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A conductance maximum observed in an inward-rectifier potassium channel
1Department of Neurobiology, Harvard Medical School, Boston, Massachusetts 02115.
The Journal of General Physiology
|September 1, 1994
Summary
Conductance in the ROMK1 potassium channel peaks at 300 mM potassium concentration. Further increases in potassium concentration reduce channel conductance, suggesting multiple ion binding sites within the pore.
Area of Science:
- Membrane biophysics
- Ion channel function
- Potassium transport
Background:
- Multi-ion pores predict a conductance maximum at high ion concentrations.
- Previous studies observed this phenomenon in gramicidin and Ca(2+)-activated K+ channels.
Purpose of the Study:
- To investigate the conductance-concentration relationship in the inward-rectifier potassium channel, ROMK1.
- To determine if ROMK1 exhibits a conductance maximum at elevated ion concentrations.
Main Methods:
- Utilized inside-out patch recording in Xenopus oocytes expressing ROMK1 channels.
- Varied potassium concentrations from 10 to 1,000 mM on both sides of the membrane.
- Eliminated internal Mg2+ to prevent outward current blockade.
Main Results:
- ROMK1 single-channel conductance increased with potassium concentration up to 300 mM, reaching a maximum of 39 pS.
- Beyond 300 mM, conductance progressively decreased, reaching ~75% of maximum at 1,000 mM K+.
- The observed conductance-concentration curve is characteristic of channels with multiple ion binding sites.
Conclusions:
- The ROMK1 channel exhibits a conductance maximum, supporting the multi-ion pore model.
- The data strongly implies the presence of multiple K(+)-occupied binding sites within the ROMK1 conduction pathway.
- This finding contributes to understanding ion permeation mechanisms in inward-rectifier potassium channels.
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