Yu D H, Huang S C, Wank S A, Mantey S, Gardner J D, Jensen R T
Digestive Diseases Branch, National Institutes of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland 20892.
Am J Physiol. 1990 Jan;258(1 Pt 1):G86-95. doi: 10.1152/ajpgi.1990.258.1.G86.
For inhibition of binding of 125I-Bolton-Hunter-labeled cholecystokinin octapeptide (125I-BH-CCK-8) to guinea pig pancreatic acini, the potencies for agonists were CCK-8 greater than desulfated [des(SO3)] CCK-8 greater than gastrin-17-I greater than pentagastrin greater than CCK-4 and for the antagonists L 364718 greater than proglumide analogue 10 greater than CBZ-CCK-(27-32)-NH2. For all non-sulfated agonists, the curves were biphasic with 20% of the tracer bound to sites with high affinity for these agonists with the following relative potencies: gastrin-17-I greater than pentagastrin greater than des(SO3)CCK-8 much greater than CCK-4; whereas 80% was bound to low-affinity sites with the following potencies: des(SO3)CCK-8 greater than gastrin-17-I = pentagastrin much greater than CCK-4. For L 364718 and proglumide analogue 10, 80% of 125I-BH-CCK-8 was bound to sites with high affinity for these antagonists and 20% to sites with low affinity. Analysis of the dose-inhibition curve for CCK-8 demonstrated two binding sites; however, comparison with the analysis in the presence of 0.1 microM gastrin-17-I suggested three binding sites. The gastrin-17-I dose-inhibition curve was significantly better fit by a three-site model than by a two-site model. The affinities of the various agonists and antagonists for the three sites were compared with their abilities to inhibit binding of 125I-gastrin-I and either stimulate or inhibit CCK-8-stimulated amylase release. These results demonstrate that 125I-BH-CCK-8 binds to three classes of receptors, not two as reported previously. Two classes are CCK-preferring, bind 83% of 125I-BH-CCK-8 at tracer concentrations, and comprise high- and low-affinity CCK-preferring sites that can be distinguished by all agonists but have equally high affinity for L 364718 and proglumide 10. A third class binds 17% of the tracer, cannot be differentiated from high-affinity CCK-preferring receptors by CCK-8, and has low affinities for L 364718 and proglumide 10. Future studies relating binding of 125I-BH-CCK-8 to biological activity or characterization of the CCK receptor by using radiolabeled agonists should consider CCK interaction with three receptors, not two as was done in the past.
为了抑制125I-博尔顿-亨特标记的胆囊收缩素八肽（125I-BH-CCK-8）与豚鼠胰腺腺泡的结合，激动剂的效力顺序为：CCK-8＞去硫酸化[des(SO3)]CCK-8＞胃泌素-17-I＞五肽胃泌素＞CCK-4；拮抗剂的效力顺序为：L 364718＞丙谷胺类似物10＞CBZ-CCK-(27-32)-NH2。对于所有非硫酸化激动剂，曲线呈双相，20%的示踪剂与对这些激动剂具有高亲和力的位点结合，其相对效力顺序为：胃泌素-17-I＞五肽胃泌素＞des(SO3)CCK-8＞＞CCK-4；而80%与低亲和力位点结合，其效力顺序为：des(SO3)CCK-8＞胃泌素-17-I = 五肽胃泌素＞＞CCK-4。对于L 364718和丙谷胺类似物10，80%的125I-BH-CCK-8与对这些拮抗剂具有高亲和力的位点结合，20%与低亲和力位点结合。CCK-8剂量抑制曲线分析显示有两个结合位点；然而，与在0.1 microM胃泌素-17-I存在下的分析比较表明有三个结合位点。胃泌素-17-I剂量抑制曲线用三位点模型拟合比用两位点模型显著更好。将各种激动剂和拮抗剂对三个位点的亲和力与其抑制125I-胃泌素-I结合以及刺激或抑制CCK-8刺激的淀粉酶释放的能力进行了比较。这些结果表明，125I-BH-CCK-8与三类受体结合，而非如先前报道的两类。两类是CCK偏好性的，在示踪剂浓度下结合83%的125I-BH-CCK-8，包括高亲和力和低亲和力的CCK偏好性位点，所有激动剂都可区分这两个位点，但它们对L 364718和丙谷胺10具有同等高的亲和力。第三类结合17%的示踪剂，CCK-8无法将其与高亲和力CCK偏好性受体区分开，且对L 364718和丙谷胺10具有低亲和力。未来关于1
