Mechanisms of ranolazine pretreatment in preventing ventricular tachyarrhythmias in diabetic db/db mice with acute regional ischemia–reperfusion injury

Figures

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  Figure 1. In vivo electrophysiological study. (A) Summary of in vivo ventricular tachycardia (VT) inducibility. (B) Percentage of VT episodes by pacing protocols. The number and percentage of pacing-induced VT were shown in the middle of each bar. Pretreatment of ranolazine significantly reduced the inducibility ratio of VT episodes by both burst pacing and extrastimulus pacing protocols in db/db and db/+ groups. (C) Distribution of the severity of VT, plotted as the number of beats of VT. The number and percentage of VT episodes were shown on the top of each bar. The db/db C group had higher percentage of long VT (> 30 beats) than other groups (P = 0.031). (D) A representative example of pseudo-electrocardiogram showing extrastimulus pacing-induced VT in a db/db C mouse heart.

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  Figure 2. Effects of ranolazine therapy on APD80 and CaiTD80. (A) Scattered graphs of APD80 and CaiTD80 at pacing cycle length (PCL) of 200 ms and 100 ms. Orange dots and numbers indicate the mean values. Ranolazine significantly shortened APD80 and CaiTD80 in db/db mice. (B) Representative APD80 and CaiTD80 maps at pacing cycle length (PCL) = 200 and 100 ms.

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  Figure 3. Effects of ranolazine therapy on intracellular Ca2+ (Cai) decay. (A) Scattered graphs of Cai decay tau values among the four groups and between the ischemia–reperfusion (IR) and non-IR zones. Orange dots and numbers indicate the mean values. Ranolazine therapy shortened the tau value in db/db mice and ameliorated the differences of tau values between the non-IR and IR zones in db/db mice. (B) Representative examples of Cai decay in the non-IR and IR zones among the four groups.

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  Figure 4. Representative examples of isochrone maps at a pacing cycle length (PCL) from 200 to 60 ms in four groups. Black dashed arrows indicate the directions of CVnon-IR (conduction velocity (CV) along the atrioventricular ring) and CVIR (CV pointing to the apical ischemia–reperfusion zone) measurements; numbers in right subpanels are CV (cm/s). Right subpanels show the anatomical structure and orientation of optical maps. Ranolazine therapy ameliorated CVIR slowing to ameliorate conduction inhomogeneity (see Table 1). Red line, left coronary artery; dashed line, margin of IR zone; LAA, left atrial appendage; LV, left ventricle; RV, right ventricle.

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  Figure 5. Mechanisms of ventricular tachycardia (VT) induction in a db/db C mouse heart with ischemia–reperfusion (IR) injury. (A) IR creation. Ischemia zone distal to the tie is shown in gray, and recovered after removal of the ligature in red. (B) Mapping field. Yellow dotted line indicates the margin of the IR zone. LV, left ventricle; RV, right ventricle. (C) Membrane voltage (Vm) traces showing the initiation of VT by S1-S4 pacing. Red arrow indicates fragmented Vm transient during rotor anchoring at site “a”. (D) Isochrone maps corresponding to the period marked by a red square in C. The number below each frame is the time (ms) with the onset of data acquisition as time zero. White arrows indicate the directions of wavefront propagation. Left subpanel shows the anatomical structure of the mapping filed. Red line, left coronary artery; dashed line, margin of IR zone. (E) Phase singularity (left) and Vm alternans (right) maps. A phase singularity (site “a”) was formed on a nodal line during VT. (F) Summary of the VA inducibility result.

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  Figure 6. Representative examples of the Western blots result of pThr17-phospholamban (PLB-T), calsequestrin 2 (CASQ2) and voltage-gated sodium channel (SCN5A). Scattered graphs represent densitometric values normalized to the corresponding GAPDH. Orange dots and numbers indicated the mean values.

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  Figure 7. Whole-cell late Na+ currents (INa,L) recording. (A) Scattered graphs of mean INa,L. The graph shows the comparisons of the current density among four groups and between the ischemia–reperfusion (IR) and non-IR zones. Orange dots and numbers indicated the mean values. Student’s t-test for comparisons between the IR and non-IR zones and one-way repeated measures analysis of variance with post hoc least significant difference analysis for comparisons among the four groups. The db/db cardiomyocytes expressed a greater INa,L density than the db/+ cells. Ranolazine therapy significantly decreased the density of INa,L in both db/db mice and db/+ mice. (B) Representative INa,L traces of the cardiomyocytes among the four groups.