IRK1 inward rectifier K(+) channels exhibit no intrinsic rectification.

Area of Science:

• Molecular Biology
• Electrophysiology
• Ion Channel Physiology

Background:

• Depolarization-induced outward IRK1 currents exhibit relaxation, leading to strong inward rectification.
• Previous interpretations suggested intrinsic channel gating or cation enhancement of gating as causes for rectification.
• Extracellular K(+)-sensitive relaxation of IRK1 inward current was compared to Shaker channel C-type inactivation.

Purpose of the Study:

• To investigate the underlying mechanisms of IRK1 current relaxations and inward rectification.
• To determine if observed phenomena reflect intrinsic channel properties or experimental artifacts.
• To define optimal experimental conditions for studying IRK1 channels.

Main Methods:

• Patch-clamp electrophysiology on cells expressing IRK1 channels.
• Perfusion of membrane patches with solutions devoid of Mg(2+) and polyamines.
• Analysis of current relaxations under varying extracellular K(+) concentrations.
• Identification and quantification of impurities in common recording solution constituents (HEPES, EDTA).

Main Results:

• Current relaxations previously attributed to IRK1 gating were found to be caused by impurities like hydroxyethylpiperazine and ethylenediamine.
• IRK1 channels exhibit essentially ohmic behavior at the macroscopic level under purified conditions.
• The observed voltage-dependent phenomena are explained by the high affinity of the IRK1 pore for cations, not intrinsic gating.

Conclusions:

• The intrinsic gating of IRK1 channels does not inherently cause significant inward rectification or voltage-dependent current relaxations.
• Impurities in standard electrophysiology solutions can significantly alter the measured properties of ion channels, including IRK1.
• This study clarifies the true nature of IRK1 channel behavior and provides guidelines for accurate experimental design.