Sakamoto C, Matosaki T, Nagao M, Baba S
Nihon Naibunpi Gakkai Zasshi. 1986 Jul 20;62(7):818-26. doi: 10.1507/endocrine1927.62.7_818.
Somatostatin binding to its receptors on rat pancreatic acinar membranes was characterized with [125I-Tyr1]somatostatin. The COOH-terminal octapeptide of cholecystokinin (CCK8), when present at various concentrations in the reaction mixture for the binding study, reduced labeled somatostatin binding in a dose-dependent manner, whereas carbachol or Ca2+ ionophore did not affect the binding. By contrast, when pancreatic acini were first treated with carbachol and thereafter [125I-Tyr1]somatostatin binding to membranes prepared from these acini was examined, carbachol reduced subsequent somatostatin binding in a dose-dependent manner. Scatchard analysis of the labeled somatostatin binding revealed that carbachol pretreatment decreased the maximum binding capacity from 142 +/- 20 fmol/mg of membrane protein to 63.5 +/- 3.5 fmol/mg of membrane protein without significantly affecting the binding affinity. To test for the possibility that CCK8 also may affect labeled somatostatin binding through an intracellular process, pancreatic acini were first treated with CCK8 and then the membrane bound CCK8 was washed out. Subsequent labeled somatostatin binding to membranes from these acini was also decreased. When 1 mM EDTA was present in the pretreatment medium, the inhibitory effect of carbachol or CCK8 was partially abolished, suggesting that an intracellular process to modulate somatostatin binding is dependent on Ca2+. On the other hand, pretreatment of acini with Ca2+ ionophore almost failed to affect subsequent labeled somatostatin binding. Results therefore suggest that CCK8 can modulate labeled somatostatin binding to pancreatic acinar membranes not only acting through an intracellular process but also at membrane sites and carbachol- or CCK8-activated intracellular process to modulate somatostatin binding is dependent on Ca2+, but Ca2+ mobilization itself is not sufficient to affect subsequent somatostatin binding.
用[125I-酪氨酸1]生长抑素对生长抑素与其在大鼠胰腺腺泡细胞膜上的受体结合进行了表征。在结合研究的反应混合物中，当胆囊收缩素（CCK8）的COOH末端八肽以不同浓度存在时，可剂量依赖性地降低标记生长抑素的结合，而卡巴胆碱或Ca2+离子载体不影响结合。相反，当胰腺腺泡先用卡巴胆碱处理，然后检测[125I-酪氨酸1]生长抑素与从这些腺泡制备的膜的结合时，卡巴胆碱可剂量依赖性地降低随后的生长抑素结合。对标记生长抑素结合的Scatchard分析表明，卡巴胆碱预处理使最大结合容量从142±20 fmol/mg膜蛋白降至63.5±3.5 fmol/mg膜蛋白，而不显著影响结合亲和力。为了测试CCK8是否也可能通过细胞内过程影响标记生长抑素的结合，胰腺腺泡先用CCK8处理，然后洗去膜结合的CCK8。随后标记生长抑素与这些腺泡膜的结合也降低。当预处理培养基中存在1 mM EDTA时，卡巴胆碱或CCK8的抑制作用部分被消除，表明调节生长抑素结合的细胞内过程依赖于Ca2+。另一方面，用Ca2+离子载体预处理腺泡几乎未能影响随后标记生长抑素的结合。因此，结果表明CCK8不仅可以通过细胞内过程，而且可以在膜位点调节标记生长抑素与胰腺腺泡膜的结合，并且卡巴胆碱或CCK8激活的调节生长抑素结合的细胞内过程依赖于Ca2+，但Ca2+动员本身不足以影响随后的生长抑素结合。
