Sloan J W, Todd G D, Martin W R
Pharmacol Biochem Behav. 1984 Jun;20(6):899-909. doi: 10.1016/0091-3057(84)90015-7.
(-)-Nicotine may bind to as many as 5 sites in the rat brain P2 preparation: A very high affinity site (KD approximately 2.2 X 10(-11) M); a positive cooperativity site; a high affinity site (KD approximately 5.2 X 10(-9) M); a low affinity site (KD approximately 4.5 X 10(-5) M) and a very low affinity site. The curvilinear nature of both Scatchard plots and kinetic curves indicates the presence of multiple binding sites. Evidence for a positive cooperativity site includes: (1) The configuration of Scatchard plots (at low concentrations) of saturation as well as inhibition curves for (-)- and (+)-nicotine. (2) The Hill number of 1.37 for the binding of low concentrations of (+/-)-[3H]nicotine. (3) Selectivity among cholinergic drugs for producing positive cooperativity. (4) Markedly different specificities of drugs for the positive cooperativity site. Thus while only (+)- and (-)-nicotine interacted with the very high affinity site, acetylcholine, atropine, mecamylamine, lobeline, carbachol, (+)-nicotine and (-)-nicotine enhanced the binding of (+/-)-[3H]nicotine and cytisine, anabasine, cotinine and choline selectively inhibited binding at the high affinity site. Several lines of evidence indicate that there is stereospecificity. (+)-Nicotine was more potent than (-)-nicotine in inducing positive cooperativity whereas (-)-nicotine was 80 times more potent than (+)-nicotine in inhibiting binding at the high affinity site. Further, the specificity of the binding sites can be altered by changing the concentration of the buffer which gives additional evidence for the lability of the nicotine binding site. Although the pharmacologic significance of the different binding sites has not been determined, these data taken together indicate that (+/-)-[3H]nicotine binds with specificity to multiple sites in the rat brain P2 preparation with a complexity not addressed heretofore.
（-）-尼古丁可能与大鼠脑P2制剂中的多达5个位点结合：一个极高亲和力位点（解离常数KD约为2.2×10⁻¹¹M）；一个正协同性位点；一个高亲和力位点（KD约为5.2×10⁻⁹M）；一个低亲和力位点（KD约为4.5×10⁻⁵M）和一个极低亲和力位点。Scatchard图和动力学曲线的曲线性质表明存在多个结合位点。正协同性位点的证据包括：（1）（-）-和（+）-尼古丁的饱和Scatchard图（低浓度时）以及抑制曲线的形态。（2）低浓度（±）-[³H]尼古丁结合的希尔系数为1.37。（3）胆碱能药物产生正协同性的选择性。（4）药物对正协同性位点的特异性明显不同。因此，虽然只有（+）-和（-）-尼古丁与极高亲和力位点相互作用，但乙酰胆碱、阿托品、美加明、洛贝林、卡巴胆碱、（+）-尼古丁和（-）-尼古丁增强了（±）-[³H]尼古丁的结合，而金雀花碱、新烟草碱、可替宁和胆碱选择性地抑制高亲和力位点的结合。几条证据表明存在立体特异性。（+）-尼古丁在诱导正协同性方面比（-）-尼古丁更有效，而（-）-尼古丁在抑制高亲和力位点的结合方面比（+）-尼古丁强80倍。此外，通过改变缓冲液浓度可以改变结合位点的特异性，这为尼古丁结合位点的不稳定性提供了额外证据。虽然不同结合位点的药理学意义尚未确定，但这些数据综合起来表明，（±）-[³H]尼古丁在大鼠脑P2制剂中特异性地与多个位点结合，其复杂性在此之前尚未涉及。
