I K1 Channel Agonist Zacopride Alleviates Cardiac Hypertrophy and Failure via Alterations in Calcium Dyshomeostasis and Electrical Remodeling in Rats.

Intracellular Ca2+ overload, prolongation of the action potential duration (APD), and downregulation of inward rectifier potassium (I-K1) channel are hallmarks of electrical remodeling in cardiac hypertrophy and heart failure (HF). We hypothesized that enhancement of I-K1 currents is a compensation for I-K1 deficit and a novel modulation for cardiac Ca2+ homeostasis and pathological remodeling. In adult Sprague-Dawley (SD) rats in vivo, cardiac hypertrophy was induced by isoproterenol (Iso) injection (i.p., 3 mg/kg/d) for 3, 10, and 30 days. Neonatal rat ventricular myocytes (NRVMs) were isolated from 1 to 3 days SD rat pups and treated with 1 mu mol/L Iso for 24 h in vitro. The effects of zacopride, a selective I-K1/Kir2.1 channel agonist, on cardiac remodeling/hypertrophy were observed in the settings of 15 mu g/kg in vivo and 1 mu mol/L in vitro. After exposing to Iso for 3 days and 10 days, rat hearts showed distinct concentric hypertrophy and fibrosis and enhanced pumping function (P < 0.01 or P < 0.05), then progressed to dilatation and dysfunction post 30 days. Compared with the age-matched control, cardiomyocytes exhibited higher cytosolic Ca2+ (P < 0.01 or P < 0.05) and lower SR Ca2+ content (P < 0.01 or P < 0.05) all through 3, 10, and 30 days of Iso infusion. The expressions of Kir2.1 and SERCA2 were downregulated, while p-CaMKII, p-RyR2, and cleaved caspase-3 were upregulated. Iso-induced electrophysiological abnormalities were also manifested with resting potential (RP) depolarization (P < 0.01), APD prolongation (P < 0.01) in adult cardiomyocytes, and calcium overload in cultured NRVMs (P < 0.01). Zacopride treatment effectively retarded myocardial hypertrophy and fibrosis, preserved the expression of Kir2.1 and some key players in Ca2+ homeostasis, normalized the RP (P < 0.05), and abbreviated APD (P < 0.01), thus lowered cytosolic [Ca2+](i) (P < 0.01 or P < 0.05). I-K1 channel blocker BaCl2 or chloroquine largely reversed the cardioprotection of zacopride. We conclude that cardiac electrical remodeling is concurrent with structural remodeling. By enhancing cardiac I-K1, zacopride prevents Iso-induced electrical remodeling around intracellular Ca(2+ )overload, thereby attenuates cardiac structural disorder and dysfunction. Early electrical interventions may provide protection on cardiac remodeling.