Department of Pharmacology and Center for Heart Failure Research, Institute of Clinical Medicine, Faculty of Medicine, University of Oslo and Oslo University Hospital, Oslo, Norway.
Department of Pharmacology and Center for Heart Failure Research, Institute of Clinical Medicine, Faculty of Medicine, University of Oslo and Oslo University Hospital, Oslo, Norway.
J Mol Cell Cardiol. 2019 Jun;131:132-145. doi: 10.1016/j.yjmcc.2019.04.017. Epub 2019 Apr 19.
Although only β-adrenergic receptors (βAR) dually couple with stimulatory G protein (G) and inhibitory G protein (G), inactivation of G enhances both βAR and βAR responsiveness. We hypothesize that G restrains spontaneous adenylyl cyclase (AC) activity independent of receptor activation. Subcellular localization of the AC5/6 subtypes varies contributing to the compartmentation of βAR signaling. The primary objectives were to determine: (1) if βAR-mediated inotropic responses were dependent upon either AC5 or AC6; (2) if intrinsic G inhibition is AC subtype selective and (3) the role of phosphodiesterases (PDE) 3/4 to regulate βAR responsiveness. βAR-mediated increases in contractile force and cAMP accumulation in cardiomyocytes were measured from wild type, AC5 and AC6 knockout (KO) mice, with or without pertussis toxin (PTX) pretreatment to inactivate G and/or after selective inhibition of PDEs 3/4. Noradrenaline potency at βARs was increased in AC6 KO. PDE4 inhibition increased noradrenaline potency in wild type and AC5 KO, but not AC6 KO. PTX increased noradrenaline potency only in wild type but increased the maximal βAR response in all mouse strains. PDE3 inhibition increased noradrenaline potency only in AC5 KO that was treated prior with PTX. βAR-evoked cAMP accumulation was increased more by PDE4 inhibition than PDE3 inhibition in wild type and AC5 KO that was amplified by G inhibition. These data indicate that βAR-mediated inotropic responses are not dependent upon either AC5 or AC6 alone. Inactivation of G enhanced βAR-mediated inotropic responses despite not coupling to G, consistent with G exerting a tonic receptor independent inhibition upon AC5/6. PDE4 seems the primary regulator of βAR signaling through AC6 in wild type. AC6 KO results in a reorganization of βAR compartmentation characterized by signaling through AC5 regulated by G, PDE3 and PDE4 that maintains normal contractile function.
尽管仅β肾上腺素能受体（βAR）双重偶联刺激 G 蛋白（G）和抑制 G 蛋白（G），但 G 的失活增强了βAR 和βAR 反应性。我们假设 G 独立于受体激活抑制自发的腺苷酸环化酶（AC）活性。AC5/6 亚型的亚细胞定位不同，导致βAR 信号的区室化。主要目的是确定：（1）βAR 介导的变力反应是否依赖于 AC5 或 AC6；（2）内在 G 抑制是否是 AC 亚型选择性的，以及（3）磷酸二酯酶（PDE）3/4 的作用以调节βAR 反应性。从野生型、AC5 和 AC6 基因敲除（KO）小鼠的心肌细胞中测量βAR 介导的收缩力增加和 cAMP 积累，在或不在百日咳毒素（PTX）预处理以失活 G 和/或在选择性抑制 PDE3/4 后。在 AC6 KO 中，去甲肾上腺素在βAR 上的效力增加。PDE4 抑制增加了去甲肾上腺素在野生型和 AC5 KO 中的效力，但在 AC6 KO 中没有增加。PTX 仅在野生型中增加去甲肾上腺素的效力，但增加了所有小鼠品系的最大βAR 反应。PDE3 抑制仅在先前用 PTX 处理的 AC5 KO 中增加去甲肾上腺素的效力。与 PDE3 抑制相比，PDE4 抑制在野生型和 AC5 KO 中增加了更多的βAR 诱导的 cAMP 积累，并且在 G 抑制下被放大。这些数据表明，βAR 介导的变力反应不依赖于 AC5 或 AC6 单独。尽管不与 G 偶联，但 G 的失活增强了βAR 介导的变力反应，这与 G 对 AC5/6 产生紧张的受体独立抑制作用一致。PDE4 似乎是通过在野生型中通过 AC6 调节βAR 信号的主要调节剂。AC6 KO 导致βAR 区室化的重新组织，其特征在于通过由 G、PDE3 和 PDE4 调节的 AC5 进行信号传递，从而维持正常的收缩功能。
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