Arslan G, Kull B, Fredholm B B
Department of Physiology and Pharmacology, Karolinska Institutet, Stockholm, Sweden.
Naunyn Schmiedebergs Arch Pharmacol. 1999 Jan;359(1):28-32. doi: 10.1007/pl00005319.
PC12 cells are genetically labile and so-called wild-type cells comprise multiple subclones. We have examined the A2A adenosine receptor signal transduction pathways in four such clones (denoted clones 1, 19, 21 and 27) of PC12 cells. Adenosine A2A, A2B and A1 receptor mRNAs were detected in all four clones by RT-PCR, whereas no A3 receptor mRNA was found. A2A receptors were quantitated by radioligand binding using the antagonist radioligand [3H]SCH 58261 ([3H]-5-amino-7(2-phenylethyl)-2-(2-furyl)-pyrazolo[4,3-e]-1,2,4 triazolo [1,5-c] pyrimidine). The Bmax was highest in clone 1 followed by clones 21, 19 and 27. Whereas the amount of G(i) protein appeared similar in all four clones, the amount of G(s) protein was higher in clones 21 and 27 than in the other two clones. Maximal responses to the non-selective adenosine analogue NECA (5'-N-ethylcarboxamidoadenosine) were similar to those observed with the selective adenosine A2A receptor agonist CGS 21680 (2-[p-(2-carbonylethyl) phenylethylamino]-5'-N-ethylcarboxamidoadenosine), and were approximately equal in clones I and 21, but lower in clone 19 and very low in clone 27. For both compounds EC50 was significantly higher in clone 27 than in clone 1. In both clones the response to NECA could be competitively antagonized by a selective adenosine A2A antagonist, SCH 58261. The present results show that different clones of PC 12 cells differ widely in the cAMP increase induced by adenosine analogues and that this is due to differences in the amount of adenosine A2A receptor, G protein and effector. A large difference in receptor number resulted in differences in potency of an agonist.
PC12细胞基因不稳定，所谓的野生型细胞包含多个亚克隆。我们研究了PC12细胞的四个此类克隆（分别记为克隆1、19、21和27）中的A2A腺苷受体信号转导途径。通过逆转录聚合酶链反应（RT-PCR）在所有四个克隆中均检测到腺苷A2A、A2B和A1受体的信使核糖核酸（mRNA），而未发现A3受体mRNA。使用拮抗剂放射性配体[3H] SCH 58261（[3H]-5-氨基-7（2-苯乙基）-2-（2-呋喃基）-吡唑并[4,3-e]-1,2,4-三唑并[1,5-c]嘧啶）通过放射性配体结合对A2A受体进行定量。最大结合容量（Bmax）在克隆1中最高，其次是克隆21、19和27。虽然在所有四个克隆中G(i)蛋白的量似乎相似，但克隆21和27中G(s)蛋白的量高于其他两个克隆。对非选择性腺苷类似物NECA（5'-N-乙基甲酰胺基腺苷）的最大反应与使用选择性腺苷A2A受体激动剂CGS 21680（2-[对-（2-羰基乙基）苯乙基氨基]-5'-N-乙基甲酰胺基腺苷）时观察到的反应相似，并且在克隆1和21中大致相等，但在克隆19中较低，在克隆27中非常低。对于这两种化合物，克隆27中的半数有效浓度（EC50）显著高于克隆1。在这两个克隆中，对NECA的反应均可被选择性腺苷A2A拮抗剂SCH 58261竞争性拮抗。目前的结果表明，PC12细胞的不同克隆在腺苷类似物诱导的环磷酸腺苷（cAMP）增加方面存在很大差异，这是由于腺苷A2A受体、G蛋白和效应器数量的差异所致。受体数量的巨大差异导致激动剂效力的差异。
