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Inward rectification of the IRK1 K+ channel reconstituted in lipid bilayers
A Aleksandrov1, B Velimirovic, D E Clapham
1Department of Pharmacology, Mayo Foundation, Rochester, Minnesota 55905, USA.
Biophysical Journal
|June 1, 1996
Summary
Inwardly rectifying potassium (IRK1) channels exhibit intrinsic voltage-dependent rectification. This mechanism, independent of external factors, is further modulated by cytoplasmic factors like magnesium and spermine.
Area of Science:
- Biophysics
- Ion Channel Physiology
- Molecular Biology
Background:
- Inward rectification in potassium channels is a crucial physiological process.
- Understanding the underlying mechanisms of inward rectification is essential for comprehending cellular excitability.
Purpose of the Study:
- To investigate the intrinsic rectification mechanisms of Inwardly Rectifying Potassium (K+) channels (IRK1).
- To differentiate between intrinsic and extrinsic factors contributing to IRK1 channel rectification.
Main Methods:
- Incorporation of IRK1 channels into artificial lipid bilayers.
- Expression of IRK1 channels in Xenopus laevis oocytes and subsequent membrane vesicle fusion.
- Electrophysiological recordings to measure single channel conductance and rectification properties.
Main Results:
- IRK1 channels demonstrated voltage-dependent inward rectification intrinsically, without requiring divalent ions or charged regulators.
- Single channel conductance was measured at 21 pS in 140 mM symmetrical [K+], varying with the square root of external [K+].
- Cytoplasmic Mg2+ and spermine significantly enhanced rectification but did not act through simple pore block.
Conclusions:
- IRK1 channels possess an inherent mechanism for inward rectification.
- A novel, fast gating process, distinct from slow gating, is proposed to contribute to rectification, potentially amplified by cytoplasmic Mg2+ and polyamine binding.