Jensen R T, Charlton C G, Adachi H, Jones S W, O'Donohue T L, Gardner J D
Am J Physiol. 1983 Aug;245(2):G186-95. doi: 10.1152/ajpgi.1983.245.2.G186.
We prepared 125I-secretin and studied the kinetics, stoichiometry, and chemical specificity with which the labeled peptide binds to dispersed acini prepared from guinea pig pancreas. Iodinated secretin retained intrinsic biological activity in that it was as effective but 2.5-times less potent than native secretin in its ability to bind to pancreatic acini and to increase cellular cAMP. Scatchard analysis of binding of 125I-secretin indicated that each pancreatic acinar cell has approximately 93,000 binding sites, half of which are occupied by 11 nM iodinated secretin. Binding of 125I-secretin was rapid, reversible, saturable, specific, and temperature dependent. Binding of 125I-secretin was inhibited by secretin, vasoactive intestinal peptide, PHI, and Gila monster venom but not by glucagon, gastric inhibitory polypeptide, cholecystokinin, caerulein, gastrin, bovine pancreatic polypeptide, somatostatin, neurotensin, leucine-enkephalin, methionine-enkephalin, carbachol, bombesin, litorin, eledoisin, physalaemin, or substance P. With agonists (secretin, vasoactive intestinal peptide, PHI, or Gila monster venom), as well as antagonists (C-terminal fragments of secretin), there was a close correlation between their relative potencies for inhibiting binding of 125I-secretin and their relative potencies for increasing cAMP (agonists) or inhibiting the secretin-induced increase in cAMP (antagonists). For a given agonist, however, a 40-fold higher concentration was required for half-maximal inhibition of binding of 125I-secretin than was required to produce a half-maximal increase in cellular cAMP. Thus, maximal stimulation of cellular cAMP occurs when approximately one-third of the secretin receptors are occupied by an agonist.
我们制备了¹²⁵I - 促胰液素，并研究了标记肽与豚鼠胰腺分散腺泡结合的动力学、化学计量学和化学特异性。碘化促胰液素保留了内在生物活性，因为它在与胰腺腺泡结合以及增加细胞内cAMP的能力方面与天然促胰液素一样有效，但效力低2.5倍。对¹²⁵I - 促胰液素结合的Scatchard分析表明，每个胰腺腺泡细胞约有93,000个结合位点，其中一半被11 nM碘化促胰液素占据。¹²⁵I - 促胰液素的结合迅速、可逆、可饱和、具有特异性且依赖温度。¹²⁵I - 促胰液素的结合受到促胰液素、血管活性肠肽、PHI和吉拉毒蜥毒液的抑制，但不受胰高血糖素、胃抑制多肽、胆囊收缩素、蛙皮素、胃泌素、牛胰多肽、生长抑素、神经降压素、亮氨酸脑啡肽、甲硫氨酸脑啡肽、卡巴胆碱、蛙皮素、利托林、eledoisin、physalaemin或P物质的抑制。对于激动剂（促胰液素、血管活性肠肽、PHI或吉拉毒蜥毒液）以及拮抗剂（促胰液素的C末端片段），它们抑制¹²⁵I - 促胰液素结合的相对效力与其增加cAMP（激动剂）或抑制促胰液素诱导的cAMP增加（拮抗剂）的相对效力之间存在密切相关性。然而，对于给定的激动剂，抑制¹²⁵I - 促胰液素结合达到半数最大抑制所需的浓度比产生细胞内cAMP半数最大增加所需的浓度高40倍。因此，当约三分之一的促胰液素受体被激动剂占据时，细胞内cAMP达到最大刺激。
