In hypokalemia or lowered extracellular K+ levels, human cardiac cells can become paradoxically depolarized inconsistent with the Nernst equation for K+. Such paradoxical depolarization has been observed for over thirty years. It is also crucial to the etiology of hypokalemia-induced cardiac arrhythmia. However, its molecular mechanism is not well understood. Ion selectivity of K+ channels is generally considered to be static and not changed in response to physiological stimuli. How K+ channels select K+ over other monovalent cations still remains an unsolved question. Particularly, ion selectivity and the selectivity filter of dimeric two-pore domain K+ channels (K2P) are less understood compared to those in tetrameric K+ channels. Our long-term goal is to understand physiological roles of K+ channels and molecular mechanisms of K+ channel function. The objective of this proposal is to explore functional roles of TWIK-1, the first cloned member of mammalian K2P channels in human cardiomyocytes in hypokalemia, and to characterize dynamic behaviors in ion selectivity and permeability of K2P channels. Based on studies in the past thirty years, the implications that are derived from these studies, and our preliminary studies on cloned TWIK-1 K+ channels, we hypothesize: 1) TWIK-1 K+ channels respond to challenges of lowered extracellular K+ levels and contribute to paradoxical depolarization in human cardiomyocytes in hypokalemia by changing ion selectivity and conducting inward leak Na+ currents;2) K2P channels can adjust the conformations of the selectivity filter and exhibit dynamic behaviors in ion selectivity and permeability for monovalent cations. By employing standard methods and conventional approaches in the field of ion channels and electrophysiology, we will test these hypotheses in two specific aims: 1) Investigate how TWIK-1 K+ channels regulate the resting potential and action potential of human primary cardiomyocytes in both normal and hypokalemic conditions. 2) Study ion selectivity and permeability of K2P channels for small alkali metal ions and large organic monovalent cations in the absence of intracellular K+. The proposed research will demonstrate physiological roles of TWIK-1 K+ channels in human cardiomyocytes, describe a novel mechanism that regulates cardiac excitability, provide novel insights on the understanding of paradoxical depolarization in the heart in hypokalemia, and shed light on the etiology of hypokalemia-induced cardiac arrhythmias. It will also introduce the concept of dynamic ion selectivity of K+ channels under physiological conditions, provide evidence of a flexible K+ selectivity filter, which supports or supplements well-known hypotheses regarding ion selectivity of K+ channels, and improve the understanding of ion selectivity and the selectivity filter of K2P channels.

Public Health Relevance

Hypokalemia refers to lower-than-normal blood potassium levels, which can cause human cardiac disorders. A phenomenon called paradoxical depolarization is crucial to the pathological mechanism of hypokalemia-induced cardiac disorders. The goal of this project is: 1) to understand the mechanism of such a phenomenon, by studying a gene or a genetic molecule in the human heart, which function is not known;2) to characterize novel behaviors of twelve genes or molecules in the same family. This research will provide novel insights for hypokalemia-induced cardiac disorders, possibly suggesting new methods for cardio-protection and treatment of cardiac disorders.

Agency
National Institute of Health (NIH)
Institute
National Institute of General Medical Sciences (NIGMS)
Type
Research Project (R01)
Project #
5R01GM102943-03
Application #
8706909
Study Section
Biophysics of Neural Systems Study Section (BPNS)
Program Officer
Nie, Zhongzhen
Project Start
2012-08-01
Project End
2017-07-31
Budget Start
2014-08-01
Budget End
2015-07-31
Support Year
3
Fiscal Year
2014
Total Cost
$286,726
Indirect Cost
$96,726
Name
State University of New York at Albany
Department
Biology
Type
Schools of Arts and Sciences
DUNS #
152652822
City
Albany
State
NY
Country
United States
Zip Code
12222
Chen, Haijun; Chatelain, Franck C; Lesage, Florian (2014) Altered and dynamic ion selectivity of K+ channels in cell development and excitability. Trends Pharmacol Sci 35:461-9