Kushmerick C, Rice S J, Baldo G J, Haspel H C, Mathias R T
Department of Physiology and Biophysics, SUNY at Stony Brook, NY 11794-8661, USA.
Exp Eye Res. 1995 Sep;61(3):351-62. doi: 10.1016/s0014-4835(05)80129-0.
We have expressed frog (Rana pipiens) lens major intrinsic protein (MIP) in Xenopus oocytes and observed its effect on ion conductance, water permeability and neutral solute transport. SDS-PAGE and immunoblotting demonstrated oocytes injected with MIP mRNA expressed the protein at high levels. Immunolocalization indicated the expressed MIP migrated to the plasma membrane. MIP had no effect on the slope of oocyte I-V relations in the range -50 to +10 mV, although the averaged I-V curve was shifted 10 mV positive to control. MIP increased oocyte water permeability by a factor of 1.9 +/- 0.2, whereas the permeability to sucrose, 2-deoxyglucose, inositol, sorbitol, reduced glutathione or urea was unchanged. Glycerol permeability was enhanced in oocytes expressing MIP. In contrast to control oocytes, 3H-glycerol radioactivity accumulation did not follow first order kinetics. Radioactivity continued to accumulate even after 19 h of uptake and went beyond equilibrium with the bath. The time course of MIP-mediated glycerol uptake was modeled assuming metabolic trapping with good results. Based on this model, MIP increased oocyte glycerol permeability by a factor of 2.7.
我们已在非洲爪蟾卵母细胞中表达了蛙（豹蛙）晶状体主要内在蛋白（MIP），并观察了其对离子电导、水通透性和中性溶质转运的影响。SDS-聚丙烯酰胺凝胶电泳和免疫印迹表明，注射了MIP mRNA的卵母细胞高水平表达了该蛋白。免疫定位显示，表达的MIP迁移到了质膜。在-50至+10 mV范围内，MIP对卵母细胞电流-电压关系的斜率没有影响，尽管平均电流-电压曲线相对于对照正向偏移了10 mV。MIP使卵母细胞的水通透性提高了1.9±0.2倍，而对蔗糖、2-脱氧葡萄糖、肌醇、山梨醇、还原型谷胱甘肽或尿素的通透性没有变化。表达MIP的卵母细胞中甘油通透性增强。与对照卵母细胞不同，3H-甘油放射性积累不遵循一级动力学。即使在摄取19小时后，放射性仍继续积累，并且超过了与浴液的平衡。假设代谢捕获对MIP介导的甘油摄取的时间进程进行建模，结果良好。基于该模型，MIP使卵母细胞的甘油通透性提高了2.7倍。
