ラット脂肪細胞のインスリン受容体におけるScatchard plotsの直線化
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概要
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Scatchard analysis is currently used to investigate the properties (binding affinity and number) of insulin receptors. In most cases, the Scatchard plots were curvilinear with an upward concavity. This has been explained by the presence of at least two classes of binding sites with different fixed affinities or negatively cooperative interactions between receptors. In this study, we have attempted to compare the properties of insulin receptors in adipocytes of different sizes taken from one adipose tissue region of the same individual rat. Adipocytes from epididymal fat pads, isolated by collagenase treatment, were separated into two different sizes with a technique using two nylon meshes. Small adipocytes were obtained by a filtration process resulting from the floatation through 49 μ nylon mesh. Large adipocytes were obtained from residual adipocytes, which could not penetrate through 70μ nylon mesh. By this method, large adipocytes were more homogeneous in size as compared with small adipocytes. The properties of both groups of cells were investigated by insulin binding and insulin dissociation studies. As a result, insulin binding per cell increased, and the binding was 1.5 times higher in the large adipocyte than in the small with a tracer concentration of insulin. Furthermore, Scatchard plots in insulin receptors from large homogeneous adipocytes developed a tendency to linearize and were mostly accounted for by a high affinity component (Kd 1-2 × 10<SUP>-10</SUP> M/L). On the other hand, Scatchard plots in insulin receptors from small adipocytes showed a curvilinear shape. As is usually seen, negatively cooperative interactions between receptors were demonstrated in small and large adipocytes, and the magnitude of this effect was almost the same in both groups of cells. These results suggest that Scatchard plots may be linearized by entirely homogeneous adipocytes, leading to the conclusion that the curvilinear aspect of Scatchard plots should be the result of fat cell size heterogeneity in insulin-receptor interactions.
- 一般社団法人 日本内分泌学会の論文