Ansanay H, Sebben M, Bockaert J, Dumuis A
Centre CNRS-INSERM de Pharmacologie-Endocrinologie, Montpellier, France.
Mol Pharmacol. 1992 Nov;42(5):808-16.
Exposure of mouse colliculi neurons to selective 5-hydroxytryptamine (5-HT)4 agonists was accompanied by a rapid desensitization of the receptor-stimulated adenylyl cyclase response. Half-maximal desensitization occurred after 2 min. Only exposure of neurons to selective 5-HT4 agonists led to a potent desensitization of the 5-HT4-mediated response. Neurons exposed to other agents, like isoproterenol, vasoactive intestinal peptide, or forskolin, that increase cAMP levels did not undergo any desensitization of 5-HT4 receptors. Activation of protein kinase A with either 8-bromo-cAMP or dibutyryl-cAMP or application of inhibitors of protein kinase A-dependent phosphorylation did not change the rate of 5-HT4-induced desensitization. No shift to lower potency of 5-HT4 agonists in the concentration-response curve was observed. These results suggest that 5-HT4 receptor agonists induced homologous but not cAMP-mediated heterologous desensitization. A good correlation was found between the affinities of nine 5-HT4 agonists and their abilities to desensitize the adenylyl cyclase response. This may indicate that homologous desensitization is a function of the mean occupancy time of the receptors by agonists. When permeabilized neurons were loaded with heparin, an inhibitor of the beta-adrenergic receptor kinase (beta ARK), 5-HT4 receptor desensitization was reduced by 30-40%. Interestingly, Zn2+, an other inhibitor of beta ARK, totally prevented 5-HT4-induced desensitization. Pretreatment of neurons with concanavalin A, reported to inhibit sequestration of beta-adrenergic receptors from the cell surface, reduced the desensitization process by 70%. These data suggest that both sequestration and phosphorylation by beta ARK, or another specific agonist-dependent receptor kinase, are involved in homologous desensitization of 5-HT4 receptors coupled to adenylyl cyclase.
将小鼠丘脑中的神经元暴露于选择性5-羟色胺（5-HT）4激动剂时，受体刺激的腺苷酸环化酶反应会迅速脱敏。2分钟后出现半数最大脱敏。只有将神经元暴露于选择性5-HT4激动剂才会导致5-HT4介导的反应有效脱敏。将神经元暴露于其他可提高环磷酸腺苷（cAMP）水平的药物，如异丙肾上腺素、血管活性肠肽或福斯可林，不会使5-HT4受体发生任何脱敏。用8-溴-cAMP或二丁酰-cAMP激活蛋白激酶A或应用蛋白激酶A依赖性磷酸化抑制剂，不会改变5-HT4诱导的脱敏速率。在浓度-反应曲线中未观察到5-HT4激动剂的效力向更低水平转变。这些结果表明，5-HT4受体激动剂诱导同源脱敏，但不诱导cAMP介导的异源脱敏。发现9种5-HT4激动剂的亲和力与其使腺苷酸环化酶反应脱敏的能力之间具有良好的相关性。这可能表明同源脱敏是激动剂使受体平均占据时间的一种功能。当用肝素（一种β-肾上腺素能受体激酶（βARK）抑制剂）加载通透化的神经元时，5-HT4受体脱敏降低了30%-40%。有趣的是，βARK的另一种抑制剂Zn2+完全阻止了5-HT4诱导的脱敏。用刀豆球蛋白A预处理神经元（据报道可抑制β-肾上腺素能受体从细胞表面的隔离），使脱敏过程降低了70%。这些数据表明，βARK或另一种特定的激动剂依赖性受体激酶的隔离和磷酸化都参与了与腺苷酸环化酶偶联的5-HT4受体的同源脱敏。
