Shirvan M H, Pollard H B, Heldman E
Laboratory of Cell Biology and Genetics, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892.
Proc Natl Acad Sci U S A. 1991 Jun 1;88(11):4860-4. doi: 10.1073/pnas.88.11.4860.
Acetylcholine evokes release from cultured bovine chromaffin cells by a mechanism that is believed to be classically nicotinic. However, we found that the full muscarinic agonist oxotremorine-M (Oxo-M) induced a robust catecholamine (CA) secretion. By contrast, muscarine, pilocarpine, bethanechol, and McN-A-343 did not elicit any secretory response. Desensitization of the response to nicotine by Oxo-M and desensitization of the response to Oxo-M by nicotine suggest that both nicotine and Oxo-M were acting at the same receptor. Additional experiments supporting this conclusion show that nicotine-induced secretion and Oxo-M-induced secretion were similarly blocked by various muscarinic and nicotinic antagonists. Moreover, secretion induced by nicotine and Oxo-M were Ca2+ dependent, and both agonists induced 45Ca2+ uptake. Equilibrium binding studies showed that [3H]Oxo-M bound to chromaffin cell membranes with a Kd value of 3.08 x 10(-8) M and a Hill coefficient of 1.00, suggesting one binding site for this ligand. Nicotine inhibited Oxo-M binding in a noncompetitive manner, suggesting that both ligands bind at two different sites on the same receptor. We propose that the receptor on bovine chromaffin cells that is coupled to secretion represents an unusual cholinergic receptor that has both nicotinic and muscarinic features.
乙酰胆碱通过一种被认为是经典烟碱样的机制，促使培养的牛嗜铬细胞释放递质。然而，我们发现完全的毒蕈碱激动剂氧化震颤素 - M（Oxo - M）可诱导强烈的儿茶酚胺（CA）分泌。相比之下，毒蕈碱、毛果芸香碱、氨甲酰甲胆碱和 McN - A - 343 均未引发任何分泌反应。Oxo - M 对尼古丁反应的脱敏以及尼古丁对 Oxo - M 反应的脱敏表明，尼古丁和 Oxo - M 作用于同一受体。支持这一结论的其他实验表明，尼古丁诱导的分泌和 Oxo - M 诱导的分泌同样被各种毒蕈碱和烟碱拮抗剂所阻断。此外，尼古丁和 Oxo - M 诱导的分泌均依赖 Ca2 +，且两种激动剂均诱导 45Ca2 +摄取。平衡结合研究表明，[3H]Oxo - M 以 3.08×10(-8) M 的 Kd 值和 1.00 的希尔系数结合到嗜铬细胞膜上，表明该配体有一个结合位点。尼古丁以非竞争性方式抑制 Oxo - M 的结合，表明两种配体在同一受体的两个不同位点结合。我们提出，与牛嗜铬细胞分泌相关的受体代表一种具有烟碱样和毒蕈碱样特征的特殊胆碱能受体。
