Bruneau C, Staedel-Flaig C, Crémel G, Leray C, Beck J P, Hubert P
Biochim Biophys Acta. 1987 May 18;928(3):287-96. doi: 10.1016/0167-4889(87)90188-1.
The influence of alterations of plasma membrane physico-chemical properties on insulin binding have been characterized in an insulin-sensitive rat hepatoma cell line adapted to grow for several generations in culture medium enriched with linoleic acid (18:2) or with 25-hydroxycholesterol. The cells took up 18:2 and 25-hydroxycholesterol added to the culture medium, without exhibiting any sign of intolerance or intoxication. These compounds respectively increased and decreased membrane fluidity at 37 degrees C. The cells demonstrated extensive changes in insulin binding parameters in response to experimental modifications of their membrane lipid composition. When determined at 4 degrees C, insulin receptors were present in the control cells at 136,000 sites/cell but this fell to 111,000 (P less than 0.05) in cells enriched in 18:2, and rose to 176,000 (P less than 0.001) in hydroxysterol-grown cells. According to a two-site model, the main effect of 18:2 was a significant increase of the number of high-affinity sites with a concomitant decrease of low-affinity sites. The hydroxysterol had the opposite effects on these parameters. The high-affinity insulin binding capacity of the hepatoma cells was affected by lipid supplementation in a similar way, whether it was determined at 4 degrees C or at 37 degrees C. Assuming a negative cooperativity model, 18:2 enhanced the degree of negative cooperativity among the sites, while 25-hydroxycholesterol reduced it. The time-course of insulin-induced receptor down-regulation was accelerated in the cells enriched in polyunsaturated fatty acids, but reduced in cells exposed to 25-hydroxycholesterol. These insulin-binding alterations cannot be directly related to modifications of cellular growth rate, receptor internalization or membrane fluidity per se, and are discussed as being more likely due to membrane lipid composition than to overall cell metabolism modifications.
在一种对胰岛素敏感的大鼠肝癌细胞系中，研究了细胞膜物理化学性质的改变对胰岛素结合的影响。该细胞系已适应在富含亚油酸（18:2）或25-羟基胆固醇的培养基中培养数代。细胞摄取添加到培养基中的18:2和25-羟基胆固醇，未表现出任何不耐受或中毒迹象。这些化合物分别在37℃时增加和降低了膜流动性。细胞因其膜脂质组成的实验性改变而在胰岛素结合参数上表现出广泛变化。在4℃测定时，对照细胞中胰岛素受体为136,000个/细胞，但在富含18:2的细胞中降至111,000个（P<0.05），而在羟基固醇培养的细胞中升至176,000个（P<0.001）。根据双位点模型，18:2的主要作用是高亲和力位点数量显著增加，同时低亲和力位点数量减少。羟基固醇对这些参数有相反的影响。无论在4℃还是37℃测定，肝癌细胞的高亲和力胰岛素结合能力都以类似方式受到脂质补充的影响。假设为负协同模型，18:2增强了位点间的负协同程度，而25-羟基胆固醇则降低了该程度。在富含多不饱和脂肪酸的细胞中，胰岛素诱导的受体内化时间进程加快，但在暴露于25-羟基胆固醇的细胞中则减慢。这些胰岛素结合改变不能直接与细胞生长速率、受体内化或膜流动性本身的改变相关，讨论认为更可能是由于膜脂质组成而非整体细胞代谢改变所致。
