Cardiac action potential recording protocol

APs were recorded under current-clamp mode in normal Tyrode’s solution contained (in mM): NaCl 140, KCl 5.4, CaCl₂ 1.8, MgCl₂ 1, glucose 10, HEPES 10, adjusted to pH 7.4 with NaOH. Pipette solution contained (in mM): KCl 130, NaCl 5, MgCl₂ 1, MgATP 3, EGTA 10, and HEPES 10, adjusted to pH 7.2 with KOH. The parameters of APs include APD at 30%, 50% and 90% of repolarization (APD30, APD50, and APD90), APA, MDP, and beating frequency were analyzed^{31 (link), 38 (link)}. Cells were maintained at 35 °C by a temperature controller (Warner Instruments, Hamden, USA) during the recording of APs. The APDs were corrected by the beating frequency (APDc) with Fridericia’s formula (APDc = APD/interspike interval^1/3)^{39 (link)}.