Beslin A, Chantoux F, Blondeau J P, Francon J
Unité de Recherches sur la Glande Thyroïde et la Régulation Hormonale (U-96), Institut National de la Santé et de la Recherche Médicale, Le Kremlin-Bicetre, France.
Endocrinology. 1995 Dec;136(12):5385-90. doi: 10.1210/endo.136.12.7588286.
The entry of T3 and T4 into rat cultured astrocytes is mediated by a sterospecific saturable transport system. This study examines the effect of inhibiting the Na(+)-H+ exchanger and intracellular acidification on the initial velocity of [125I]T3 and [125I]T4 uptake. The resting intracellular pH (pHi) was approximately 7.15 in astrocytes exposed to CO2/HCO3(-)-free medium buffered with HEPES at pH 7.40 at 22 C. Isoosmotic replacement of extracellular sodium by mannitol or choline decreased the pHi by 0.15 pH unit and reduced uptake by about 20%. Replacing sodium with lithium had no effect on uptake. Amiloride, a specific blocker of the Na(+)-H+ exchanger, reduced pHi, as described above, and inhibited T3 and T4 uptake by about 35%. Acid loading the cells with a NH4+ pulse decreased the pHi by up to 1.2 pH units and the uptake of T3 and T4 by up to 50%. The maximum velocity of uptake was decreased, whereas the Km was unchanged. An isoosmotic increase in the extracellular K+ concentration to 50 mM had no effect on T3 uptake. The initial velocity of T3 uptake by acid-loaded cells was gradually restored by increasing the extracellular Na+ concentration. These results indicate that thyroid hormone transport into rat cultured astrocytes involves a mechanism linked to the activity of the Na(+)-H+ exchanger and the H+ concentration inside the cells.
T3和T4进入大鼠培养星形胶质细胞是由一个立体特异性可饱和转运系统介导的。本研究检测了抑制Na(+)-H+交换体和细胞内酸化对[125I]T3和[125I]T4摄取初速度的影响。在22℃下，用pH 7.40的HEPES缓冲的无CO2/HCO3(-)培养基培养的星形胶质细胞，其静息细胞内pH（pHi）约为7.15。用甘露醇或胆碱等渗替代细胞外钠会使pHi降低0.15个pH单位，并使摄取减少约20%。用锂替代钠对摄取没有影响。氨氯吡咪，一种Na(+)-H+交换体的特异性阻滞剂，如上所述降低了pHi，并抑制T3和T4摄取约35%。用NH4+脉冲使细胞酸负荷可使pHi降低多达1.2个pH单位，T3和T4摄取降低多达50%。摄取的最大速度降低，而Km不变。细胞外K+浓度等渗增加至50 mM对T3摄取没有影响。通过增加细胞外Na+浓度，酸负荷细胞的T3摄取初速度逐渐恢复。这些结果表明，甲状腺激素转运到大鼠培养星形胶质细胞涉及一种与Na(+)-H+交换体活性和细胞内H+浓度相关的机制。
