Bevan C, Kinne-Saffran E, Foulkes E C, Kinne R K
Max-Planck-Institut für Systemphysiologie, Dortmund, Federal Republic of Germany.
Toxicol Appl Pharmacol. 1989 Dec;101(3):461-9. doi: 10.1016/0041-008x(89)90194-4.
Using isolated brush border membrane vesicles from the kidney of the winter flounder (Pseudopleuronectes americanus), we have studied the effect of cadmium on L-alanine transport. Pretreatment of vesicles with 0.1 mM Cd2+ resulted in inhibition of L-alanine uptake in the presence of a NaCl (but not KCl) gradient. Inhibition was due to a specific interaction with the sodium-alanine cotransport system and not a change in the driving forces for alanine transport, since Cd2+ did not affect sodium-dependent D-glucose uptake. The effect of Cd2+ on Na+-alanine cotransport showed mixed-type inhibition which is only partially reversible by EDTA. Cd2+ uptake itself was shown to be time and temperature dependent, resulting in binding to both sides of the membrane. No direct correlation was possible between inhibition of L-alanine transport and the amount of Cd2+ taken up by the membranes. Nevertheless, the striking time dependence of the effect of Cd2+ on sodium-dependent L-alanine uptake and the inability of EDTA to reverse the inhibitory action of Cd2+ suggest that Cd2+ inhibits Na+-alanine cotransport at the cytoplasmic side of the membrane.
利用从美洲拟鲽（Pseudopleuronectes americanus）肾脏中分离出的刷状缘膜囊泡，我们研究了镉对L-丙氨酸转运的影响。用0.1 mM Cd²⁺预处理囊泡会导致在存在NaCl（而非KCl）梯度的情况下L-丙氨酸摄取受到抑制。抑制是由于与钠-丙氨酸共转运系统的特异性相互作用，而非丙氨酸转运驱动力的改变，因为Cd²⁺不影响钠依赖性D-葡萄糖摄取。Cd²⁺对Na⁺-丙氨酸共转运的影响表现为混合型抑制，且仅部分可被EDTA逆转。已表明Cd²⁺摄取本身具有时间和温度依赖性，会导致其与膜的两侧结合。L-丙氨酸转运的抑制与膜摄取的Cd²⁺量之间不存在直接关联。然而，Cd²⁺对钠依赖性L-丙氨酸摄取的影响具有显著的时间依赖性，且EDTA无法逆转Cd²⁺的抑制作用，这表明Cd²⁺在膜的细胞质侧抑制Na⁺-丙氨酸共转运。
