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Inward rectification by polyamines in mouse Kir2.1 channels: synergy between blocking components.
Lai-Hua Xie1, Scott A John, James N Weiss
1Cardiovascular Research Laboratory, Department of Medicine (Cardiology), David Geffen School of Medicine at University of California, Los Angeles, Los Angeles, CA 90095, USA.
The Journal of Physiology
|May 13, 2003
Summary
Polyamines like spermine block Kir2.1 channels through surface charge reduction and pore block. These mechanisms involve specific binding to channel charges, influencing conductance and block kinetics.
Area of Science:
- Biophysics
- Molecular Biology
- Ion Channel Physiology
Background:
- Polyamines are essential molecules that regulate cellular processes.
- Kir2.1 channels are inward-rectifier potassium channels crucial for membrane potential.
- Polyamines are known to modulate Kir2.1 channel function through distinct mechanisms.
Purpose of the Study:
- To elucidate the interplay between surface charge reduction and open channel block by polyamines on Kir2.1 channels.
- To determine the roles of polyamine charge, length, and specific channel residues in these blocking mechanisms.
- To develop a mechanistic model for polyamine block of Kir2.1 channels.
Main Methods:
- Macroscopic current recordings from Xenopus oocyte giant patches.
- Single-channel current recordings from COS7 cells expressing wild-type and mutant Kir2.1 channels.
- Systematic variation of polyamine length and charge, and mutation of key acidic residues (E224, E299, D172).
Main Results:
- Surface charge reduction by polyamines requires specific binding and is dependent on polyamine length.
- Open channel block comprises fast and slow kinetic components, differentially sensitive to polyamine charge and length.
- Mutating E224 and E299 abolished surface charge reduction and the fast pore block component.
- Mutating D172 weakened both pore block components without affecting surface charge reduction.
Conclusions:
- Polyamines block Kir2.1 channels via a coordinated mechanism involving surface charge reduction and open channel block.
- Specific acidic residues (E224, E299, D172) in the cytoplasmic pore play critical roles in mediating these blocking effects.
- A molecular model suggests polyamines bind to E224 and E299, facilitating interaction with D172 for pore occlusion.