Semester

Summer

Date of Graduation

2012

Document Type

Dissertation

Degree Type

PhD

College

School of Medicine

Department

Physiology, Pharmacology & Neuroscience

Committee Chair

Han-Gang Yu.

Abstract

Encoded by hyperpolarization-activated cyclic nucleotide-gated (HCN) channels, the cardiac pacemaker current If is a major determinant of diastolic depolarization in sinus node myocytes and has a key role in the origin of heart beat. My dissertation consists of two chapters, focusing on the modulation of If and HCN channels by tyrosine phosphorylation, which is maintained by a fine balance between tyrosine kinases and phosphatases. Chapter 1 aims to investigate the role of Src tyrosine kinases in the regulation of sinus node If and HCN channels; Chapter 2 explores the modulation of ventricular If and HCN channels by a family of receptor protein tyrosine phosphatases (RPTPs).;Chapter 1 contains two sections. In Section 1, Src-mediated tyrosine phosphorylation was utilized to restore the surface expression of HCN4-D553N, a trafficking-defective mutant identified in a patient with sick sinus syndrome manifested by sinus bradycardia. The corrected D553N channel exhibited biophysical properties comparable to the wild-type HCN4 channel, suggesting a therapeutic potential of tyrosine phosphorylation for the treatment of sinus bradycardia. This part of results has been published. In Section 2, Src tyrosine kinases were found essential in facilitating the gating of HCN4 channel and activation of sinus node If, as well as increasing heart rate following the activation of beta-adrenergic receptors. In addition, these beneficial effects of Src-mediated tyrosine phosphorylation were independent of cAMP. The manuscript summarizing these results is under review.;Chapter 2 is composed of three sections. In Section 1, the tyrosine phosphatase RPTPalpha was found to exert dramatic inhibition on the activity of HCN2 channel via reducing its surface expression, which was mediated by tyrosine dephosphorylation. This work has been published. Sections 2 and 3 summarized unpublished data. In Section 2, another two tyrosine phosphatases, RPTPmu and RPTPepsilon were identified in cardiac ventricles and found to differentially regulate HCN2 channel. In Section 3, the results that RPTPepsilon inhibited 573X, a cAMP insensitive HCN4 mutant identified in patients with sick sinus syndrome and sinus bradycardia, confirm that tyrosine phosphorylation could affect HCN channel independently of cAMP.;In summary, my studies demonstrate that tyrosine phosphorylation plays a significant role in regulating the activity of If and HCN channels, in which novel modulators like RPTP and previously unrecognized mechanisms were identified, such as the cAMP-independent pathway mediating heart rate increase following the activation of beta-adrenergic receptors.

Download

Share

COinS