Carraway R E, Mitra S P
Department of Physiology, University of Massachusetts Medical Center, Worcester 01655-0127.
Peptides. 1994;15(8):1451-9. doi: 10.1016/0196-9781(94)90123-6.
Experiments were performed to relate receptor binding to biologic activity for the contractile effect of neurotensin (NT) in guinea pig ileum. The contractile response was examined on pieces of ileum under 1 g tension in a 5 ml bath of oxygenated Tyrode's at 38 degrees C. NT contracted the longitudinal muscle (ED50, approximately 0.3 nM), the 2-3 g response peaking at 1 min and fading rapidly. In the presence of atropine (1 microM), > or = 50% of the response was blocked and the residual effect gave an ED50 of approximately 1.4 nM. In the presence of atropine and CP-96,345, a substance P receptor antagonist (0.2 microM), no contraction was observed at 20 nM NT. Thus, there were two components to the response, one involving acetylcholine (ED50, 0.3 nM) and one substance P (ED50, 1.4 nM). Using membrane preparations and 125I-labeled NT, specific, high affinity receptors for NT were demonstrated in the muscle and myenteric plexus. Scatchard analyses indicated the presence of two binding sites (Kds: approximately 0.1 nM and approximately 2 nM). Sodium ion and GTP analogs inhibited binding. Binding and biologic activity were similar in regard to dependence on specific groups within NT and sensitivity to metal ions. The high potency of Hg++ was consistent with an involvement of free sulfhydryl group(s) in the binding reaction; this was supported by work with SH-directed agents. The results suggest that two receptor types or configurations may mediate the two components of the contractile effect of NT on guinea pig ileum.
进行了实验以研究神经降压素（NT）对豚鼠回肠收缩作用的受体结合与生物活性之间的关系。在38℃下，于5ml充氧台氏液的浴槽中，对处于1g张力下的回肠片段检测其收缩反应。NT可使纵行肌收缩（ED50约为0.3nM），2 - 3g的反应在1分钟时达到峰值并迅速消退。在存在阿托品（1μM）的情况下，≥50%的反应被阻断，残余效应的ED50约为1.4nM。在存在阿托品和P物质受体拮抗剂CP - 96,345（0.2μM）的情况下，在20nM NT时未观察到收缩。因此，该反应有两个成分，一个涉及乙酰胆碱（ED50为0.3nM），另一个涉及P物质（ED50为1.4nM）。使用膜制剂和125I标记的NT，在肌肉和肌间神经丛中证实了NT的特异性、高亲和力受体。Scatchard分析表明存在两个结合位点（解离常数：约0.1nM和约2nM）。钠离子和GTP类似物抑制结合。结合和生物活性在对NT内特定基团的依赖性以及对金属离子的敏感性方面相似。Hg++的高效力与游离巯基参与结合反应一致；这得到了与SH导向剂相关工作的支持。结果表明，两种受体类型或构型可能介导了NT对豚鼠回肠收缩作用的两个成分。
