Abstract
The cardiac action potential is generated by sodium and calcium channels, which depolarize the membrane, and potassium channels that repolarize the membrane. Loss of function of potassium channels hERG and KCNQ1/KCNE1, which generate IKr and IKs currents, are the most common cause of Long QT Syndrome (LQTS). LQTS is an arrhythmia disorder predisposing individuals to ventricular fibrillation and sudden cardiac death, characterized by delayed repolarization and prolonged QT interval. Some polyunsaturated fatty acid (PUFA) analogs are KCNQ1/KCNE1 activators that could reduce QT interval and lessen LQTS risks. To understand PUFA analog effects on hERG channels, I tested DHA-glycine and LIN-glycine on Xenopus oocytes expressing hERG channels, showing these PUFAs do not affect hERG channel activation, inactivation or recovery. We evaluated the arrhythmia-associated mutation R231C in KCNQ1/KCNE1 channels, measuring voltage sensor movement and ion permeability in oocytes expressing WT and R231C-mutated channels. We propose S4 is in the intermediate-activated state in both KCNQ1 R231C and KCNQ1/KCNE1 R231C channels. Finally, this project investigates structural details of KCNE1-induced rearrangements when the modulatory subunit binds KCNQ1. We mutated residue K285 on the S5-P loop and examined mutation effects on channel sensitivity to PUFA analogs with and without KCNE1 using Two-Electrode Voltage Clamp electrophysiology. The mutation causes PUFA analogs to have different effects on conductance and voltage dependence in KCNQ1 alone versus KCNQ1/KCNE1 complex, suggesting the S5-P loop changes conformation when KCNE1 binds KCNQ1. Overall, this work aims to understand the complex pharmacological interactions between PUFA analogs and potassium cardiac ion channels, and also to investigate the role of mutations and KCNE1 in modulating channel function.