Heterodimer of b1-AR and b2-AR Optimizes b-AR Modulation

相似和相异的G蛋白偶联受体亚家族成员之间的分子间相互作用已在各种实验系统中显示。在这里，我们展示了异源二聚化的主要b-肾上腺素能受体（bAR）亚型表达的心脏，b1 AR和b2 AR，及其生理相关性。在缺乏天然b1 AR和b2 AR的完整成年小鼠心肌细胞中，两种bAR亚型的共表达导致受体异源二聚化，如它们的共免疫沉淀、光学分辨率下的共定位以及对亚型选择性配体的结合亲和力显著增加所证明的。结果表明，异丙肾上腺素（ISO）对bAR激动剂刺激的心肌细胞收缩的剂量-反应曲线移动了约1.5个数量级，同时细胞cAMP形成对ISO的反应增强，表明bAR亚型的分子间相互作用导致这些受体对激动剂刺激的敏感性。相反，b1 AR的存在大大抑制了共存b2 AR的配体非依赖性自发活动。因此，b1 AR和b2 AR在完整心肌细胞中的异源二聚化产生了具有不同功能和药理学特性的新型bAR群体，导致响应激动剂刺激的信号传导效率增强，同时沉默配体非依赖性受体激活，从而优化心脏收缩力的β-肾上腺素能调节。

Intermolecular interactions between members of both similar and divergent G protein-coupled receptor subfamilies have been shown in various experimental systems. Here, we demonstrate heterodimerization of predominant b-adrenergic receptor (bAR) subtypes expressed in the heart, b1AR and b2AR, and its physiological relevance. In intact adult mouse cardiac myocytes lacking native b1AR and b2AR, co-expression of both bAR subtypes led to receptor heterodimerization, as evidenced by their co-immunoprecipitation, co-localization at optical resolution, and markedly increased binding affinity for subtype-selective ligands. As a result, the dose-response curve of myocyte contraction to bAR agonist stimulation with isoproterenol (ISO) was shifted leftward by ~1.5 orders of magnitude, and the response of cellular cAMP formation to ISO was enhanced concomitantly, indicating that intermolecular interactions of bAR subtypes resulted in sensitization of these receptors in response to agonist stimulation. In contrast, the presence of b1AR greatly suppressed ligand-independent spontaneous activity of co-existing b2ARs. Thus, heterodimerization of b1AR and b2AR in intact cardiac myocytes creates a novel population of bARs with distinct functional and pharmacological properties, resulting in enhanced signaling efficiency in response to agonist stimulation while silencing ligand-independent receptor activation, thereby optimizing b-adrenergic modulation of cardiac contractility.