Impaired β-adrenergic responsiveness accentuates dysfunctional excitation-contraction coupling in an ovine model of tachypacing-induced heart failure
Impaired β-adrenergic responsiveness accentuates dysfunctional excitation-contraction coupling in an ovine model of tachypacing-induced heart failure
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DOI：
10.1113/jphysiol.2010.203984
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发表时间：
2011-03-15
影响因子：
5.5
通讯作者：
Trafford, Andrew W.
中科院分区：
文献类型：
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作者：
Briston, Sarah J.;Caldwell, Jessica L.;Trafford, Andrew W.
非技术摘要心力衰竭是指心脏无法泵出足够的血液以满足身体的需求。心力衰竭的症状通常在运动期间首先出现。运动期间，血液中去甲肾上腺素的水平会增加并激活心脏肌肉细胞上的受体（称为β受体），从而导致心脏更有力地收缩。我们发现，在心力衰竭中，对 β 受体刺激的反应减弱，这似乎是由于 β 受体未能正确向细胞内下游靶标发出信号所致。然而，绕过β受体并直接激活细胞内的下游靶标之一（一种称为腺苷酸环化酶的酶）可以恢复衰竭心脏中肌肉细胞的功能。这些观察结果为改善心力衰竭患者心脏功能的治疗提供了许多潜在靶标。正性肌力反应性降低是心力衰竭 (HF) 的特征。这项研究确定了导致心衰中β-肾上腺素能（β-AR）反应减弱的细胞Ca2+稳态和分子机制。我们通过快速起搏在绵羊身上诱发心力衰竭；测量电压钳位心室肌细胞的细胞内 Ca2+ 浓度。在 HF 中，Ca2+ 瞬态幅度和峰值 L 型 Ca2+ 电流 (ICa-L) 降低（分别为对照的 70 +/- 11% 和 50 +/- 3.7%，P < 0.05），而肌浆网 (SR) Ca2+ 含量不变。异丙肾上腺素 (ISO) 刺激 beta-AR 会增加两种细胞类型中的 Ca2+ 瞬态振幅、ICa-L 和 SR Ca2+ 含量；然而，HF 细胞的反应明显减弱（P < 0.05）。蛋白质印迹显示 HF 中蛋白磷酸酶水平升高（PP1，对照的 158 +/- 17% 和 PP2A，对照的 188 +/- 34%，P < 0.05），并且受磷蛋白磷酸化降低（Ser16，对照的 30 +/- 10% 和 Thr17，对照的 41 +/- 15%，P < 0.05）。 β-AR 受体激酶 GRK-2 在 HF 中也增加（对照的 173 +/- 38%，P < 0.05）。在 HF 中，用毛喉素激活腺苷酸环化酶可将 Ca2+ 瞬时、SR Ca2+ 含量和 SR Ca2+ 摄取率恢复到与 ISO 中对照细胞相同的水平。总之，心力衰竭时心肌对 β-AR 激动剂的反应性降低可能是由于负责调节 SR Ca2+ 含量的关键细胞内蛋白磷酸化受损，因此在 β-AR 刺激期间收缩期 Ca2+ 瞬变未能适当增加所致。
Non-technical summaryHeart failure is where the heart is unable to pump sufficient blood in order to meet the requirements of the body. Symptoms of heart failure often first present during exercise. During exercise the blood levels of a hormone, noradrenaline, increase and activate receptors on the muscle cells of the heart known as beta-receptors causing the heart to contract more forcefully. We show that in heart failure the response to beta-receptor stimulation is reduced and this appears to be due to a failure of the beta-receptor to signal correctly to downstream targets inside the cell. However, by-passing the beta-receptor and directly activating one of the downstream targets, an enzyme known as adenylyl cyclase, inside the cell restores the function of the muscle cells in failing hearts. These observations provide a number of potential targets for therapies to improve the function of the heart in patients with heart failure.Reduced inotropic responsiveness is characteristic of heart failure (HF). This study determined the cellular Ca2+ homeostatic and molecular mechanisms causing the blunted beta-adrenergic (beta-AR) response in HF. We induced HF by tachypacing in sheep; intracellular Ca2+ concentration was measured in voltage-clamped ventricular myocytes. In HF, Ca2+ transient amplitude and peak L-type Ca2+ current (ICa-L) were reduced (to 70 +/- 11% and 50 +/- 3.7% of control, respectively, P < 0.05) whereas sarcoplasmic reticulum (SR) Ca2+ content was unchanged. beta-AR stimulation with isoprenaline (ISO) increased Ca2+ transient amplitude, ICa-L and SR Ca2+ content in both cell types; however, the response of HF cells was markedly diminished (P < 0.05). Western blotting revealed an increase in protein phosphatase levels (PP1, 158 +/- 17% and PP2A, 188 +/- 34% of control, P < 0.05) and reduced phosphorylation of phospholamban in HF (Ser16, 30 +/- 10% and Thr17, 41 +/- 15% of control, P < 0.05). The beta-AR receptor kinase GRK-2 was also increased in HF (173 +/- 38% of control, P < 0.05). In HF, activation of adenylyl cyclase with forskolin rescued the Ca2+ transient, SR Ca2+ content and SR Ca2+ uptake rate to the same levels as control cells in ISO. In conclusion, the reduced responsiveness of the myocardium to beta-AR agonists in HF probably arises as a consequence of impaired phosphorylation of key intracellular proteins responsible for regulating the SR Ca2+ content and therefore failure of the systolic Ca2+ transient to increase appropriately during beta-AR stimulation.