Segal J, Ingbar S H
Hubert H. Humphrey Center for Experimental Medicine and Cancer Research, Hebrew University, Hadassah Medical School, Jerusalem, Israel.
J Endocrinol. 1990 Jan;124(1):133-40. doi: 10.1677/joe.0.1240133.
We have shown that 3,5,3'-tri-iodothyronine (T3) produces a prompt increase in sugar transport in rat thymocytes by increasing the maximal velocity without changing the Michaelis-Menten constant of the plasma membrane sugar transport system. To elucidate further the mechanism of this effect, we have now assessed the influence of T3 on the number and affinity of sugar transporters in thymocytes, measured as the sugar (2-deoxyglucose; dGlc)-displaceable binding of cytochalasin B. Cytochalasin B inhibited in a dose-related manner the uptake of dGlc by rat thymocytes with inhibition constant values of 0.19 and 0.22 mumol/l in the presence and absence of T3 respectively. Binding of cytochalasin B by the sugar-displaceable sites was rapid and saturable, demonstrating a single class of sites having an apparent dissociation constant of 0.33 +/- 0.02 (S.D.) mumol/l and maximal binding capacity of 3.73 +/- 0.48 pmol/20 x 10(6) cells (11.2 +/- 1.4 x 10(4) sites/thymocyte). In the rat thymocyte, sugar transporters were found to be located in two major subcellular pools, the plasma membrane and microsomes, the latter being about twice the size of the former. In these subcellular compartments, as well as in the intact cell, binding of [3H]cytochalasin B by the sugar-displaceable sites constituted about 40% of total cytochalasin B binding. 3,5,3'-Tri-iodothyronine in concentrations that stimulated uptake of dGlc by thymocytes had no effect on [3H]cytochalasin B binding (total and sugar-displaceable) in the intact cell and in the plasma membrane and microsomal compartments, nor did it influence the affinity and number of sugar transporters.(ABSTRACT TRUNCATED AT 250 WORDS)
我们已经表明，3,5,3'-三碘甲状腺原氨酸（T3）可通过提高最大速度而不改变质膜糖转运系统的米氏常数，使大鼠胸腺细胞中的糖转运迅速增加。为了进一步阐明这种作用的机制，我们现在评估了T3对胸腺细胞中糖转运体数量和亲和力的影响，以细胞松弛素B的糖（2-脱氧葡萄糖；dGlc）可置换结合来衡量。细胞松弛素B以剂量相关的方式抑制大鼠胸腺细胞对dGlc的摄取，在有和没有T3的情况下，抑制常数分别为0.19和0.22μmol/L。细胞松弛素B与糖可置换位点的结合迅速且具有饱和性，表明存在一类表观解离常数为0.33±0.02（标准差）μmol/L、最大结合容量为3.73±0.48 pmol/20×10⁶个细胞（11.2±1.4×10⁴个位点/胸腺细胞）的位点。在大鼠胸腺细胞中，发现糖转运体位于两个主要的亚细胞池，即质膜和微粒体中，后者的大小约为前者的两倍。在这些亚细胞区室以及完整细胞中，糖可置换位点对[³H]细胞松弛素B的结合约占细胞松弛素B总结合量的40%。刺激胸腺细胞摄取dGlc的浓度的3,5,3'-三碘甲状腺原氨酸对完整细胞、质膜和微粒体区室中[³H]细胞松弛素B的结合（总结合和糖可置换结合）没有影响，也不影响糖转运体的亲和力和数量。（摘要截断于250字）
