THE MECHANISM OF ISOTONIC WATER TRANSPORT.
THE MECHANISM OF ISOTONIC WATER TRANSPORT.
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DOI：
10.1085/jgp.48.1.15
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发表时间：
1964-09
期刊：
影响因子：
--
通讯作者：
DIAMOND JM
中科院分区：
文献类型：
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作者：
DIAMOND JM
已经研究了主动溶质转运引起水以等渗比例跨上皮膜转运的机制。实验的原理是通过改变NaCl浓度或通过添加不渗透的非电解质，当浴液的渗透压在8倍范围内变化时，测量输送流体的渗透压。将兔胆囊的体外制备物悬浮在潮湿的氧气中，不使用外部浸浴溶液，并在其滴下血清表面时收集纯输送液。在所有条件下，运输的流体被发现接近NaCl溶液等渗到任何使用的沐浴溶液。这一发现意味着胆囊中的等渗水运输机制既不是双膜效应，也不是共扩散，而是局部渗透。换句话说，主动NaCl运输在细胞膜附近的某些受限空间中维持局部高浓度的溶质，并且水响应于该局部渗透梯度而跟随NaCl。已经推导出一个方程，使人们能够计算是否被动水渗透性的器官是足够高，以占主动运输溶质的完全渗透平衡。通过应用该方程，与胆囊中的主动NaCl转运相关的水转运不能通过被动条件下的水流通道，因为这些通道非常不可渗透。此外，溶质连接的水运输未能产生预期的水流通过这些被动通道的流动电位。因此，溶质连接的水运输不发生在被动通道，而是涉及细胞膜中的特殊结构，这仍然有待确定。
The mechanism by which active solute transport causes water transport in isotonic proportions across epithelial membranes has been investigated. The principle of the experiments was to measure the osmolarity of the transported fluid when the osmolarity of the bathing solution was varied over an eightfold range by varying the NaCl concentration or by adding impermeant non-electrolytes. An in vitro preparation of rabbit gall bladder was suspended in moist oxygen without an outer bathing solution, and the pure transported fluid was collected as it dripped off the serosal surface. Under all conditions the transported fluid was found to approximate an NaCl solution isotonic to whatever bathing solution used. This finding means that the mechanism of isotonic water transport in the gall bladder is neither the double membrane effect nor co-diffusion but rather local osmosis. In other words, active NaCl transport maintains a locally high concentration of solute in some restricted space in the vicinity of the cell membrane, and water follows NaCl in response to this local osmotic gradient. An equation has been derived enabling one to calculate whether the passive water permeability of an organ is high enough to account for complete osmotic equilibration of actively transported solute. By application of this equation, water transport associated with active NaCl transport in the gall bladder cannot go through the channels for water flow under passive conditions, since these channels are grossly too impermeable. Furthermore, solute-linked water transport fails to produce the streaming potentials expected for water flow through these passive channels. Hence solute-linked water transport does not occur in the passive channels but instead involves special structures in the cell membrane, which remain to be identified.