The role and outcome of the muscarinic M₂ acetylcholine receptor (M₂R) signaling in healthy and diseased cardiomyocytes is still a matter of debate. Here, we report that the long isoform of the regulator of G protein signaling 3 (RGS3L) functions as a switch in the muscarinic signaling, most likely of the M₂R, in primary cardiomyocytes. High levels of RGS3L, as found in heart failure, redirect the G_i-mediated Rac1 activation into a G_i-mediated RhoA/ROCK activation. Functionally, this switch resulted in a reduced production of reactive oxygen species (− 50%) in cardiomyocytes and an inotropic response (+ 18%) in transduced engineered heart tissues. Importantly, we could show that an adeno-associated virus 9-mediated overexpression of RGS3L in rats in vivo, increased the contractility of ventricular strips by maximally about twofold. Mechanistically, we demonstrate that this switch is mediated by a complex formation of RGS3L with the GTPase-activating protein p190RhoGAP, which balances the activity of RhoA and Rac1 by altering its substrate preference in cardiomyocytes. Enhancement of this complex formation could open new possibilities in the regulation of the contractility of the diseased heart.

_{毒蕈碱型 M 2}乙酰胆碱受体 (M ₂ R) 信号在健康和患病心肌细胞中的作用和结果仍然存在争议。在这里，我们报告了 G 蛋白信号转导调节因子 3 (RGS3L) 的长亚型在原代心肌细胞中作为毒蕈碱信号转导的开关发挥作用，很可能是 M ₂ R。如在心力衰竭中发现的那样，高水平的 RGS3L 将 G _i介导的 Rac1 激活重定向到 G _i-介导的 RhoA/ROCK 激活。从功能上讲，这种转变导致心肌细胞中活性氧的产生减少 (− 50%)，并导致转导工程心脏组织中的正性肌力反应 (+ 18%)。重要的是，我们可以证明腺相关病毒 9 介导的 RGS3L 在大鼠体内的过度表达，最大程度地增加了约两倍的心室带收缩力。从机制上讲，我们证明这种转换是由 RGS3L 与 GTP 酶激活蛋白 p190RhoGAP 的复杂形成介导的，它通过改变心肌细胞中的底物偏好来平衡 RhoA 和 Rac1 的活性。这种复杂结构的增强可能为调节患病心脏的收缩性开辟新的可能性。