Protection against ventricular fibrillation via cholinergic receptor stimulation and the generation of nitric oxide

AbstractImplantable cardiac vagal nerve stimulators are a promising treatment for ventricular arrhythmia in patients with heart failure. Animal studies suggest the anti‐fibrillatory effect may be nitric oxide (NO) dependent, although the exact site of action is controversial. We investigated whether a stable analogue of acetylcholine could raise ventricular fibrillation threshold (VFT), and whether this was dependent on NO generation and/or muscarinic/nicotinic receptor stimulation. VFT was determined in Langendorff perfused rat hearts by burst pacing until sustained VF was induced. Carbamylcholine (CCh, 200 nmol l^–1, n = 9) significantly (P < 0.05) reduced heart rate from 292 ± 8 to 224 ± 6 b.p.m. Independent of this heart rate change, CCh caused a significant increase in VFT (control 1.5 ± 0.3 mA, CCh 2.4 ± 0.4 mA, wash 1.1 ± 0.2 mA) and flattened the restitution curve (n = 6) derived from optically mapped action potentials. The effect of CCh on VFT was abolished by a muscarinic (atropine, 0.1 μmol l⁻¹, n = 6) or a nicotinic receptor antagonist (mecamylamine, 10 μmol l⁻¹, n = 6). CCh significantly increased NOx content in coronary effluent (n = 8), but not in the presence of mecamylamine (n = 8). The neuronal nitric oxide synthase inhibitor AAAN (N‐(4S)‐4‐amino‐5‐[aminoethyl]aminopentyl‐N′‐nitroguanidine; 10 μmol l⁻¹, n = 6) or soluble guanylate cyclase (sGC) inhibitor ODQ (1H‐[1,2,4]oxadiazolo[4,3‐a]quinoxalin‐1‐one; 10 μmol l⁻¹, n = 6) prevented the rise in VFT with CCh. The NO donor sodium nitrprusside (10 μmol l^–1, n = 8) mimicked the action of CCh on VFT, an effect that was also blocked by atropine (n = 10). These data demonstrate a protective effect of CCh on VFT that depends upon both muscarinic and nicotinic receptor stimulation, where the generation of NO is likely to be via a neuronal nNOS/sGC‐dependent pathway.