Olgemöller B, Schwaabe S, Schleicher E D, Gerbitz K D
Institut für klinische Chemie und Forschergruppe Diabetes, Städtisches Krankenhaus Schwabing, München, F.R.G.
Biochim Biophys Acta. 1990 Apr 9;1052(1):47-52. doi: 10.1016/0167-4889(90)90056-j.
To explore the significance of hyperglycaemia as a causal factor for the appearance of diabetic angiopathies we investigated aspects of myo-inositol metabolism in porcine aortic endothelial cells. myo-Inositol was shown to be a long-living metabolite. Its uptake into the cells was mediated by a high-affinity, Na(+)-dependent uptake system inhibitable by ouabain with an apparent KM of 18.6 mumols/l, which was responsible for more than 80% of total uptake at physiological myo-inositol concentrations. Inhibition of inositol uptake by D-glucose was exclusively competitive with an apparent Ki of 24 mmol/l as shown by Lineweaver-Burk- and Dixon-plot analysis. The specificity of competitive inhibition was studied. L-Glucose which is stereochemically related to myo-inositol in the same way as the D-isomer proved to be an equally potent inhibitor. The hexoses D-galactose, D-mannose and D-fructose inhibited myo-inositol uptake to a minor extent. D-allose and 3-O-methyl-D-glucose had no inhibitory effect indicating that the OH-group of the carbon atom in 3 position is essential for the interaction with the carrier. The acyclic hexitol sorbitol also did not compete. As expected, the aldose reductase blocker sorbinil did not influence the carrier since there is no polyol pathway operating in porcine aortic endothelial cells. In accordance with the results of the uptake experiments, the incorporation of exogenous myo-inositol into membrane phosphatidylinositol was reduced at elevated extracellular glucose levels. The results raise the possibility that hyperglycaemia impairs endothelial inositol supply.
为了探究高血糖作为糖尿病血管病变成因的意义，我们研究了猪主动脉内皮细胞中肌醇代谢的相关方面。结果表明，肌醇是一种长寿代谢物。其进入细胞是由一种高亲和力、依赖钠离子的摄取系统介导的，该系统可被哇巴因抑制，表观米氏常数为18.6 μmol/L，在生理肌醇浓度下，该系统负责总摄取量的80%以上。通过Lineweaver-Burk和Dixon作图分析表明，D-葡萄糖对肌醇摄取的抑制作用完全是竞争性的，表观抑制常数为24 mmol/L。研究了竞争性抑制的特异性。L-葡萄糖与肌醇的立体化学关系与D-异构体相同，结果证明它是一种同样有效的抑制剂。己糖D-半乳糖、D-甘露糖和D-果糖对肌醇摄取的抑制作用较小。D-阿洛糖和3-O-甲基-D-葡萄糖没有抑制作用，这表明3位碳原子上的羟基对于与载体的相互作用至关重要。无环己糖醇山梨醇也不参与竞争。正如预期的那样，醛糖还原酶阻滞剂索比尼尔对载体没有影响，因为在猪主动脉内皮细胞中不存在多元醇途径。根据摄取实验的结果，在细胞外葡萄糖水平升高时，外源性肌醇掺入膜磷脂酰肌醇的量减少。这些结果增加了高血糖损害内皮细胞肌醇供应的可能性。
