Sullivan S J, Schonbrunn A
Endocrinology. 1987 Aug;121(2):544-52. doi: 10.1210/endo-121-2-544.
Somatostatin (SRIF) is a neuropeptide which inhibits secretion from a variety of target cells including pancreatic beta-cells. In this study we have used the RINm5F rat insulinoma cell line to characterize high affinity receptors for SRIF. The binding of 0.03 nM [125I-Tyr11]SRIF to RINm5F cells reached a plateau level within 4 h at 37 C at which time 80% of the total binding could be displaced by 100 nM unlabeled SRIF. In contrast, 100 nM concentrations of eight structurally unrelated peptides did not inhibit [125I-Tyr11]SRIF binding. Scatchard analysis indicated that RINm5F cells contained a single class of noninteracting binding sites (910 +/- 190 sites per cell) with high affinity for [125I-Tyr11]SRIF [equilibrium dissociation constant (Kd) = 0.04 +/- 0.01 nM]. Competition experiments with SRIF analogs showed that the binding affinity for [I-Tyr11]SRIF (Kd = 0.03 +/- 0.02 nM) was higher than that for either SRIF (0.24 +/- 0.04 nM) or [Tyr11]SRIF (0.27 +/- 0.04 nM) and that reduced SRIF analogs bound poorly (Kd greater than 50 nM). These results demonstrate that RINm5F cells possess specific, high affinity binding sites for SRIF. Insulin release stimulated by 20 mM leucine or 15 mM glyceraldehyde was inhibited as much as 80% by maximal concentrations (100 nM) of SRIF. The IC50 for SRIF inhibition of leucine-stimulated insulin secretion was 0.43 +/- 0.15 nM, in good agreement with the apparent Kd for binding. In fact, this close correlation between binding affinity and potency to inhibit insulin release was observed for six SRIF analogs, indicating that the characterized binding sites are the receptors which mediate the biological actions of SRIF in RINm5F cells.
生长抑素（SRIF）是一种神经肽，可抑制包括胰腺β细胞在内的多种靶细胞的分泌。在本研究中，我们使用RINm5F大鼠胰岛素瘤细胞系来表征SRIF的高亲和力受体。0.03 nM [125I-酪氨酸11]SRIF与RINm5F细胞的结合在37℃下4小时内达到平台期，此时100 nM未标记的SRIF可取代80%的总结合。相比之下，100 nM浓度的八种结构不相关的肽并未抑制[125I-酪氨酸11]SRIF的结合。Scatchard分析表明，RINm5F细胞含有一类单一的非相互作用结合位点（每个细胞910±190个位点），对[125I-酪氨酸11]SRIF具有高亲和力[平衡解离常数（Kd）=0.04±0.01 nM]。用SRIF类似物进行的竞争实验表明，对[I-酪氨酸11]SRIF（Kd = 0.03±0.02 nM）的结合亲和力高于对SRIF（0.24±0.04 nM）或[酪氨酸11]SRIF（0.27±0.04 nM）的结合亲和力，并且还原的SRIF类似物结合较差（Kd大于50 nM）。这些结果表明，RINm5F细胞具有SRIF的特异性高亲和力结合位点。20 mM亮氨酸或15 mM甘油醛刺激的胰岛素释放被最大浓度（100 nM）的SRIF抑制多达80%。SRIF抑制亮氨酸刺激的胰岛素分泌的IC50为0.43±0.15 nM，与结合的表观Kd良好吻合。事实上，六种SRIF类似物均观察到结合亲和力与抑制胰岛素释放效力之间的这种密切相关性，表明所表征的结合位点是介导SRIF在RINm5F细胞中生物学作用的受体。
