Yu Ze-Yan, Tan Ju-Chiat, McMahon Aisling C, Iismaa Siiri E, Xiao Xiao-Hui, Kesteven Scott H, Reichelt Melissa E, Mohl Marion C, Smith Nicola J, Fatkin Diane, Allen David, Head Stewart I, Graham Robert M, Feneley Michael P
Victor Chang Cardiac Research Institute, Darlinghurst, Australia; Cardiology Department, St Vincent's Hospital, Darlinghurst, Australia; Faculty of Medicine, University of New South Wales, Sydney, Australia.
Victor Chang Cardiac Research Institute, Darlinghurst, Australia.
PLoS One. 2014 Jun 11;9(6):e99024. doi: 10.1371/journal.pone.0099024. eCollection 2014.
To determine the mechanisms by which the α1A-adrenergic receptor (AR) regulates cardiac contractility.
We reported previously that transgenic mice with cardiac-restricted α1A-AR overexpression (α1A-TG) exhibit enhanced contractility but not hypertrophy, despite evidence implicating this Gαq/11-coupled receptor in hypertrophy.
Contractility, calcium (Ca(2+)) kinetics and sensitivity, and contractile proteins were examined in cardiomyocytes, isolated hearts and skinned fibers from α1A-TG mice (170-fold overexpression) and their non-TG littermates (NTL) before and after α1A-AR agonist stimulation and blockade, angiotensin II (AngII), and Rho kinase (ROCK) inhibition.
Hypercontractility without hypertrophy with α1A-AR overexpression is shown to result from increased intracellular Ca(2+) release in response to agonist, augmenting the systolic amplitude of the intracellular Ca(2+) concentration [Ca(2+)]i transient without changing resting [Ca(2+)]i. In the absence of agonist, however, α1A-AR overexpression reduced contractility despite unchanged [Ca(2+)]i. This hypocontractility is not due to heterologous desensitization: the contractile response to AngII, acting via its Gαq/11-coupled receptor, was unaltered. Rather, the hypocontractility is a pleiotropic signaling effect of the α1A-AR in the absence of agonist, inhibiting RhoA/ROCK activity, resulting in hypophosphorylation of both myosin phosphatase targeting subunit 1 (MYPT1) and cardiac myosin light chain 2 (cMLC2), reducing the Ca(2+) sensitivity of the contractile machinery: all these effects were rapidly reversed by selective α1A-AR blockade. Critically, ROCK inhibition in normal hearts of NTLs without α1A-AR overexpression caused hypophosphorylation of both MYPT1 and cMLC2, and rapidly reduced basal contractility.
We report for the first time pleiotropic α1A-AR signaling and the physiological role of RhoA/ROCK signaling in maintaining contractility in the normal heart.
确定α1A - 肾上腺素能受体（AR）调节心脏收缩力的机制。
我们之前报道过，心脏特异性α1A - AR过表达的转基因小鼠（α1A - TG）表现出收缩力增强但无肥大，尽管有证据表明这种与Gαq/11偶联的受体与肥大有关。
在α1A - AR激动剂刺激与阻断、血管紧张素II（AngII）和Rho激酶（ROCK）抑制前后，检测α1A - TG小鼠（过表达170倍）及其非转基因同窝小鼠（NTL）的心肌细胞、离体心脏和脱膜肌纤维的收缩力、钙（Ca(2+)）动力学和敏感性以及收缩蛋白。
α1A - AR过表达导致的无肥大的高收缩力被证明是由于激动剂刺激后细胞内Ca(2+)释放增加，增加了细胞内Ca(2+)浓度[Ca(2+)]i瞬变的收缩期幅度，而静息[Ca(2+)]i不变。然而，在没有激动剂的情况下，α1A - AR过表达尽管[Ca(2+)]i不变，但仍降低了收缩力。这种低收缩力并非由于异源脱敏：通过其Gαq/11偶联受体起作用的对AngII的收缩反应未改变。相反，低收缩力是α1A - AR在没有激动剂时的多效性信号效应，抑制RhoA/ROCK活性，导致肌球蛋白磷酸酶靶向亚基1（MYPT1）和心肌肌球蛋白轻链2（cMLC2）均发生低磷酸化，降低了收缩机制对Ca(2+)的敏感性：所有这些效应通过选择性α1A - AR阻断迅速逆转。至关重要的是，在没有α1A - AR过表达的NTL正常心脏中抑制ROCK导致MYPT1和cMLC2均发生低磷酸化，并迅速降低基础收缩力。
我们首次报道了α1A - AR的多效性信号以及RhoA/ROCK信号在维持正常心脏收缩力中的生理作用。
