Date on Master's Thesis/Doctoral Dissertation

12-2022

Document Type

Doctoral Dissertation

Degree Name

Ph. D.

Department

Pharmacology and Toxicology

Degree Program

Pharmacology and Toxicology, PhD

Committee Chair

Nystoriak, Matthew

Committee Co-Chair (if applicable)

Bhatnagar, Aruni

Committee Member

Bhatnagar, Aruni

Committee Member

Jones, Steven

Committee Member

LeBlanc, Amanda

Committee Member

Song, Zhao-Hui

Author's Keywords

Voltage-gated; potassium; channel dependent; cardiovascular adaptation; chronic exercise

Abstract

Exercise increases cardiac workload, escalating the demand for oxygen. The myocardial vasculature responds to the greater demand for oxygen by increasing blood flow to match the needs of the heart during augmented work. Increasing blood flow requires the coronary arteries dilate (a.k.a. vasodilation); this is mediated predominantly by vascular smooth muscle cell relaxation. Vasodilation is driven through inhibition of calcium influx into vascular smooth muscle cells. The prevention of calcium influx is largely mediated by efflux of potassium via potassium channels causing membrane hyperpolarization, which in turn closes voltage-dependent (or gated) calcium channels (VDCC). Changes in vascular smooth muscle cell membrane potential are influenced by the movement of potassium ions through K+ channels such as the voltage gated potassium (Kv) channels. Kv channels form heteromeric octomeric complexes consisting of four membrane bound α-subunits that comprise the voltage-sensitive pore complex, and associate with four intracellular auxiliary β-subunits (Κvβ). The auxiliary β-subunits are members of the aldo-keto reductase (AKR) super family, enzymes that catalytically react with carbonyl substrates. These β-subunits sense changes in oxygen availability, metabolic signal transducer ratios (e.g., NADH:NAD+) and metabolites (e.g., H2O2). In this study I investigated the role of Kv channels and their auxiliary Kvβ2 subunits in vasodilation response to conditions of altered metabolism, physiological cardiac adaptation, and myocardial blood flow in response to 4 weeks of exercise. I found that Kvβ2 is necessary to induce Kv driven vasodilation under hypoxic conditions. Loss of Kvβ2 significantly impaired exercise capacity in both naïve and 4-week exercised (exe) mice, relative to sedentary and wildtype controls. Chronic exercise also enhanced myocardial perfusion in WT mice but not Kvβ2-/- male mice. Additionally, 4-weeks of exercise significantly increased Kv1 associated Kvβ2, in proximity ligation assay experiments. In isolated arteries from SM22α-rtTA single transgenic mice, the perfusion of external 10 mM L-lactate in the presence of 10-5 M H2O2 induced significantly greater vasodilation. Interestingly, this effect was not seen in arteries from SM22α-rtTA:TRE β1 double transgenic mice. Administration of NADH and H2O2 induced significant increases in Kv channel open probability (nPo). Additionally, in vascular smooth muscle cells, isolated from SM22α-rtTA mice, externally perfused with 1 mM NADH plus of 10-5 M H2O2 we observed a significant increase in Kv nPo. Hence, we conclude that loss of Kvβ2 impairs vasodilatory capacity in response to conditions that reflect increased work. Also, exercise capacity and myocardial perfusion are impaired in the absence of Kvβ2. Additionally, the increased presence of Kvβ1 relative to Kvβ2 in the Kv channel complex opposes the vasodilatory response to metabolites and signal transducers of increased work (e.g., NADH and H2O2). In conclusion, the presence of the Kvβ2 protein in arterial myocytes is crucial for adaptation following chronic exercise training.

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