Min A D, Johansen K L, Campbell C G, Wolkoff A W
Liver Research Center, Albert Einstein College of Medicine, Bronx, New York 10461.
J Clin Invest. 1991 May;87(5):1496-502. doi: 10.1172/JCI115159.
Previous studies in cultured rat hepatocytes revealed that initial uptake of sulfobromophthalein (BSP) was markedly reduced upon removal of Cl- from the medium. In the present study, unidirectional Cl- gradients were established in short-term cultured rat hepatocytes and their effect on BSP uptake was determined. These investigations revealed that BSP uptake requires external Cl- and is not stimulated by unidirectional Cl- gradients, suggesting that BSP transport is not coupled to Cl- transport. In contrast, BSP transport is stimulated by an inside-to-outside OH- gradient, consistent with OH- exchange or H+ cotransport. As the presence of Cl- is essential for but not directly coupled to BSP transport, binding of 35S-BSP to hepatocytes was determined at 4 degrees C. This revealed an approximately 10-fold higher affinity of cells for BSP in the presence as compared to the absence of Cl- (Ka = 3.2 +/- 0.8 vs. 0.42 +/- 0.09 microM-1; P less than 0.02). Affinity of BSP for albumin was Cl(-)-independent, and was approximately 10% of its affinity for cells in the presence of Cl-. These results indicate that extracellular Cl- modulates the affinity of BSP for its hepatocyte transporter.
先前在培养的大鼠肝细胞中的研究表明，当从培养基中去除氯离子（Cl⁻）后，磺溴酞钠（BSP）的初始摄取量显著降低。在本研究中，在短期培养的大鼠肝细胞中建立了单向Cl⁻梯度，并确定了其对BSP摄取的影响。这些研究表明，BSP摄取需要细胞外Cl⁻，且不受单向Cl⁻梯度的刺激，这表明BSP转运与Cl⁻转运不偶联。相反，BSP转运受到由细胞内向细胞外的OH⁻梯度的刺激，这与OH⁻交换或H⁺共转运一致。由于Cl⁻的存在对BSP转运至关重要，但并非直接偶联，因此在4℃下测定了³⁵S - BSP与肝细胞的结合。结果显示，与不存在Cl⁻相比，存在Cl⁻时细胞对BSP具有约10倍更高的亲和力（Ka = 3.2 ± 0.8对0.42 ± 0.09 μM⁻¹；P < 0.02）。BSP对白蛋白的亲和力与Cl⁻无关，并且在存在Cl⁻时约为其对细胞亲和力的10%。这些结果表明，细胞外Cl⁻调节BSP对其肝细胞转运体的亲和力。
