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

相似和不同的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得到证实。在这里，我们证明了在心脏、b1AR和b2AR中表达的主要b-肾上腺素能受体（bAR）亚型的异源二聚化及其生理相关性。在缺乏天然b1AR和b2AR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二聚化，这一点可以通过它们的共免疫沉淀、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来证明。结果，肌细胞收缩对异丙肾上腺素（ISO）刺激的剂量-反应曲线左移了约1.5个数量级，细胞cAMP形成对ISO的反应也随之增强，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增敏。相反，b2ar的存在极大地抑制了共存的b2ar不依赖于配体的自发活性。因此，完整心肌细胞中b1AR和b2AR的异源二聚化产生了一种具有不同功能和药理特性的新型bar群体，从而增强了对激动剂刺激的信号传导效率，同时沉默了与配体无关的受体激活，从而优化了心脏收缩性的b-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.