Mitchell A M, Manley S W, Payne E J, Mortimer R H
Conjoint Endocrine Laboratory, Royal Brisbane Hospital, Queensland, Australia.
J Endocrinol. 1995 Aug;146(2):233-8. doi: 10.1677/joe.0.1460233.
We have studied the uptake of 125I-thyroxine (125I-T4) in the human choriocarcinoma cell line JAR. Uptake of 125I-T4 was time-dependent, stereospecific and reversible, with a saturable component of 33% after 120 min of incubation. Kinetic analysis of the initial specific uptake rates indicated the presence of a single uptake process with a Michaelis constant of 59.4 +/- 13.9 nM (n = 12) and maximum velocity of 0.29 +/- 0.06 pmol/min per mg protein. Uptake was dependent on intracellular energy as, in the presence of 2 nM potassium cyanide, saturable uptake was reduced to 60.6 +/- 8.5% (n = 4) of control uptake. Uptake was also temperature-dependent. Saturable 125I-T4 uptake after 60 min of incubation was 26.1 +/- 3.0% at 25 degrees C (n = 6) and 27.3 +/- 5.7% at 4 degrees C of control uptake at 37 degrees C. Ouabain did not inhibit 125I-T4 uptake indicating that the uptake was independent of the Na+ gradient across the cell membrane. Although T4 uptake was stereospecific, as D-T4 failed to inhibit 125I-L-T4 uptake, it was not specific for T4, as tri-iodothyronine (T3) and reverse T3 also inhibited 125I-T4 uptake. We conclude that JAR cells have a saturable, stereospecific and reversible membrane transport mechanism for T4 which is dependent on intracellular energy, but independent of the Na+ gradient across the cell membrane.
我们研究了人绒毛膜癌细胞系JAR对125I-甲状腺素（125I-T4）的摄取。125I-T4的摄取具有时间依赖性、立体特异性和可逆性，孵育120分钟后可饱和成分占33%。对初始特异性摄取率的动力学分析表明存在单一摄取过程，米氏常数为59.4±13.9 nM（n = 12），最大速度为每毫克蛋白质0.29±0.06 pmol/分钟。摄取依赖于细胞内能量，因为在存在2 nM氰化钾的情况下，可饱和摄取降至对照摄取的60.6±8.5%（n = 4）。摄取也具有温度依赖性。孵育60分钟后，25℃时可饱和的125I-T4摄取量为对照摄取量的26.1±3.0%（n = 6），4℃时为37℃对照摄取量的27.3±5.7%。哇巴因不抑制125I-T4摄取，表明摄取与跨细胞膜的Na+梯度无关。尽管T4摄取具有立体特异性，因为D-T4不能抑制125I-L-T4摄取，但它对T4并不特异，因为三碘甲状腺原氨酸（T3）和反式T3也抑制125I-T4摄取。我们得出结论，JAR细胞具有一种可饱和、立体特异性和可逆的T4膜转运机制，该机制依赖于细胞内能量，但与跨细胞膜的Na+梯度无关。
