Becker B N, Gettys T W, Middleton J P, Olsen C L, Albers F J, Lee S L, Fanburg B L, Raymond J R
Medical Service (Nephrology), Department of Veterans Affairs Medical Center, Durham, North Carolina 27705.
Mol Pharmacol. 1992 Nov;42(5):817-25.
Bovine pulmonary artery smooth muscle (SM) cells express a novel 5-hydroxytryptamine (5-HT) (5-HT4-like) receptor coupled to cAMP accumulation. cAMP radioimmunoassay established the agonist and antagonist profiles of this receptor. 5-HT (EC50 = 91 +/- 33 nM) and 5-methoxytryptamine were equipotent at the SM cell 5-HT receptor and both were more potent than 5-carboxamidotryptamine. Other tryptamine derivatives were less potent but remained full agonists. These findings are consistent with previous reports regarding 5-HT4 and 5-HT4-like receptors in the central nervous system. The most potent antagonists were the antidepressant compounds nortriptyline (IC50 = 177 +/- 153 nM) and zimelidine (IC50 = 202 +/- 101 nM). The 5-HT3 and 5-HT4 antagonist 3-tropanyl-indole-3-carboxylate (ICS 205-930) was also a competitive antagonist at this 5-HT4-like receptor (pA2 = 6.3). Antagonist affinities differed slightly at the SM cell receptor, compared with other 5-HT4 and 5-HT4-like receptors in the central nervous system. Nonetheless, the SM cell 5-HT4-like receptor displayed the same differential antagonist potencies as reported for these other receptors (ICS 205-930 > MDL 72222 and mianserin > ketanserin). 8-Hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) was the most potent agonist for this 5-HT4-like receptor (EC50 = 6.4 +/- 3.4 nM). 8-OH-DPAT-induced cAMP accumulation could be blocked by ICS 205-930 but not by the 5-HT1A antagonist 1-(2-methoxyphenyl)-4-[4-(2-pthalimido)butyl]piperazine hydrobromide, distinguishing the SM cell 5-HT receptor from 5-HT1A receptors. The mechanism of 5-HT-stimulated cAMP production was also investigated. First, GTP augmented basal and 5-HT-stimulated cAMP accumulation. Second, antisera to the carboxyl terminus of the alpha subunit of Gs, attenuated 5-HT-mediated adenylate cyclase activation. This established that 5-HT-stimulated cAMP accumulation in SM cells required GS. These findings suggest that SM cells express a novel 5-HT4-like receptor positively coupled to adenylate cyclase. An unexpected finding was that 8-OH-DPAT is a potent partial agonist. These studies suggest that there may be heterogeneity among 5-HT4-like receptors.
牛肺动脉平滑肌（SM）细胞表达一种与环磷酸腺苷（cAMP）积累相关的新型5-羟色胺（5-HT）（5-HT4样）受体。cAMP放射免疫测定法确定了该受体的激动剂和拮抗剂特征。5-HT（半数有效浓度[EC50]=91±33纳摩尔）和5-甲氧基色胺在SM细胞5-HT受体上效力相当，且两者均比5-羧酰胺基色胺更有效。其他色胺衍生物效力较低，但仍为完全激动剂。这些发现与先前关于中枢神经系统中5-HT4和5-HT4样受体的报道一致。最有效的拮抗剂是抗抑郁化合物去甲替林（半数抑制浓度[IC50]=177±153纳摩尔）和齐美利定（IC50=202±101纳摩尔）。5-HT3和5-HT4拮抗剂3-托烷吲哚-3-羧酸酯（ICS 205-930）在该5-HT4样受体上也是竞争性拮抗剂（拮抗常数[pA2]=6.3）。与中枢神经系统中的其他5-HT4和5-HT4样受体相比，拮抗剂在SM细胞受体上的亲和力略有不同。尽管如此，SM细胞5-HT4样受体显示出与这些其他受体报道的相同的拮抗剂效价差异（ICS 205-930＞MDL 72222以及米安色林＞酮色林）。8-羟基-2-（二正丙基氨基）四氢萘（8-OH-DPAT）是该5-HT4样受体最有效的激动剂（EC50=6.4±3.4纳摩尔）。8-OH-DPAT诱导的cAMP积累可被ICS 205-930阻断，但不能被5-HT1A拮抗剂1-（2-甲氧基苯基）-4-[4-（2-邻苯二甲酰亚胺基）丁基]哌嗪氢溴酸盐阻断，这将SM细胞5-HT受体与5-HT1A受体区分开来。还研究了5-HT刺激cAMP产生的机制。首先，鸟苷三磷酸（GTP）增强基础和5-HT刺激的cAMP积累。其次，针对Gsα亚基羧基末端的抗血清减弱了5-HT介导的腺苷酸环化酶激活。这表明5-HT刺激SM细胞中cAMP积累需要Gs。这些发现表明，SM细胞表达一种与腺苷酸环化酶正相关的新型5-HT4样受体。一个意外发现是8-OH-DPAT是一种有效的部分激动剂。这些研究表明在5-HT4样受体之间可能存在异质性。
