Aslam N, McArdle H J
Department of Child Health, University of Dundee, Ninewells Hospital and Medical School, Scotland.
J Cell Physiol. 1992 Jun;151(3):533-8. doi: 10.1002/jcp.1041510312.
The mechanism of zinc (Zn) uptake by microvillous membrane vesicles prepared from human term placenta has been studied. The uptake was complex, with two processes being identified. In the first process, uptake was rapid, reaching equilibrium within 2 min, and was temperature dependent, with a Q10 of 1.5. Equilibrium Zn levels were sensitive to osmotic pressure, with Zn binding at infinite osmolarity being 69% iso-osmotic value. The uptake was saturable, with a Vmax of 58 +/- 2 nmol/mg protein/min and an apparent Kt of 128 +/- 13 microM. Uptake was inhibited by increasing extravesicular K+ concentration, dropping from 0.91 +/- 0.03 nmol/mg/min at 0 extravesicular K+ to 0.47 +/- 0.03 at an extravesicular K+ concentration of 150 mM ([Zn] = 1.0 microM). In the presence of both valinomycin, an electrogenic ionophore, and nigericin, an electroneutral exchanger, an outwardly directed K+ gradient stimulated Zn uptake. Similarly, preloading vesicles with Zn and imposing an inward gradient resulted in a temperature dependent efflux of Zn. The data suggest that there is a K+ dependent Zn transporter in vesicle membranes, and we suggest that the evidence is biased in favour of a Zn/K+ exchanger rather than Zn being dependent on the membrane potential.
对从人类足月胎盘制备的微绒毛膜囊泡摄取锌（Zn）的机制进行了研究。摄取过程较为复杂，可识别出两个过程。在第一个过程中，摄取迅速，在2分钟内达到平衡，且依赖于温度，Q10为1.5。平衡锌水平对渗透压敏感，在无限渗透压下的锌结合量为等渗值的69%。摄取是可饱和的，Vmax为58±2 nmol/mg蛋白/分钟，表观Kt为128±13 μM。通过增加囊泡外钾离子浓度可抑制摄取，囊泡外钾离子浓度从0时的0.91±0.03 nmol/mg/分钟降至囊泡外钾离子浓度为150 mM（[Zn]=1.0 μM）时的0.47±0.03。在存在生电离子载体缬氨霉素和电中性交换剂尼日利亚菌素的情况下，外向钾离子梯度刺激锌摄取。同样，用锌预加载囊泡并施加内向梯度会导致锌的温度依赖性外流。数据表明囊泡膜中存在钾离子依赖性锌转运体，并且我们认为证据偏向于锌/钾离子交换体而非锌依赖于膜电位。
