Moricizine prevents atrial fibrillation by late sodium current inhibition in atrial myocytes

Figure 1. Moricizine alleviated Ang II-induced cardiac structural changes compared with saline. (A) Representative M-mode images measured from the long axis in mice treated with saline, Ang II, or moricizine cotreated. (B) Representative images used to assess left atrial area in Ang II-treated mice. Scale bars on the right side of panels A and B are measures of distance in mm. Bars on the left side of panels A and B represent contrast intensity. (C) LVEF measured by echocardiography in the three groups. (D) LAD measured by echocardiography in the three groups. (E) Body weight to heart weight ratio in the three groups. Data are presented as means ± SEM; (C,D) n=9 mice; (E) n=11 in the saline group, n=17 in the Ang II group, n=16 in the Ang II + Moricizine group. * in Figure 1B: left atria of mice. Ang II, angiotensin II; LVEF, left ventricular ejection fraction; LAD, left atrial diameter; SEM, standard error of mean.

Figure 2. Moricizine alleviated Ang II-induced cardiac electrophysiological changes compared with saline. (A) Representative ECGs illustrating the induction of AF following bolus injection of Ach-CaCl2 in the three groups. Mice cotreated with moricizine (third line) showed SR (on the left part), AF rhythm (on the middle), and the spontaneous reversion back to SR (on the right part). Recordings on the right illustrate ECG patterns during AF. (B) Summary of AF susceptibility in the three groups. Numbers above the column indicate the number of mice induced into AF. (C) Summary of the duration of AF in the three groups. n=4 saline-treated mice, n=14 Ang II-treated mice, and n=6 moricizine cotreated mice. Ang II, angiotensin II; AF, atrial fibrillation; ECG, electrocardiography; Ach, acetylcholine; CaCl2, calcium chloride; SR, sinus rhythm.

Figure 3. Moricizine reduced Ang II-induced INaL enhancement in both the left and right atria without altering the expression of Nav1.5. (A) Representative recordings of INaL from the left atria myocytes in mice treated with saline, Ang II, or those cotreated with moricizine; Cm =50 pF in each group. (B) The current density of INaL from the left atrial myocytes in the three groups. (C) Representative recordings of INaL from right atrial myocytes in the three groups; Cm=30 pF in each group. (D) The current density of INaL from the right atrial myocytes in the three groups. (E,F) Western blot analysis of the expression of Nav1.5 in the left atria of mice in the three groups. (G,H) Western blot analysis of the expression of Nav1.5 in the right atria of mice in the three groups. Data are presented as means ± SEM. (B,D) n=8 in each group. Cells are from 4–6 mice in each group. (F,H) n=5 in each group. Ang II, angiotensin II; INaL, late sodium current; SEM, standard error of mean.

Figure 4. Effects of moricizine on ATX II enhanced INaL, INaP, and Nav1.5 expression alteration of HL-1 cells. (A) Representative recordings of INaL from normal atrial myocytes sequentially perfused with ATX II (3 nM) and moricizine (30 µM). (B) The current density of INaL from normal atrial myocytes perfused with ATX II and moricizine. (C) Representative recordings of INaP from normal atrial myocytes perfused with ATX II and moricizine. (D) The normalized INaP from normal atrial myocytes perfused with ATX II and moricizine. (E,F) Western blot analysis of the expression of Nav1.5 in HL-1 cells. Data are presented as means ± SEM. (B,D) n=8 and cells are from 6 mice. F: n=5 in each group. ATX II, Sea anemone toxin II; INaL, late sodium current; CON, Control; INaP, peak sodium current; DMSO, dimethylsulfoxide; SEM, standard error of mean.

Figure 5. Moricizine reduced Ang II-induced upregulation of p-CaMKII in the left and right atria of the mice. (A-D) Western blot analysis of the expressions of p-CaMKII, CaMKII, and ox-CaMKII in the left atria of mice treated with saline, Ang II, or those cotreated with moricizine. (E-H) Western blot analysis of the expressions of p-CaMKII, CaMKII, and ox-CaMKII in the right atria of mice in the three groups. Data are presented as means ± SEM. n=5 in each group. Ang II, angiotensin II; ATX II, Sea anemone toxin II; CaMKII, calcium/calmodulin-dependent protein kinase-II; p-CaMKII, phospho T286 CaMKII; ox-CaMKII, oxidized CaMKII; SEM, standard error of mean.

Figure 6. Moricizine reduced the Ang II and ATX II-induced upregulation of p-CaMKII in HL-1 cells. (A-C) Western blot analysis of the expressions of p-CaMKII and CaMKII in the control, Ang II-treated, and moricizine-cotreated HL-1 cells. (D-F) Western blot analysis of the expression of p-CaMKII and CaMKII in the control, ATX II-treated and moricizine-cotreated HL-1 cells. CON group: basic culture media and 0.1% DMSO; Ang II group: 0.1% DMSO + 1 µM Ang II; Ang II + Moricizine group: 1 µM Ang II + 30 µM moricizine with DMSO solution; ATX II group: 0.1% DMSO + 3 nM ATX II; ATX II + Moricizine group: 3 nM ATX II + 30 µM moricizine with DMSO solution. Drug interventions were incubated for 24 h before harvesting. Data are presented as means ± SEM. n=5 in each group. ATX II, Sea anemone toxin II; Ang II, angiotensin II; CaMKII, calcium/calmodulin-dependent protein kinase-II; p-CaMKII, phospho T286 CaMKII; CON, Control; DMSO, dimethylsulfoxide; SEM, standard error of mean.