Inhibition of KCa3.1 Channels Suppresses Atrial Fibrillation via the Attenuation of Macrophage Pro-inflammatory Polarization in a Canine Model With Prolonged Rapid Atrial Pacing.

Aims: To investigate the role of KCa3. 1 inhibition in macrophage pro-inflammatory polarization and vulnerability to atrial fibrillation (AF) in a canine model with prolonged rapid atrial pacing. Materials and Methods: Twenty beagle dogs (weighing 8-10 kg) were randomly assigned to a sham group (n = 6), pacing group (n = 7) and pacing+TRAM-34 group (n = 7). An experimental model of AF was established by rapid pacing. TRAM-34 was administered to the Pacing+TRAM-34 group by slow intravenous injection (10 mg/kg), 3 times each day. After 7 days of pacing, the electrophysiology was measured in vivo. The levels of interleukin-1ß (IL-1ß), monocyte chemotactic protein-1 (MCP-1), tumor necrosis factor-α (TNF-α), CD68, c-Fos, p38, and NF-κB p65 in both atriums were measured by Western blotting, and the levels of inducible nitric oxide synthase (iNOS) and arginase1 (Arg-1) were measured by real-time PCR. Macrophage and KCa3.1 in macrophage in the atrium were quantized following double labeled immunofluorescent. Results: Greater inducibility of AF, an extended duration of AF and lower atrial effective refractory period (AERP) were observed in the pacing group compared with those in the sham group. Both CD68-labeled macrophage and the expression of KCa3.1 in macrophage were elevated in the pacing group and inhibited by TRAM-34, led to higher iNOS expression, lower Arg-1 expression, elevated levels of IL-1ß, MCP-1, and TNF-α in the atria, which could be reversed by TRAM-34 treatment (all P < 0.01). KCa3.1 channels were possibly activated via the p38/AP-1/NF-κB signaling pathway. Conclusions: Inhibition of KCa3.1 suppresses vulnerability to AF by attenuating macrophage pro-inflammatory polarization and inflammatory cytokine secretion in a canine model with prolonged rapid atrial pacing.

Left Stellate Ganglion Ablation Inhibits Ventricular Arrhythmias through Macrophage Regulation in Canines with Acute Ischemic Stroke.

AIMS: To investigate the potential mechanism of ventricular arrhythmias (VAs) after acute ischemic stroke and explore the effects of left stellate gangling (LSG) ablation on VAs induced by stroke in canines. Materials and Methods: Twenty canines were randomly divided into the sham-operated group (n=6), AS group (n=7) and SGA group (n=7). Cerebral ischemic model was established in the AS group and the SGA group by right acute middle cerebral artery occlusion (MCAO). LSG ablation was performed in the SGA group as soon as MCAO. After 3 days, atrial electrophysiology and neural activity were measured in vivo. The levels of norepinephrine (NE) in plasma and ventricle were detected by ELISA. The levels of monocyte chemotactic protein-1 (MCP-1), tumor necrosis factor-α (TNF-α) and NF-κB p65 in ventricle were detected by western blotting. The pro-inflammatory polarization of macrophages in ventricle was detected by immunofluorescence. Results: Higher ventricular tachycardia (VT) inducibility and lower ventricular fibrillation threshold (VFT) were observed in the AS group compared with those in the sham-operated group, associated with higher LSG activity and NE levels, increased number of M1 macrophages and secretion of inflammatory cytokines in ventricle (all P<0.001). Compared with the AS group, the SGA group had lower VT inducibility and higher VFT, combined with lower NE levels, and reduced number of M1 macrophages and secretion of inflammatory cytokines in ventricle (all P<0.001). Conclusion: LSG ablation could reduce VAs vulnerability after acute stroke by preventing the macrophages polarization and activation induced by sympathetic hyperactivity.

A brain-stellate ganglion-atrium network regulates atrial fibrillation vulnerability through macrophages in acute stroke.

AIMS: New-onset atrial fibrillation (AF) is frequently observed following acute stroke. The aim of this study was to investigate the effects of the brain-stellate ganglion-atrium network on AF vulnerability in a canine model with acute middle cerebral artery occlusion (MCAO). MATERIALS AND METHODS: Twenty-six dogs were randomly divided into the sham-operated group (n = 6), acute stroke (AS) group (n = 7), stellate ganglion ablation (SGA) group (n = 6) and clodronate liposome (CL) group (n = 7). In the sham-operated group, dogs received craniotomy without MCAO. Cerebral ischemic model was established in AS dogs by right MCAO. Right MCAO along with SGA and CL injection into the atrium was performed in SGA and CL dogs, respectively. After 3 days, atrial electrophysiology, neural activity, and the phenotype and function of macrophages in the atrium were studied in all the dogs. KEY FINDINGS: Higher AF inducibility (24.4 ±â€¯4.4% versus 4.4 ±â€¯2.2%, P < 0.05) and AF duration (15.7 ±â€¯3.8 s versus 2.6 ±â€¯1.1 s, P < 0.05) were observed in the AS group compared with the sham-operated group, and were associated with increased left stellate ganglion activity, higher macrophage infiltration and higher levels of inflammatory cytokines in the atrium. SGA or CL injection sharply suppressed AF inducibility (5.5 ±â€¯2.7% versus 24.4 ±â€¯4.4%; 5.3 ±â€¯3.2% versus 24.4 ±â€¯4.4%, both P < 0.05) and AF duration (2.9 ±â€¯1.2 s versus 15.7 ±â€¯3.8 s; 3.6 ±â€¯1.0 s versus 15.7 ±â€¯3.8 s, both P < 0.05) in canines with acute stroke. SIGNIFICANCE: A brain-stellate ganglion-atrium network may increase AF vulnerability through macrophage activation after acute stroke.