The goal of this project is to gain a better understanding of mechanisms that underlie metabolic coupling between myocardial oxygen demand and oxygen supply via changes in coronary blood flow to the heart. Redox-sensitive voltage-gated potassium channels (i.e., Kv1.x) in coronary vascular smooth muscle (CVSM) are known to be essential to the enhancement of myocardial blood flow (MBF) in response to increased cardiac workload. How Kv1 channel activity is enhanced in CVSM in response to metabolic signals from an active myocardium is unknown. Here, we propose an essential role for metabolic regulation of Kv1 channel activity by the tetrameric assembly of cytosolic auxiliary Kv? subunits, which are members of the aldo-keto reductase (AKR) superfamily and bind oxidized and reduced pyridine nucleotides (e.g., NAD(H)) with high affinity. Our preliminary data are consistent with the global hypothesis that interactions between NAD(H) and Kv?1 and Kv?2 impart precise control over the coupling between regional MBF with cardiac oxygen demand.
In Aim 1, we will delineate the role of coronary Kv? subunits in the regulation of the metabolic hyperemia response. To do this, we will use non-invasive myocardial contrast echocardiography (MCE) to measure MBF as a function of cardiac workload in anesthetized WT and Kv?-null animals upon administration of norepinephrine (NE). The cell-specific contribution of Kv?1 and Kv?2 in CVSM to metabolic hyperemia will be examined in double transgenic animals with inducible smooth muscle-specific expression of Kv? in null background animals. In vitro electrophysiology and myography will test the relative roles for Kv? in altering the voltage-dependence of Kv1 activation and inactivation and metabolic vasodilation, respectively.
In Aim 2, we will elucidate the mechanism of Kv?-mediated metabolic coupling. We will measure, using electrophysiology, the relative functional contribution of Kv? subunits to regulation of Kv1 activity upon specific manipulations in cellular metabolism that alter the redox ratio of NADH:NAD+ in CVSM. We will quantify changes in NADH/NAD+ redox in CVSM using genetically-encoded fluorescent biosensors and MALDI-MS imaging, and determine the role of NAD(H) turnover by Kv? catalysis in regulation of coronary vasodilation and enhancement of MBF.
In Aim 3, we will clarify the role of Kv? in cardiovascular adaptation to exercise conditioning. To do this, we will subject WT and genetically-modified animals to a forced treadmill running exercise protocol before measuring adaptations in MBF, coronary vasodilatory capacity, and Kv activation and inactivation properties.
This aim will also address the overall dependence of physiological myocardial adaptations and enhancement of exercise capacity on coronary Kv?-dependent changes in MBF.
Recent evidence indicates that defective coupling between cardiac metabolic demand and coronary vascular function contributes to myocardial ischemia in patients with heart disease. We will establish a novel paradigm of myocardial blood flow regulation by elucidating the molecular components that establish the connection between cellular metabolism and vascular smooth muscle excitability. Thus, insights generated during this project could reveal new targets for the development of more effective therapeutic strategies to prevent or reverse ischemia-related cardiac disorders.
| Nystoriak, Matthew A; Bhatnagar, Aruni (2018) Cardiovascular Effects and Benefits of Exercise. Front Cardiovasc Med 5:135 |
