Corin R E, Donner D B
J Biol Chem. 1981 Nov 25;256(22):11413-6.
Kinetic experiments (uptake versus time) were utilized to examine the effects of occupancy on insulin receptor availability in rat liver plasma membranes in vitro. The following observations were made: 1) at 4 degrees C, a 3-h exposure of membranes to 100 nM native insulin, followed by removal of unbound hormone, resulted in a subsequent decrease of 125I-insulin binding at 4 degrees C. In a similar experiment at 23 degrees C, no decrease of 125I-insulin binding was observed. 2) At 23 degrees C, 131I-insulin (5 nM) was bound to membranes in a slowly reversible manner after a 3-h association. After removal of free hormone, the 131I-insulin-treated membranes displayed similar binding of 125I-insulin (1 nM) relative to controls despite persistent high level occupancy of receptors by 131I-insulin. 3) At 23 degrees C, phospholipase pretreatment of membranes enhanced 125I-insulin uptake (approximately 40%). Phospholipase-digested membranes exposed to 100 nM native insulin for 3 h bound more 125I-insulin (approximately 40%) than did nondigested membranes preincubated without native insulin. The results allowed speculation that rat liver membranes up-regulated insulin receptors after treatment with insulin and that this was mediated by exposure of cryptic binding sites.
利用动力学实验（摄取量与时间的关系）来研究占据情况对大鼠肝细胞膜胰岛素受体体外可用性的影响。得出了以下观察结果：1）在4℃时，将细胞膜与100 nM天然胰岛素接触3小时，随后去除未结合的激素，导致4℃时125I胰岛素结合量随后下降。在23℃进行的类似实验中，未观察到125I胰岛素结合量下降。2）在23℃时，131I胰岛素（5 nM）在3小时结合后以缓慢可逆的方式与细胞膜结合。去除游离激素后，尽管131I胰岛素持续高水平占据受体，但131I胰岛素处理的细胞膜相对于对照显示出相似的125I胰岛素（1 nM）结合情况。3）在23℃时，细胞膜的磷脂酶预处理增强了125I胰岛素摄取（约40%）。用100 nM天然胰岛素处理3小时的磷脂酶消化的细胞膜比未用天然胰岛素预孵育的未消化细胞膜结合更多的125I胰岛素（约40%）。这些结果推测，胰岛素处理后大鼠肝细胞膜上调了胰岛素受体，这是由隐蔽结合位点的暴露介导的。
