Cellular Basis for Autonomic Regulation of Cardiac Arrhythmias

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PROJECT SUMMARY/ABSTRACT - Project 2 Sudden cardiac death (SCD) describes the abrupt onset of ventricular arrhythmias that kills more Americans than any other disease. These life-threatening changes in electrical activity are most often observed in people who have suffered a prior myocardial infarction (MI). Unfortunately, our ability to prevent SCD is limited by an incomplete understanding of what actually triggers the underlying arrhythmias. The surviving tissue surrounding the infarcted area of the heart, known as the border zone, is the primary sight of reentrant electrical activity that sustains these events. Electrical heterogeneities in myocytes found in the border zone and more remote areas of the myocardium create a substrate for reentry. However, the generation of arrhythmias associated with SCD is also linked to an increase in sympathetic tone and a decrease in parasympathetic tone. In fact, chronic vagal nerve stimulation (cVNS) has been shown to reduce the incidence of ventricular arrhythmias following an MI. Yet, it is not known how myocytes found in different areas of the infarcted heart respond to autonomic neurotransmitters such as norepinephrine (NE) and acetylcholine (ACh). Furthermore, there is evidence the incidence of arrhythmias is also affected by the release of co-transmitters such as neuropeptide Y (NPY) and vasoactive intestinal peptide (VIP). Our working hypothesis is that the sympathetic neurotransmitters NE and NPY, as well as the parasympathetic neurotransmitters ACh and VIP, alter the arrhythmogenic potential of the infarcted heart by regulating electrical heterogeneity as well as triggered activity in different areas. In this Project, we will address the following questions: 1) how do NPY and VIP affect the electrical properties of ventricular myocytes, 2) do sympathetic and parasympathetic neurotransmitters affect electrical heterogeneity and triggered activity of myocytes in the border zone and remote areas of the infarcted heart differently, and 3) does cVNS reduce arrhythmogenesis by remodeling the electrical and pharmacological properties of myocytes in the infarcted heart. A combination of single cell electrophysiology, molecular biology, immunocytochemistry, and biochemical techniques will be used to answer these questions. Changes occurring at the cellular level identified in this Project will be integrated with information about changes in the distribution and function of autonomic nerves observed at the whole heart level in Projects 2 and 3 of this Program Project by using a computational modeling approach to investigate the mechanistic basis for autonomic regulation of arrhythmias. The results of this project will provide the foundation from which the efficacy of targeted neuromodulation can be mechanistically assessed, leading to improved therapeutic strategies for preventing SCD.