Abstract 13389: Critical Role of RhoA/ROCK Signaling in Cardiac Contractility
Rationale: We have previously shown that transgenic (TG) mice with cardiac-restricted 1A-AR overexpression (170-fold) (1A-TG) exhibit enhanced ventricular contractility but not hypertrophy. We also found a hypercontractile response to 1A-AR agonist-activation in both isolated myocytes and hearts from 1A-TG mice. However, in the absence of agonist stimulation, isolated 1A-TG myocytes and hearts exhibited reduced contractility despite unchanged [Ca2+]i.
Objective: The present study investigated the role of the 1A-AR in the regulation of cardiac contractility.
Methods and Results: Basal contractility was significantly reduced by 38% in 1A-TG Langendorff hearts (P < 0.001), as compared to hearts from non-transgenic littermates (NTL). This was associated with decreased RhoA/Rho kinase (ROCK) activity (P < 0.01) and hypophosphorylation of both myosin phosphatase targeting subunit 1 (MYPT1, P < 0.01) and cardiac myosin light chain 2 (cMLC2, P < 0.01), all of which were rapidly reversed by the selective 1A-AR antagonist, RS100329. Further, basal contractility in 1A-TG and NTL hearts was strongly correlated with RhoA activity (r2 = 0.85) and with phospho-MTPY1 (r2 = 0.72) and cMLC2 levels (r2 = 0.74). In isolated NTL, but not 1A-TG hearts, inhibition of ROCK with a selective inhibitor, Y-27632, caused a rapid reduction in basal contractility by 30% (P < 0.001) and hypophosphorylation of both MYPT1 (P < 0.001) and cMLC2 (P < 0.001), responses that phenocopied the basal hypocontractility observed in isolated 1A-TG hearts. However, Y-27632 treatment had no effect on 1A-AR agonist-mediated positive inotropy in isolated hearts from NTL or 1A-TG mice.
Conclusions: Our studies demonstrate, for the first time, that neurotransmitter-independent cardiac contractility is directly regulated by RhoA/ROCK signaling, which, in turn, sensitizes the contractile machinery to [Ca2+]i by enhancing phospho-cMLC2 levels.
- © 2013 by American Heart Association, Inc.