Kaur Jaswinder, Sharma Neeraj, Attri Savita, Gogia Lovleen, Prasad Rajendra
Department of Biochemistry, Postgraduate Institute of Medical Education and Research, Chandigarh, India.
Mol Cell Biochem. 2006 Feb;283(1-2):169-79. doi: 10.1007/s11010-006-2676-9.
We firstly characterized zinc uptake phenomenon across basolateral membrane vesicles (BLMVs) isolated from normal rat kidney. The process was found to be time, temperature, and substrate concentration dependent, and displayed saturability. Zn(2+) uptake was competitively inhibited in the presence of 2 mM Cd with Ki of 3.9 mM. Zinc uptake was also inhibited in the presence of sulfhydryl reacting compound suggesting involvement of [-]SH groups in the transport process. Further, to elucidate the effect of in vivo Cd on zinc transport in BLMVs, Cd nephrotoxicity was induced by subcutaneous administration of CdCl(2) at dose of 0.6 mg/kg/d for 5 days in a week for 12 weeks. An indolent renal failure developed in Cd exposed rats was accompanied with a significantly high urinary excretion of Cd(2+), Zn(2+) and proteins. The histopathology and electron microscopy of kidneys of Cd exposed rats documented changes of proximal tubular degeneration. Notably, Cd content in renal cortex of Cd exposed rats was 215 microg/g tissue that was higher than the critical concentration of Cd in kidneys which was associated with significantly higher Zn and metallothionein (MT) contents. Zinc uptake in BLMVs isolated from kidneys of Cd exposed rats was significantly reduced. Further, kinetic studies revealed that decrease in zinc uptake synchronized with decrease in maximal velocity (V(max)) and increase in affinity constant which is suggestive of decreased number of active zinc transporters. Furthermore, conformational modulation of Zn transporter in BLM was further supported by observed variation in transition temperature for zinc transport in BLMVs isolated from Cd-exposed kidney.
我们首先对从正常大鼠肾脏分离的基底外侧膜囊泡（BLMVs）的锌摄取现象进行了表征。发现该过程具有时间、温度和底物浓度依赖性，并表现出饱和性。在存在2 mM Cd的情况下，Zn(2+)摄取受到竞争性抑制，抑制常数Ki为3.9 mM。在存在巯基反应化合物的情况下，锌摄取也受到抑制，这表明在转运过程中涉及[-]SH基团。此外，为了阐明体内Cd对BLMVs中锌转运的影响，通过皮下注射CdCl(2)，剂量为0.6 mg/kg/d，每周5天，持续12周，诱导Cd肾毒性。Cd暴露大鼠发生了慢性肾衰竭，同时伴有Cd(2+)、Zn(2+)和蛋白质的显著高尿排泄。Cd暴露大鼠肾脏的组织病理学和电子显微镜检查记录了近端小管变性的变化。值得注意的是，Cd暴露大鼠肾皮质中的Cd含量为215μg/g组织，高于肾脏中与显著更高的Zn和金属硫蛋白（MT）含量相关的Cd临界浓度。从Cd暴露大鼠肾脏分离的BLMVs中的锌摄取显著降低。此外，动力学研究表明，锌摄取的减少与最大速度（V(max)）的降低和亲和常数的增加同步，这表明活性锌转运体的数量减少。此外，从Cd暴露肾脏分离的BLMVs中锌转运的转变温度的观察变化进一步支持了BLM中Zn转运体的构象调节。
