Lucas M L, Cannon M J
Biochim Biophys Acta. 1983 Apr 21;730(1):41-8. doi: 10.1016/0005-2736(83)90314-0.
The concentration of sodium ion at the surface of rat small intestine both in vitro and in vivo was measured with plastic polymer sodium ion sensitive electrodes. In vitro the surface sodium ion concentration [Nas+] was found to be significantly higher than bulk bathing solutions of 25 mM concentration. This value could be increased by the addition of glucose to the medium and was significantly higher in the jejunum than in the ileum. Ouabain, deoxycholic acid and dithiothreitol all reduced the [Nas+] under in vitro conditions. In vivo, very high values for [Nas+] were found in the jejunum (approx. 80 mM) when the bulk concentration was 25 mM, indicating a substantial local accumulation of sodium ion at or near the brush border. This could be reduced by omission of glucose from the buffer and further reduced when magnesium was the substituent cation rather than choline. Consequently, in vivo, an appropriately orientated sodium ion gradient persists in the face of adverse tissue to bulk solution concentration gradients and potentially explains why solute absorption occurs under these circumstances. The further reduction of the correctly aligned sodium ion gradient, as required by the gradient hypothesis, by magnesium-substituted buffers and indicates that there is no real need to postulate additionally a sodium-independent magnesium-sensitive glucose transport system in vivo.
采用塑料聚合物钠离子敏感电极测量了大鼠小肠在体外和体内表面的钠离子浓度。在体外，发现表面钠离子浓度[Nas+]显著高于浓度为25 mM的大量浴液。向培养基中添加葡萄糖可提高该值，且空肠中的该值显著高于回肠。哇巴因、脱氧胆酸和二硫苏糖醇在体外条件下均降低了[Nas+]。在体内，当大量浓度为25 mM时，空肠中[Nas+]的值非常高（约80 mM），表明钠离子在刷状缘或其附近大量局部积累。从缓冲液中去除葡萄糖可降低该值，当镁作为取代阳离子而非胆碱时，该值会进一步降低。因此，在体内，面对不利的组织与大量溶液浓度梯度，适当定向的钠离子梯度持续存在，这可能解释了在这些情况下溶质吸收为何会发生。如梯度假说所要求的，用镁取代的缓冲液进一步降低了正确排列的钠离子梯度，这表明在体内没有必要额外假设存在一种不依赖钠离子的镁敏感葡萄糖转运系统。
