Keen M, Kelly E, Nobbs P, MacDermot J
Department of Pharmacology, Medical School, University of Birmingham, U.K.
Biochem Pharmacol. 1989 Nov 1;38(21):3827-33. doi: 10.1016/0006-2952(89)90592-3.
In homogenates of NG108-15 cells, adenosine analogues activate adenylate cyclase with the following order of potency: N-ethylcarboxamidoadenosine (NECA) greater than 2-chloroadenosine greater than N6-(L-phenylisopropyl)-adenosine (PIA) = cyclohexyladenosine = 2-phenylaminoadenosine. Adenosine receptor antagonists inhibit NECA-stimulated adenylate cyclase activity with the order of potency 3-isobutyl-1-methyl-xanthine (IBMX) greater than theophylline greater than caffeine. These data suggest that these ligands act at an adenosine A2 receptor. There is an apparently homogenous population of saturable 3H-NECA binding sites in homogenates of NG108-15 cells. These sites have an affinity for 3H-NECA of approximately 1 microM, and are present at a density of approximately 10 pmol/mg protein. Unlabelled NECA, 2-chloroadenosine, IBMX and theophylline displace 3H-NECA binding, with an order of potency that suggests that the 3H-NECA binding site may represent an adenosine A2 receptor. However, PIA, cyclohexyladenosine and 2-phenylaminoadenosine produce no detectable displacement of 3H-NECA binding at concentrations that produce a maximal stimulation of adenylate cyclase activity. Pretreatment of NG108-15 cells with either NECA or PIA produces a homologous desensitization of subsequent responses to all the adenosine analogues, with no effect on subsequent responses to a prostacyclin receptor agonist or NaF. This suggests that all the adenosine analogues examined activate an adenosine A2 receptor. Therefore, the 3H-NECA site at which PIA is inactive cannot represent this receptor.
在NG108 - 15细胞匀浆中，腺苷类似物激活腺苷酸环化酶的效力顺序如下：N - 乙基羧酰胺腺苷（NECA）＞2 - 氯腺苷＞N6 - （L - 苯异丙基）腺苷（PIA）=环己基腺苷 = 2 - 苯氨基腺苷。腺苷受体拮抗剂抑制NECA刺激的腺苷酸环化酶活性的效力顺序为：3 - 异丁基 - 1 - 甲基黄嘌呤（IBMX）＞茶碱＞咖啡因。这些数据表明这些配体作用于腺苷A2受体。在NG108 - 15细胞匀浆中存在明显同质的可饱和3H - NECA结合位点群体。这些位点对3H - NECA的亲和力约为1微摩尔，且以约10皮摩尔/毫克蛋白质的密度存在。未标记的NECA、2 - 氯腺苷、IBMX和茶碱可取代3H - NECA结合，其效力顺序表明3H - NECA结合位点可能代表腺苷A2受体。然而，PIA、环己基腺苷和2 - 苯氨基腺苷在产生腺苷酸环化酶活性最大刺激的浓度下，对3H - NECA结合没有可检测到的取代作用。用NECA或PIA预处理NG108 - 15细胞会使随后对所有腺苷类似物的反应产生同源脱敏，而对随后对前列环素受体激动剂或NaF的反应没有影响。这表明所检测的所有腺苷类似物均激活腺苷A2受体。因此，PIA无活性的3H - NECA位点不能代表该受体。
