiloride.7. These results provide direct evidence that amiloride acts to stop entry of sodium into the transport compartment and suggest that the ouabain inhibition of sodium uptake is mediated primarily through an increase of epithelial sodium concentration.
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机译:1.在旨在测量钠快速吸收的实验中,比较了菊粉和甘露醇是否适合作为青蛙皮肤表面与钠运输外屏障之间存在的扩散空间的标志物。2。菊粉和甘露醇最终都在青蛙皮肤的外表面上以相同的空间达到平衡,但是对于甘露醇而言,这种平衡发生的速度要快得多。3。使用甘露醇校正细胞外钠,钠的快速摄取对外部培养基中钠浓度的依赖性可以通过简单的饱和动力学来描述,其中钠进入的表观Km为24 mM,最大摄取速率为。 1·28μequiv/ cm 2 sup>。 hr.4。阿米洛利的作用是抑制钠的吸收,抑制的程度取决于外部介质中钠的浓度以及通常由皮肤维持的上皮运输水平。5。当组织已在含钠的培养基中预孵育后,瓦巴因抑制了钠的吸收。如果在无钠培养基中进行预培养,则对钠的吸收没有影响。6。在哇巴因存在的情况下,通过增加沐浴在外表面的钠的浓度,可以在青蛙的皮肤上引起短路电流和电位差。阿米洛利的存在消除了这种潜在的短路电流7。这些结果提供了直接证据,表明阿米洛利起阻止钠进入运输隔室的作用,并表明哇巴因对钠吸收的抑制作用主要是通过上皮钠浓度的增加来介导的。
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