Fig. 9
From: Augmentation of myocardial If dysregulates calcium homeostasis and causes adverse cardiac remodeling
HCN4 overexpression leads to increased arrhythmogenicity. a–c Representative [Ca2+]i transients measured as change in the Fluo-4 fluorescence in cardiomyocytes from wild type a, and HCN4tg/wt b, c mice (3 months of age). a Normal behavior, exhibited by cardiomyocytes isolated from wild type mice, characterized by lack of automaticity (defined as spontaneous beating rate < 0.2 Hz) and rapid decay of Ca2+ transients under field stimulation. In contrast, cardiomyocytes from HCN4tg/wt mice frequently showed spontaneous pacemaker activity, characterized by periodic firing of [Ca2+]i transients (b), or [Ca2+]i transients with abnormal prolongation of diastolic [Ca2+]i decay (defined as D90 > 2000ms) (c). Field stimulation in a, b is denoted by green arrows. d–f Recording of spontaneous action potentials (APs) in wild type (d), and HCN4tg/wt (e, f) cardiomyocytes. While most wild type cells lacked relevant automaticity (defined as spontaneous beating rate < 0.2 Hz) (d), a subset of HCN4tg/wt cells showed spontaneous pacemaker activity, with or without afterdepolarizations (ADs). ADs (denoted by dash in e, f) frequently induced spontaneous APs (denoted by arrow in f), leading to arrhythmic firing. f depicts a detail of e. g Quantitative analysis of spontaneous activity of wild type (gray), HCN4tg/wt (black) and ivabradine-treated HCN4tg/wt (magenta) cardiomyocytes indicate a greater proportion of cells with pacemaker activity (Pace) or ADs in HCN4tg/wt cardiomyocytes compared to wild type. Remarkably, spontaneous firing and ADs were diminished after treatment with ivabradine, and percentage of cells showing arrhythmic behavior was not different from wild type thereafter. Data are expressed as mean ± s.e.m. (n = 5 independent experiments [mice] per group, 12–34 cells evaluated per experiment; *P < 0.05, **P < 0.01, ***P < 0.001 compared to wild type; ANOVA followed by Tukey test). h, i Telemetry recording from a HCN4tg/wt mouse showing an episode with premature ventricular captures that occur singular and as triplet. i depicts a detail of h. Source data are provided as a Source data file
