Del Castillo J R, Robinson J W
Biochim Biophys Acta. 1985 Jan 25;812(2):402-12. doi: 10.1016/0005-2736(85)90315-3.
The transport of sodium into inside-out basolateral plasma membrane vesicles from small intestinal epithelial cells has been examined. It was found, under equilibrium conditions, that binding of 22Na represents approx. 55% of the total uptake during an equilibration period of 30 min; 45% of the total uptake correspond to passive sodium entry in the vesicle space. In addition to binding and to passive Na+ entry, two distinct mechanisms capable of accumulating sodium in the intravesicular space can be demonstrated when ATP is added to the incubation medium. One transports sodium actively in the absence of potassium, whereas the other requires the presence of potassium in the interior of the vesicles. The two mechanisms can also be differentiated by their affinities for sodium, their optimal pH and by their behaviour towards different inhibitors. Thus, the mechanism that transports sodium in the absence of potassium is refractory to ouabain, but is inhibited by ethacrynic acid and furosemide, whilst the mechanism that accumulates sodium inside the vesicles in the presence of internal potassium is strongly inhibited by ouabain, is weakly inhibited by ethacrynic acid and is insensitive of furosemide. ATP is a specific stimulator of both processes, and the requirement for magnesium is absolute in both cases.
已对小肠上皮细胞内翻的基底外侧质膜囊泡中钠的转运进行了研究。发现在平衡条件下，在30分钟的平衡期内，22Na的结合约占总摄取量的55%；总摄取量的45%对应于钠被动进入囊泡空间。除了结合和被动的Na+进入外，当向孵育培养基中添加ATP时，可以证明有两种不同的机制能够在囊泡内空间积累钠。一种在没有钾的情况下主动转运钠，而另一种则需要囊泡内部存在钾。这两种机制还可以通过它们对钠的亲和力、最佳pH值以及它们对不同抑制剂的反应来区分。因此，在没有钾的情况下转运钠的机制对哇巴因不敏感，但被依他尼酸和呋塞米抑制，而在内部有钾的情况下在囊泡内积累钠的机制则被哇巴因强烈抑制，被依他尼酸弱抑制，对呋塞米不敏感。ATP是这两个过程的特异性刺激剂，两种情况下对镁的需求都是绝对的。
