Abstract 305: Pressure Overload-Induced Myocardial Hypertrophy Causes an Electrical Remodeling of CLC-3 Chloride Channels in Mouse Heart

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Backgrand: Myocardial hypertrophy causes an increase in myocyte volume and constitutive activation of a volume-sensitive outwardly-rectifying anion channel (VSORAC). The underlying molecular mechanisms and function of VSORAC in the electrical remodeling during myocardial hypertrophy and heart failure remain undefined. We tested whether cardiac CLC-3 chloride channels play a role in the hypertrophy-induced electrophysiological remodeling.

Methods and Results: The age-matched CLC-3 knockout (Clcn3-/-) mice and their wild-type (Clcn3+/+) littermates were subjected to minimally-invasive transverse aortic banding (MTAB). In 77% (44/57) left ventricular (LV) myocytes isolated from MTAB-Clcn3+/+ mice a large VSORAC current was activated under isotonic conditions. Hypotonic cell-swelling caused no changes in the VSORAC but hypertonic cell-shrinkage significantly inhibited it. This constitutively-activated VSORAC had an anion selectivity of I->Cl->Asp-, and was inhibited by tamoxifen, PKC activation and intracellular application of anti-CLC-3 antibody. In the age-matched MTAB-Clcn3-/- mice, a significantly smaller outwardly-rectifying current was present in only 38% (36/94, P<0.05 vs MTAB-Clcn3+/+) LV myocytes. This current was neither increased by hypotonic stress nor inhibited by tamoxifen, PKC or anti-CLC-3 antibody, indicating not a VSORAC or CLC-3 current. Expression of CLC-3 protein was significantly increased in the LV tissues of MTAB-Clcn3+/+ mice but not in Sham-Clcn3+/+ and MTAB-Clcn3-/- mice. Both surface and intracardiac electrophysiological recordings revealed more atrial or ventricular arrhythmias in MTAB-Clcn3-/- mice than in MTAB- and Sham-Clcn3+/+ mice.

Conclusions: Pressure-overload-induced myocardial hypertrophy causes an upregulation of CLC-3 expression and constitutive activation of CLC-3 may serve as a novel protective mechanism against the electrical remodeling during myocardial hypertrophy and heart failure.

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