β-2 Adrenergic Agonists Relax Airway Smooth Muscle Cells Through BKCa Channel Activation in a PKA- and PKG- Dependent Mechanism

Date of Award

7-2020

Degree Type

Thesis

Degree Name

Master of Science in Biomedical Sciences

First Advisor

Richard E. White, PhD

Second Advisor

Shu Zhu, MD, PhD

Third Advisor

Adwoa D. Aduonum, PhD

Abstract

Respiratory disorders, such as asthma and COPD, show their most prominent clinical effects through bronchial constriction. When bronchioles constrict they narrow the airways, trapping air in the alveoli. Beta-2 adrenergic agonists are most commonly used in the treatment of these conditions. In this study, we aim to clarify the mechanism in which beta-2 agonists induce bronchodilation. The main target of this drug is the large-conductance, voltage-, and calciumactivated potassium (BKCa) channel, which functions as a negative feedback system to induce airway smooth muscle relaxation. We hypothesized that PKA and PKG will be activated via cAMP- dependent phosphorylation to regulate BKCa channels in airway smooth muscle cells (ASMC). Using cell-attached patch clamp, we identified BKCa channels in human bronchial smooth muscle cells through its large conductance of 108pS, and its voltage dependence showing increased activity with increased depolarization (n=5). 1mM to 3mM of TEA, a specific BKCa channel inhibitor at this concentration, inhibited the BKCa channels (NPo=0, n=3), as expected. 10μM forskolin, an adenylyl cyclase activator, Increased channel activity drastically (NPo= 0.65, n=3). These experiments established the presence of BKCa channels and the cAMP-dependent phosphorylation of the channels in ASMC. The presence of 300nM of KT5720, a PKA inhibitor, show an increase in channel activity (NPo=0.95, 0.97, n=2). These results indicate that PKA plays a role in inhibiting the BKCa channels. It can be concluded that this study shows indirect evidence of PKG activating BKCa channels in ASMC.

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