Rangwala F, Drisdel R C, Rakhilin S, Ko E, Atluri P, Harkins A B, Fox A P, Salman S S, Green W N
Department of Pharmacological and Physiological Sciences, University of Chicago, Chicago, IL 60637, USA.
J Neurosci. 1997 Nov 1;17(21):8201-12. doi: 10.1523/JNEUROSCI.17-21-08201.1997.
We have characterized the alpha-bungarotoxin receptors (BgtRs) found on the cell surface of undifferentiated pheochromocytoma (PC12) cells. The PC12 cells express a homogeneous population of alpha7-containing receptors that bind alpha-Bgt with high affinity (Kd = 94 pM). The BgtRs mediate most of the response elicited by nicotine, because the BgtR-specific antagonists methyllycaconitine and alpha-Bgt block approximately 90% of the whole-cell current. The binding of nicotinic agonists to cell-surface BgtRs was highly cooperative with four different agonists showing Hill coefficients in the range of 2.3-2.4. A similar agonist binding cooperativity was observed for BgtR homomers formed from chimeric alpha7/5HT3 subunits expressed in tsA 201 cells. Two classes of agonist binding sites, in the ratio of 4:1 for PC12 cell BgtRs and 3:1 for alpha7/5HT3 BgtRs, were revealed by bromoacetylcholine alkylation of the reduced sites on both PC12 BgtRs and alpha7/5HT3 BgtRs. We conclude from this data that PC12 BgtRs and alpha7/5HT3 homomers contain at least three distinguishable agonist binding sites and thus are different from other nicotinic receptors.
我们已经对未分化的嗜铬细胞瘤（PC12）细胞表面发现的α-银环蛇毒素受体（BgtRs）进行了特性描述。PC12细胞表达了一群均一的含α7的受体，这些受体以高亲和力（Kd = 94 pM）结合α-银环蛇毒素。BgtRs介导了尼古丁引发的大部分反应，因为BgtR特异性拮抗剂甲基lycaconitine和α-银环蛇毒素阻断了约90%的全细胞电流。烟碱激动剂与细胞表面BgtRs的结合具有高度协同性，四种不同的激动剂显示出的希尔系数在2.3 - 2.4范围内。在tsA 201细胞中表达的由嵌合α7/5HT3亚基形成的BgtR同聚体也观察到了类似的激动剂结合协同性。通过对PC12 BgtRs和α7/5HT3 BgtRs上还原位点的溴乙酰胆碱烷基化反应，揭示了两类激动剂结合位点，PC12细胞BgtRs的比例为4:1，α7/5HT3 BgtRs的比例为3:1。根据这些数据我们得出结论，PC12 BgtRs和α7/5HT3同聚体至少包含三个可区分的激动剂结合位点，因此与其他烟碱受体不同。
