Chipperfield A R, Langridge-Smith J E, Steele L W
Department of Physiology, University, Dundee.
Q J Exp Physiol. 1988 May;73(3):399-411. doi: 10.1113/expphysiol.1988.sp003156.
The uptake of sodium into vesicles isolated from the microvillous, maternal-facing plasma membrane of human placenta was studied. In equilibrium exchange conditions, sodium entry increased with time towards an equilibrium value after 30-60 min. Over 90% of the uptake was into an osmotically active space and the initial rate of uptake was halved by amiloride but unaffected by loop diuretics and capnophorin inhibitors. The apparent inhibition constant (Ki) for amiloride was 3.5 x 10(-6) M and the Michaelis constant (Km) with respect to sodium of the amiloride-sensitive component was 7-11 mM. With an imposed outward H+ gradient, sodium was transiently accumulated within the vesicles. The overshoot was abolished by amiloride and shown, by experiments with FCCP (carbonyl cyanide p-trifluoromethoxyphenylhydrazone) and potassium and valonomycin, not to be dependent on any electrical potential generated by the H+ gradient. The evidence for Na+-H+ exchange at this surface and its possible functions are discussed.
对从人胎盘微绒毛面向母体的质膜分离出的囊泡中钠的摄取进行了研究。在平衡交换条件下，钠的进入在30 - 60分钟后随时间增加至平衡值。超过90%的摄取进入了一个渗透活性空间，摄取的初始速率被氨氯地平减半，但不受襻利尿剂和碳酸酐酶抑制剂的影响。氨氯地平的表观抑制常数（Ki）为3.5×10⁻⁶ M，氨氯地平敏感成分相对于钠的米氏常数（Km）为7 - 11 mM。在施加外向H⁺梯度时，钠在囊泡内短暂积累。这种超调现象被氨氯地平消除，并且通过用FCCP（羰基氰化物对三氟甲氧基苯基腙）、钾和缬氨霉素进行的实验表明，它不依赖于由H⁺梯度产生的任何电位。讨论了该表面Na⁺-H⁺交换的证据及其可能的功能。
