Extracellular K+ and Intracellular pH Allosterically Regulate Renal Kir1.1 Channels

Tadashi Doi,Bernd Fakler,Jobst H Schultz,Uwe Schulte,Uwe Brändle,Susanne Weidemann,Hans-Peter Zenner,Florian Lang,J Peter Ruppersberg

doi:10.1074/jbc.271.29.17261

Tadashi Doi, Bernd Fakler + Show 7 more

Open Access

https://doi.org/10.1074/jbc.271.29.17261

Copy DOI

Abstract

The channels that control K+ homeostasis by mediating K+ secretion across the apical membrane of renal tubular cells have recently been cloned and designated ROMK1, -2, and -3. Native apical K+ channels are indirectly regulated by the K+ concentration at the basolateral membrane through a cascade of intracellular second messengers. It is shown here that ROMK1 (Kir1.1) channels are also directly regulated by the extracellular (apical) K+ concentration, and that this K+ regulation is coupled to intracellular pH. The K+ regulation and its coupling to pH were assigned to different structural parts of the channel protein. K+ regulation is determined by the core region, which comprises the two hydrophobic segments M1 and M2 and the P region. Decoupling from pH was achieved by exchanging the N terminus of ROMK1 by that of the pH-insensitive channel IRK1 (Kir2.1). These results suggest an allosteric regulation of ROMK1 channels by extracellular K+ and intracellular pH, which may represent a novel link between K+ homeostasis and pH control.

Highlights

Terminus of ROMK1 by that of the pH-insensitive channel IRK1 (Kir2.1)
The reversible changes in current through ROMK1 channels occurred on a slow time scale and are best seen in outward current, which is carried by the constant high intracellular Kϩ concentration
The results show that extracellular Kϩ directly regulates activity of ROMK1 channels and that Kϩ regulation is controlled by intracellular pH

Summary

Introduction

Terminus of ROMK1 by that of the pH-insensitive channel IRK1 (Kir2.1). These results suggest an allosteric regulation of ROMK1 channels by extracellular K؉ and intracellular pH, which may represent a novel link between K؉ homeostasis and pH control. The common functional property of Kir channels is their inward-rectifying current-voltage relation (I-V), which may be weak or strong and which is due to a voltage-dependent block of the channel pore by intracellular polyamines (20 –23). Kϩ secretion in the kidney, which is fundamental for Kϩ homeostasis, is mediated by low conductance (35 picosiemens) weak inward-rectifier Kϩ channels found in the apical membrane of principal cells in renal collecting ducts [1, 2]. These low conductance Kϩ channels have been shown to be regulated by intracellular pH and by protein kinases [1, 3]. All clones encode weak inward-rectifier Kϩ channels, were shown to be expressed in renal tubular cells [8, 9], and are presently assumed to underlie the native renal Kϩ secretion channels [7,8,9,10]

Methods

Results

Conclusion