Chemogenetic activation of cholinergic intrinsic cardiac ganglia improves border zone oxygenation and reduces arrhythmias during acute local ischemia.

BACKGROUND: Current therapeutic strategies for acute myocardial infarction rely on reperfusion and pharmacological management, which are typically administered hours after an event. Activation of the cardiac cholinergic efferents superior to the heart soon after a coronary occlusion has shown promise as a potential therapy to reduce arrhythmias and improve ventricular function. We tested whether selective activation of cholinergic neurons within the intrinsic cardiac ganglia (ICG) would also reduce arrhythmias and improve oxygenation of ischemic border zone tissue after an acute coronary occlusion.

METHODS: Designer Receptors Exclusively Activated by Designer Drugs (DREADDs) were selectively expressed in cholinergic neurons of the ICG via pericardial sac injections of an HM3Dq DREADDs virus in transgenic rats that expressed Cre recombinase in cholinergic neurons. Cholinergic ICG neurons were activated using the synthetic DREADDs ligand clozapine-N-oxide (CNO). Heart rate reductions after intraperitoneal injection of CNO confirmed downstream effect of DREADDs-mediated cholinergic ICG activation in ECG telemetry studies. The effect of cholinergic ICG activation on PR interval, arrhythmia burden, ischemic border zone tissue oxygenation and epicardial NADH fluorescence 20 min after ligation of the left anterior descending coronary artery (LAD) was then studied in excised perfused hearts of DREADDS-expressing rats and rats that did not receive the HM3Dq DREADDs virus.

RESULTS: LAD ligation resulted in a well defined ischemic zone that encompassed a large portion of the left ventricle, where pO2 in the center of the ischemic zone typically dropped to 0 mmHg within 10 s. Subsequent DREADDs-mediated cholinergic ICG activation prolonged the PR interval from 39.13 ± 6.17 ms to 42.46 ± 6.87 ms and lowered the incidence of arrhythmia from 0.9398 ± 0.5063  min - 1 to .5727 ± 0.3103  min - 1 . DREADDs-mediated cholinergic ICG activation also increased ischemic border zone pO2 from 42.13 ± 49.82 mmHg to 82.25 ± 66.87 mmHg and NADH fluorescence trended lower in the ischemic zone, indicating increased mitochondrial oxidation. These effects were blocked when the muscarinic antagonist atropine was administered before CNO.

CONCLUSION: Results indicate that selective stimulation of cholinergic ICG neurons could improve local delivery of oxygen to the ischemic border zone soon after a coronary occlusion and reduce arrhythmia burden through a muscarinic-dependent mechanism, supporting further studies of the intrinsic cardiac cholinergic network as a therapeutic target for early intervention before reperfusion therapy to activate cardioprotective pathways.