Patch clamp recordings

Patch-clamp recordings in current clamp mode were carried out in the whole-cell configuration to measure APD of hCM as described previously[30]. Briefly, transmembrane potential was recorded from isolated hCM using perforated patch with an Axopatch 200B amplifier (Axon Instruments, Foster City, CA, USA). Cells were bathed in a chamber continuously perfused with Tyrode’s solution composed of (mmol/L) NaCl 137, KCl 5.4, CaCl₂ 2.0, MgSO₄ 1.0, Glucose 10, HEPES 10, pH to 7.35 with NaOH. Patch pipettes were filled with electrode solution composed of (mmol/L) aspartic acid 120, KCl 20, NaCl 10, MgCl₂ 2, HEPES 5, and 24 μg/ml of amphotericin-B (Sigma, St. Louis, MO), pH7.3. Myocytes were paced in current clamp mode at 1 Hz. Data acquisition was performed with an Axopatch 200B patch clamp amplifier controlled by a Digidata 1200 acquisition board driven by pCLAMP 7.0 software (Axon Instruments, Foster City, CA).