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A pore segment in DEG/ENaC Na(+) channels.
P M Snyder1, D R Olson, D B Bucher
1Department of Internal Medicine, University of Iowa College of Medicine, Iowa City, Iowa 52242, USA. psnyder@blue.weeg.uiowa.edu
The Journal of Biological Chemistry
|September 25, 1999
Summary
Distinguishing between sodium (Na+) and other ions is vital for epithelial sodium channels (ENaC). This study reveals ENaC channels possess a unique pore structure, differing from potassium channels.
Area of Science:
- Biophysics
- Molecular Biology
- Ion Channel Physiology
Background:
- Degenerin/epithelial sodium channels (DEG/ENaC) are crucial for Na+ transport, neurotransmission, and sensory functions.
- Ion selectivity is a critical feature of DEG/ENaC channel function.
- Previous hypotheses suggested a pore structure similar to potassium (K+) channels.
Purpose of the Study:
- To investigate the pore structure of DEG/ENaC channels.
- To test the hypothesis that DEG/ENaC channels share structural similarities with K+ channels.
- To identify structural elements responsible for ion selectivity and amiloride block.
Main Methods:
- Examined accessibility of native and engineered cysteines within the putative P loop of ENaC.
- Utilized methanethiosulfonate reagents to probe the channel pore.
- Assessed the exclusion of amiloride and anionic reagents from the pore.
Main Results:
- Identified a barrier within the ENaC pore that excludes amiloride and bulky reagents.
- Discovered a selectivity-determining segment ((S/G)CS) within this barrier.
- Observed that the pore structure is inconsistent with predictions based on K+ channel models.
Conclusions:
- DEG/ENaC Na+ channels possess a novel and unique pore structure.
- The identified barrier and selectivity segment contribute to ENaC's specific ion permeation properties.
- Findings challenge existing models of ion channel pore architecture.