The large conductance Voltage- and Ca2+ dependent K+ channels (BK) are ubiquitous membrane proteins that selectively conduct K+ ions, playing a fundamental role in a multitude of physiological processes including blood flow, uresis, immunity and neurotransmission. Very recently, defects in human BK gene have been associated to forms of generalized epilepsy (Du W. et al., 2005), a disease that affects more than 40 million people worldwide. Two striking features characterize BK channels: 1) They can be activated by both membrane depolarization and intracellular Ca2+ and 2) they possess unique permeation properties, which allow a single channel conductance of 200-300 pS while maintaining a strict K+ selectivity. This proposal will focus on both these aspects of the human BK channel (hSlo). At present, the molecular events underlying Ca2+ dependent activation and the basis for the unusually large conductance in BK channel remain unknown. We propose to address these questions by combining a variety of powerful investigative tools including electrophysiology, molecular biology, and biochemistry and fluorescence spectroscopy. The three specific aims are as follows:
Specific Aim 1 : To investigate the Ca2+ induced conformational changes of BK channel transmembrane regions. We plan to unravel the structural changes that are taking place in BK channel voltage sensing regions during Ca2+ activation, using site directed fluorescence labeling and voltage clamp fluorometry.
Specific Aim 2 : To investigate the intracellular molecular events underlying BK channel Ca2+ dependent activation. Ca2+ is believed to bind at multiple locations in the intracellular C-terminus where two functional domains that regulate the K+ conductance (RCK1 and RCK2) are expected to play a major role in BK Ca2+ activation. We have designed experiments to identify and characterize the channel Ca sensors and to shed light on the chain of molecular events that, following Ca2+ binding, lead to the opening of the channel.
In Specific Aim 3 we will investigate the energetics of high conductance in BK channels. We will use temperature and D2O solvent effects to investigate the distinctions between BK and lower conductance channel as a means for evaluating differences in permeation. These studies will help to understand the mechanism of operation of BK channels, particularly the molecular basis of their Ca2+ dependence and the unknown causes for the unusual large conductance.

Public Health Relevance

The large conductance Voltage- and Ca2+-dependent K+ channels (BK) are ubiquitous cell membrane proteins that play fundamental roles in controlling blood pressure and neuronal excitability. Elevation of the intracellular Calcium concentration activates this channel. The main objective of this proposal is to investigate the molecular events that, following the binding of Calcium to intracellular structures, lead to channel opening allowing potassium flux.

Agency
National Institute of Health (NIH)
Institute
National Institute of General Medical Sciences (NIGMS)
Type
Research Project (R01)
Project #
5R01GM082289-07
Application #
7772299
Study Section
Biophysics of Neural Systems Study Section (BPNS)
Program Officer
Rivera-Rentas, Alberto L
Project Start
2002-12-01
Project End
2012-02-29
Budget Start
2010-03-01
Budget End
2011-02-28
Support Year
7
Fiscal Year
2010
Total Cost
$358,281
Indirect Cost
Name
University of California Los Angeles
Department
Anesthesiology
Type
Schools of Medicine
DUNS #
092530369
City
Los Angeles
State
CA
Country
United States
Zip Code
90095
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Madhvani, Roshni V; Xie, Yuanfang; Pantazis, Antonios et al. (2011) Shaping a new Ca²? conductance to suppress early afterdepolarizations in cardiac myocytes. J Physiol 589:6081-92
Pantazis, Antonios; Gudzenko, Vadym; Savalli, Nicoletta et al. (2010) Operation of the voltage sensor of a human voltage- and Ca2+-activated K+ channel. Proc Natl Acad Sci U S A 107:4459-64
Pantazis, Antonios; Kohanteb, Azadeh P; Olcese, Riccardo (2010) Relative motion of transmembrane segments S0 and S4 during voltage sensor activation in the human BK(Ca) channel. J Gen Physiol 136:645-57
Yusifov, Taleh; Javaherian, Anoosh D; Pantazis, Antonios et al. (2010) The RCK1 domain of the human BKCa channel transduces Ca2+ binding into structural rearrangements. J Gen Physiol 136:189-202