Curran P F, Schultz S G, Chez R A, Fuisz R E
J Gen Physiol. 1967 May;50(5):1261-86. doi: 10.1085/jgp.50.5.1261.
The relation between unidirectional influxes of Na and amino acids across the mucosal border of rabbit ileum was studied under a variety of conditions. At constant Na concentration in the mucosal bathing solution, amino acid influx followed Michaelis-Menten kinetics permitting determination of maximal influx and the apparent Michaelis constant, K(t). Reduction in Na concentration, using choline as substitute cation, caused an increase in K(t) for alanine but had no effect on maximal alanine influx. The reciprocal of K(t) was a linear function of Na concentration. Similar results were obtained for valine and leucine and these amino acids competitively inhibited alanine influx both in the presence and in the absence of Na. These results lead to a model for the transport system which involves combination of Na and amino acid with a single carrier or site leading to penetration of both solutes. The model predicts that alanine should cause an increase in Na influx and the ratio of this extra Na flux to alanine flux should vary with Na concentration. The observed relation agreed closely with predicted values for Na concentrations from 5 to 140 mM. These results support the hypothesis that interactions between Na and amino acid transport depend in part on a common entry mechanism at the mucosal border of the intestine.
在多种条件下研究了钠和氨基酸跨兔回肠黏膜边界的单向流入之间的关系。在黏膜灌流液中钠浓度恒定的情况下，氨基酸流入遵循米氏动力学，从而可以测定最大流入量和表观米氏常数K(t)。用胆碱作为替代阳离子降低钠浓度，会导致丙氨酸的K(t)增加，但对丙氨酸的最大流入量没有影响。K(t)的倒数是钠浓度的线性函数。缬氨酸和亮氨酸也得到了类似的结果，并且这些氨基酸在有钠和无钠的情况下均竞争性抑制丙氨酸的流入。这些结果得出了一个转运系统模型，该模型涉及钠和氨基酸与单一载体或位点的结合，从而导致两种溶质的通透。该模型预测，丙氨酸应会导致钠流入增加，并且这种额外的钠通量与丙氨酸通量的比值应随钠浓度而变化。观察到的关系与5至140 mM钠浓度的预测值密切相符。这些结果支持了以下假说：钠和氨基酸转运之间的相互作用部分取决于肠道黏膜边界处的共同进入机制。
