Teitler M, Leonhardt S, Weisberg E L, Hoffman B J
Department of Pharmacology and Toxicology, Albany Medical College, New York 12208.
Mol Pharmacol. 1990 Nov;38(5):594-8.
Evidence has accumulated indicating that the radioactive hallucinogens 4-bromo-3Hphenylisopropylamine ([3H]DOB) and 4-[125I]iodo-(2,5-dimethoxy)phenylisopropylamine ([125I]DOI) label an agonist high affinity state of the 5-hydroxytryptamine2 (5HT2) receptor and [3H]ketanserin labels both agonist high and low affinity states. Recently, an alternative hypothesis has been put forward proposing that the radioactive hallucinogens are labeling a 5HT2 receptor subtype distinct from the receptor labeled by [3H]ketanserin. In order to provide definitive evidence as to which of these hypotheses is correct, the rat 5HT2 receptor gene was transfected into NIH-3T3 (mammalian fibroblast) cells and COS (green monkey kidney) cells. Neither nontransfected cell type expresses 5HT2 receptors; the transfected cells expressed high affinity binding sites for both [125I] DOI (KD = 0.8 nM and Bmax = 363 fmol/mg in NIH-3T3 cells; KD = 0.2 nM and Bmax = 26 fmol/mg in COS cells) and [3H]ketanserin (KD = 0.4 nM and Bmax = 5034 fmol/mg in NIH-3T3 cells; KD = 1.0 nM and Bmax = 432 fmol/mg in COS cells). The affinities of agonists and antagonists for the [125I]DOI-labeled receptor were significantly higher than for the [3H]ketanserin-labeled receptor. The affinities of agonists and antagonists for these binding sites were essentially identical to their affinities for the sites radiolabeled by these radioligands in mammalian brain homogenates. The [125I]DOI binding was guanyl nucleotide sensitive, indicating a coupling to a GTP-binding protein. These data indicate that the 5HT2 receptor gene product contains both the guanyl nucleotide-sensitive [125I]DOI binding site and the [3H]ketanserin binding site. Therefore, these data indicate that the 5HT2 receptor gene product can produce a high affinity binding site for the phenylisopropylamine hallucinogen agonists as well as for the 5HT2 receptor antagonists. These results strongly support the two-state hypothesis for the 5HT2 receptor and do not support the multiple 5HT2 receptor subtype hypothesis.
越来越多的证据表明，放射性致幻剂4-溴-[3H]（2,5-二甲氧基）苯基异丙胺（[3H]DOB）和4-[125I]碘-（2,5-二甲氧基）苯基异丙胺（[125I]DOI）标记5-羟色胺2（5HT2）受体的激动剂高亲和力状态，而[3H]酮色林标记激动剂的高亲和力和低亲和力状态。最近，有人提出了另一种假说，认为放射性致幻剂标记的是一种与[3H]酮色林标记的受体不同的5HT2受体亚型。为了确定这些假说中哪一个是正确的，将大鼠5HT2受体基因转染到NIH-3T3（哺乳动物成纤维细胞）和COS（绿猴肾）细胞中。两种未转染的细胞类型均不表达5HT2受体；转染后的细胞对[125I]DOI（NIH-3T3细胞中KD = 0.8 nM，Bmax = 363 fmol/mg；COS细胞中KD = 0.2 nM，Bmax = 26 fmol/mg）和[3H]酮色林（NIH-3T3细胞中KD = 0.4 nM，Bmax = 5034 fmol/mg；COS细胞中KD = 1.0 nM，Bmax = 432 fmol/mg）均表达高亲和力结合位点。激动剂和拮抗剂对[125I]DOI标记受体的亲和力明显高于对[3H]酮色林标记受体的亲和力。激动剂和拮抗剂对这些结合位点的亲和力与它们对哺乳动物脑匀浆中这些放射性配体标记位点的亲和力基本相同。[125I]DOI结合对鸟苷酸敏感，表明与一种GTP结合蛋白偶联。这些数据表明，5HT2受体基因产物同时包含鸟苷酸敏感的[125I]DOI结合位点和[3H]酮色林结合位点。因此，这些数据表明，5HT2受体基因产物能够产生对苯基异丙胺致幻剂激动剂以及5HT2受体拮抗剂的高亲和力结合位点。这些结果有力地支持了5HT2受体的双态假说，而不支持5HT2受体多亚型假说。
