Endo T, Shaikh Z A
Department of Pharmacology and Toxicology, University of Rhode Island, Kingston 02881-0809.
Toxicol Appl Pharmacol. 1993 Aug;121(2):203-9. doi: 10.1006/taap.1993.1146.
The uptake and accumulation of 1-5 microM cadmium (Cd) was studied in primary cultures of rat renal cortical epithelial cells under protein-free conditions at 4 or 37 degrees C for up to 30 min. The cells were isolated from female rats by collagenase digestion and cultured for 3-7 days. Confluency of the culture, monitored morphologically as well as by total protein content, was achieved on Day 5. Cd accumulation at 1 microM concentration demonstrated an inverse relationship to the cell density; the Cd level in Day 5 culture was only 45% of that in Day 3 culture. In subconfluent cultures (Days 3 and 4) the Cd accumulation was temperature sensitive; on Day 3 the cells accumulated one-third less Cd at 4 degrees C than at 37 degrees C. In comparison, the confluent cells (Day 5) had the same Cd accumulation regardless of the incubation temperature. In these cells, preincubation with cyanide also had no significant effect on Cd accumulation, implying a lack of energy requirement for Cd uptake. As the transport of Cd may involve processes that exist for the essential metal ions, the effect of 30 microM zinc (Zn) and copper (Cu) on the accumulation of 1 microM Cd was studied in Day 5 cultures. Coincubation with Zn caused a 16% reduction in Cd levels at 37 degrees C and even greater reduction (44% of control) at 4 degrees C. Similarly, Cu inhibited Cd accumulation by 26 and 45% at 37 and 4 degrees C, respectively, as compared to the temperature-matched controls. The Vmax for the initial Cd uptake (1 min) was 125 pmol/mg protein/min and the Km was 7 microM. Both Zn and Cu exhibited competitive inhibition kinetics and doubled the Km for Cd uptake. The Ki for Zn and Cu was 23 and 30 microM, respectively. Mercury (Hg) and lead (Pb) were also tested for their ability to affect Cd accumulation. As compared to the controls, 1 microM Hg caused an 11% reduction in Cd level at 37 degrees C. In contrast, 1 microM Pb enhanced Cd accumulation by 20%. However, neither Hg nor Pb had any significant effect on Cd accumulation at 4 degrees C. All four metals had no significant effect on the efflux of Cd from the cells. Thus, these metals affected Cd accumulation by changing its uptake rather than its efflux.(ABSTRACT TRUNCATED AT 400 WORDS)
在无蛋白条件下，于4℃或37℃对大鼠肾皮质上皮细胞原代培养物中1 - 5微摩尔镉（Cd）的摄取和积累进行了长达30分钟的研究。通过胶原酶消化从雌性大鼠分离细胞，并培养3 - 7天。在第5天通过形态学以及总蛋白含量监测达到培养物汇合。1微摩尔浓度的镉积累与细胞密度呈负相关；第5天培养物中的镉水平仅为第3天培养物中的45%。在亚汇合培养物（第3天和第4天）中，镉积累对温度敏感；在第3天，细胞在4℃积累的镉比在37℃少三分之一。相比之下，汇合细胞（第5天）无论孵育温度如何，镉积累量相同。在这些细胞中，用氰化物预孵育对镉积累也没有显著影响，这意味着镉摄取不需要能量。由于镉的转运可能涉及必需金属离子存在的过程，在第5天培养物中研究了30微摩尔锌（Zn）和铜（Cu）对1微摩尔镉积累的影响。与锌共孵育在37℃使镉水平降低16%，在4℃降低幅度更大（为对照的44%）。同样，与温度匹配的对照相比，铜在37℃和4℃分别抑制镉积累26%和45%。初始镉摄取（1分钟）的Vmax为125皮摩尔/毫克蛋白/分钟，Km为7微摩尔。锌和铜均表现出竞争性抑制动力学，并使镉摄取的Km加倍。锌和铜的Ki分别为23和30微摩尔。还测试了汞（Hg）和铅（Pb）影响镉积累的能力。与对照相比，1微摩尔汞在37℃使镉水平降低11%。相反，1微摩尔铅使镉积累增加20%。然而，汞和铅在4℃对镉积累均无显著影响。所有四种金属对细胞中镉的外流均无显著影响。因此，这些金属通过改变镉的摄取而非外流来影响镉积累。（摘要截断于400字）
