Electrochemical Studies Of Cardiac Sympathetic Nerve Activity

Background:Cardiac activities are regulated by both the sympathetic and vagal nerves. The post-synaptic fibers of sympathetic nerves exert positive chronotrophic and inotrophic actions on the heart via releasing the neurotransmitter norepinephrine (NE). Under certain conditions (such myocardial infarction), hyperactivation of sympathetic nerves may induce arrhythmias and even sudden cardiac death. Therefore, the study of the functional pattern and mechanisms of sympathetic nerve activities and NE release is leadingly important both in theory and in clinics. However, till now, there is no report on the real-time monitoring of sympathetic neurotransmitter release, this condition seriously postpones the development of sympathetic nerve study.Objectives:To develop a new technique of electrochemistry-based real-time mornitoring of sympathetic neurotransmitter release in the in vivo heart and heart slice, and to study sympathetic nerve activities and the ubderlying regulatory mechanisms of NE release using this technique.Methods and results:By improving the amperometric carbon biber electrode and establish a gold fiber electrode, we invented a new technique which allows the real-time recording of cardiac sympathetic neurotransmitter norepinephrine (NE) release in the in vivo heart and heart slice. The unique superiority of this technique is that it can overcome the disturbence of heart beat on the recording. Using this technique, we studied the interactions between sympathetic nerve and vagal nerve, and the effects of hypoxia and myocardial ischemia-reperfusion on the NE release. We also identified the nature of the stimuli-evoked substance released from the sympathetic nerve terminals using the fast cyclic voltammetry and microdialysis, and the the released substance was proved to be NE. In brief, a micro gold fiber electrode was inserted into the beating myocardium. Sympathetic nerve terminal NE release was evoked by electrical stimulation of the cardiac sympathetic nerve. Hypoxia and myocardial ischemia-reperfusion procedures were performed on the rabbits. We maily observe the kinetics of NE release, modulation of cardiac sympathetic nerve activity by vagus, the effect of hypoxia on NE release induced by sympathetic nerve stimulation and effect of myocardial ischemia-reperfusion induced NE release. In the kinetics study of NE release, electrical stimulation was frequence-independent. Tthe readily releasable poor of cardiac sympathetic nerve (CSN) vesicles was depleted by electrical stimulation at 30Hz 30s and recovered after 10min. Stimulation of vagal nerve greatly attenuated the NE release from the CSN terminals. The NE oxidative current signals induced by the sympathetic stimulation recovered in 25 min. However, a hypoxia stress 50s before the electric stimulus increased electric stimulus-induced NE release. Interestingly, transient myocardial ischemia and reperfusion also induced a similar increase in the aperometric signal and recover quickly. Longer ischemia didn't induce a consistent increase of NE release.Conclusion:We established a unique technique based on the improvement of the amperometric method with gold fiber electrode which allows a real time and quantitative measurement of norepinephrine in the in vivo heart. We further identified that the kinetics of NE release from the sympathetic nerve terminal in vivo. By using this technique, we observe the sympathetic-vagus interactions and the effects of hypoxia and cardiac ischemia-reperfusion on NE release. We also identified the kinetics of NE releasing pool. The study may help to improve the development of autonomic nerve research.