Up-regulated small-conductance calcium-activated potassium currents contribute to atrial arrhythmogenesis in high-fat feeding mice

Abstract

Aims: Metabolic syndrome (MetS) is associated with arrhythmias and cardiovascular mortality. Arrhythmogenesis in MetS results from atrial structural and electrical remodelling. The small-conductance Ca2+-activated K+ (SK) currents modulate atrial repolarization and may influence atrial arrhythmogenicity. This study investigated the regulation of SK current perturbed by a high-fat diet (HFD) to mimic MetS.

Methods and results: Thirty mice were divided into two groups that were fed with normal chow (CTL) and HFD for 4 months. Electrocardiography and echocardiography were used to detect cardiac electrical and structure remodelling. Atrial action potential duration (APD) and calcium transient duration (CaTD) were measured by optical mapping of Langendorff-perfused mice hearts. Atrial fibrillation (AF) inducibility and duration were assessed by burst pacing. Whole-cell patch clamp was performed in primarily isolated atrial myocytes for SK current density. The SK current density is higher in atrial myocytes from HFD than in CTL mice (P ≤ 0.037). The RNA and protein expression of SK channels are increased in HFD mice (P ≤ 0.041 and P ≤ 0.011, respectively). Action potential duration is shortened in HFD compared with CTL (P ≤ 0.015). The shortening of the atrial APD in HFD is reversed by the application of 100 nM apamin (P ≤ 0.043). Compared with CTL, CaTD is greater in HFD atria (P ≤ 0.029). Calcium transient decay (Tau) is significantly higher in HFD than in CTL (P = 0.001). Both APD and CaTD alternans thresholds were higher in HFD (P ≤ 0.043), along with higher inducibility and longer duration of AF in HFD (P ≤ 0.023).

Conclusion: Up-regulation of apamin-sensitive SK currents plays a partial role in the atrial arrhythmogenicity of HFD mice.

Keywords: Atrial arrhythmia; Metabolic syndrome; Small-conductance Ca2+-activated K+ (SK) currents; Very-low-density lipoprotein (VLDL).

Graphical Abstract

Figure 1

The whole-cell patch clamp of primary isolated atrial myocyte of HFD mice. (A) Representative figures of a CTL and HFD mouse. (B) Representative figures of a CTL and HFD mouse heart. Dominant epicardial fats (black arrows) were observed in the HFD but not in the CTL mouse heart. (C) Typical voltage clamp tracing of primary isolated cardiomyocytes from CTL and HFD mice. The comparison of the current density–voltage relationship of the apamin-sensitive current of primary isolated atrial myocytes isolated from CTL and HFD mice. (D) Significant difference of apamin-sensitive SK currents in both groups (n = 6 in each group).

Figure 2

Gene and protein overexpression in SK families of HFD. The qPCR (n = 8 in each group) (A) and Western blot (n = 6 in each group) (B) investigation for the regulation of SK1/2/3 of control and MetS-VLDL-treated HL-1 cells. The SK1/2/3 regulation of HFD mice model in (C) Gene expression of SKs was investigated by qPCR (n = 7 in each group). (D) IF staining of atria for SK protein expression distribution (n = 7 in each group). (E) Quantitative results of IF staining for the significant interpretation.

Figure 3

The effect of HFD in regulating APD. (A) Optical mapping setting for RA recording. (B) Representative APD recording of an HFD and CTL mouse. The APD₈₀ of (C) RA of the HFD and CTL mice at the indicated PCLs (n = 10 in each group). The application of apamin in modifying APD₈₀ of (D) CTL and (E) HFD RA from short to long PCLs is shown (n = 6 in each group).

Figure 4

HFD modulates calcium dynamic. (A) Typical Ca_i tracing from a CTL and HFD mouse. The Ca_i decay (Tau) in (B) baseline and (C) post-apmin treatment (n = 5 in each group). (D) CaTD₈₀ of RA in the indicated PCLs (n = 10 in each group). The effect of apamin in regulating RA CaTD₈₀ of (E) CTL and (F) HFD mice RA is shown in various PCLs (n = 6 in each group).

Figure 5

AF induction in HFD mice. (A) LAE and P-ECG recording in a Langendorff-perfused heart. The A indicates the atrial signal, and the V indicates the ventricular signal in LAE. The QRS indicates the ventricular signal in P-ECG. (B) AF induced by burst pacing (blue arrows) at 40 ms PCL. (C) AF lasts for more than 1 s and is followed by variable ventricular conduction. Note that the fine wave with irregular QRS is indicated of AF in P-ECG. The quantitative result of (D) AF inducibility and (E) AF duration comparison of CTL and HFD mice (n = 10 in each group). (F) and (G) show the AF inducibility and duration at baseline and after apamin treatment, respectively.

Figure 6

The thresholds of APD and CaTD alternans. (A) APD alternans at 70 ms PCL in an HFD mouse but not in the CTL mouse. The black arrow indicates long APD and the arrowhead indicates short APD. The quantitative results of the APD alternation threshold of (B) baseline and (C) post-apamin in CTL and HFD mice (n = 10 in baseline and n = 6 in post-apamin). (D) Typical image of CaTD alternans occurs at 100 ms PCL in an HFD mouse but not in a CTL mouse. The black arrow indicates large Ca_i and the arrowhead indicates small Ca_i. The quantitative results of the CaTD alternans threshold of (E) baseline and (F) post-apamin in CTL and HFD mice (n = 10 in baseline and n = 6 in post-apamin).