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Small-Conductance Calcium-Activated Potassium Channel and Recurrent Ventricular Fibrillation in Failing Rabbit Ventricles

2011; Lippincott Williams & Wilkins; Volume: 108; Issue: 8 Linguagem: Inglês

10.1161/circresaha.110.238386

1524-4571

Su‐Kiat Chua, Po‐Cheng Chang, Mitsunori Maruyama, Isik Turker, Tetsuji Shinohara, Mark J. Shen, Zhenhui Chen, Changyu Shen, Michael Rubart‐von der Lohe, John C. Lopshire, Masahiro Ogawa, James N. Weiss, Shien‐Fong Lin, Tomohiko Ai, Peng‐Sheng Chen,

Cardiovascular Effects of Exercise

Fibrillation/defibrillation episodes in failing ventricles may be followed by action potential duration (APD) shortening and recurrent spontaneous ventricular fibrillation (SVF).We hypothesized that activation of apamin-sensitive small-conductance Ca(2+)-activated K(+) (SK) channels is responsible for the postshock APD shortening in failing ventricles.A rabbit model of tachycardia-induced heart failure was used. Simultaneous optical mapping of intracellular Ca(2+) and membrane potential (V(m)) was performed in failing and nonfailing ventricles. Three failing ventricles developed SVF (SVF group); 9 did not (no-SVF group). None of the 10 nonfailing ventricles developed SVF. Increased pacing rate and duration augmented the magnitude of APD shortening. Apamin (1 μmol/L) eliminated recurrent SVF and increased postshock APD(80) in the SVF group from 126±5 to 153±4 ms (P<0.05) and from 147±2 to 162±3 ms (P<0.05) in the no-SVF group but did not change APD(80) in nonfailing group. Whole cell patch-clamp studies at 36°C showed that the apamin-sensitive K(+) current (I(KAS)) density was significantly larger in the failing than in the normal ventricular epicardial myocytes, and epicardial I(KAS) density was significantly higher than midmyocardial and endocardial myocytes. Steady-state Ca(2+) response of I(KAS) was leftward-shifted in the failing cells compared with the normal control cells, indicating increased Ca(2+) sensitivity of I(KAS) in failing ventricles. The K(d) was 232±5 nmol/L for failing myocytes and 553±78 nmol/L for normal myocytes (P=0.002).Heart failure heterogeneously increases the sensitivity of I(KAS) to intracellular Ca(2+), leading to upregulation of I(KAS), postshock APD shortening, and recurrent SVF.