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|Title:||RhoA/ROCK signaling and pleiotropic α1A-adrenergic receptor regulation of cardiac contractility.|
|Authors:||Yu, Z. Y.|
Tan, J. C.
McMahon, Aisling C.
Iismaa, S. E.
Xiao, X. H.
Kesteven, S. H.
Reichelt, M. E.
Mohl, M. C.
Smith, N. J.
Head, S. I.
Graham, R. M.
Feneley, M. P.
|Publisher:||Public Library of Science|
|Citation:||PLoS One, 2014 9(6): e99024|
|Abstract:||AIMS: To determine the mechanisms by which the α1A-adrenergic receptor (AR) regulates cardiac contractility. BACKGROUND: 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. METHODS: 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. RESULTS: 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. CONCLUSIONS: 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.|
|Rights:||© 2014 Yu et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License http://creativecommons.org/licenses/by/4.0/, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.|
|Appears in Collections:||Published Articles, Dept. of Cardiovascular Sciences|
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