el-Barbary A, Fenstermacher J D, Haspel H C
Department of Anesthesiology, Henry Ford Health System, Detroit, Michigan 48202-3450, USA.
Biochemistry. 1996 Dec 3;35(48):15222-7. doi: 10.1021/bi962050f.
Barbiturates inhibit GLUT-1 mediated hexose transport both in vivo [Gjedde & Rasmussen (1980) J. Neurochem. 35, 1382-1387; Otsuka et al. (1991) Am. J. Physiol. 261, R265-R275] and in vitro [Honkanen et al. (1995) Biochemistry 34, 535-544]. In the present study, the mechanism by which barbiturates inhibit GLUT-1 mediated hexose transport was examined by measuring both unidirectional zero trans and equilibrium exchange fluxes of hexoses in the functionally well-characterized, GLUT-1 rich human erythrocyte system. Unidirectional influx were both inhibited (> 80%) by 10 mM pentobarbital (PB). This symmetrical inhibition of unidirectional flux by PB was virtually independent of cis sugar concentration (2-130 mM) and exhibited an IC50 of approximately 2 mM. In contrast to unidirectional sugar flux, PB inhibition of equilibrium exchange sugar flux is attenuated by increased substrate concentration (e.g., 88% inhibition at 1 mM Glc versus 40% inhibition at 130 mM Glc in the presence of 10 mM PB) and exhibits an IC50 of approximately 10 mM at 100 mM Glc. Other barbiturates were found to inhibit sugar flux in human erythrocytes in this differential manner. These findings, when viewed with kinetic models proposed for GLUT-1 mediated transport [Carruthers (1990) Physiol. Rev. 70, 1135-1176], are consistent with barbiturates being noncompetitive inhibitors of Glc translocation and preferentially inhibiting the unoccupied form of the carrier protein. We propose, therefore, that barbiturates may prevent or alter the conformational changes associated with the reorientation of the carrier protein within the membrane. Overall, these results imply that barbiturates may more strongly inhibit GLUT-1 mediated Glc flux in vivo when the trans Glc is near zero as a result of either metabolism or another transport process.
巴比妥类药物在体内[Gjedde和Rasmussen（1980年），《神经化学杂志》35卷，1382 - 1387页；大冢等人（1991年），《美国生理学杂志》261卷，R265 - R275页]和体外[洪卡宁等人（1995年），《生物化学》34卷，535 - 544页]均能抑制GLUT - 1介导的己糖转运。在本研究中，通过测量功能特性良好、富含GLUT - 1的人红细胞系统中己糖的单向零转和平衡交换通量，研究了巴比妥类药物抑制GLUT - 1介导的己糖转运的机制。10 mM戊巴比妥（PB）对单向流入均有抑制作用（> 80%）。PB对单向通量的这种对称抑制实际上与顺式糖浓度（2 - 130 mM）无关，IC50约为2 mM。与单向糖通量不同，PB对平衡交换糖通量的抑制作用会因底物浓度增加而减弱（例如，在10 mM PB存在下，1 mM葡萄糖时抑制88%，而130 mM葡萄糖时抑制40%），在100 mM葡萄糖时IC50约为10 mM。发现其他巴比妥类药物也以这种差异方式抑制人红细胞中的糖通量。当结合为GLUT - 1介导的转运所提出的动力学模型[卡拉瑟斯（1990年），《生理学评论》第70卷，1135 - 1176页]来看这些发现时，它们与巴比妥类药物作为葡萄糖转运的非竞争性抑制剂并优先抑制载体蛋白的未占据形式是一致的。因此，我们提出，巴比妥类药物可能会阻止或改变与载体蛋白在膜内重新定向相关的构象变化。总体而言，这些结果意味着，当由于代谢或其他转运过程导致反式葡萄糖接近零时，巴比妥类药物在体内可能会更强烈地抑制GLUT - 1介导的葡萄糖通量。
