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Related Experiment Videos

Regulation of ROMK by extracellular cations.

H Sackin1, S Syn, L G Palmer

  • 1Department of Physiology and Biophysics, The Chicago Medical School, North Chicago, Illinois 60064, USA. sackinh@mis.finchcms.edu

Biophysical Journal
|February 13, 2001
PubMed
Summary

External potassium and cesium activate ROMK2 channels, increasing conductance. This activation involves a shift from an inactivated to an activated mode, influenced by ion concentration and potentially internal pH.

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Area of Science:

  • Molecular Biology
  • Ion Channel Physiology
  • Renal Physiology

Background:

  • The inwardly rectifying potassium channel ROMK2 (K(ir)1.1b) plays a crucial role in potassium transport.
  • Understanding the regulation of ROMK2 channel activity by external ions is essential for elucidating renal potassium handling.

Purpose of the Study:

  • To investigate the effects of external potassium (K) and cesium (Cs) on ROMK2 channel function.
  • To elucidate the mechanism underlying ROMK2 channel activation by external K and Cs.

Main Methods:

  • Whole-cell and single-channel patch-clamp recordings in Xenopus oocytes expressing ROMK2.
  • Mutagenesis studies to identify key residues involved in channel gating.
  • Manipulations of external ion concentrations (K and Cs) and analysis of channel conductance and open probability.

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Main Results:

  • Elevating external K or replacing Na with Cs significantly increased ROMK2 whole-cell conductance.
  • A rapid increase in single-channel conductance and a slower increase in channel number were observed, suggesting activation of previously inactivated channels.
  • Specific mutations, particularly at a pH-sensing site (K61), affected the transition between activated and inactivated channel states.

Conclusions:

  • External K and Cs stabilize ROMK2 in an activated mode, while low external K favors an inactivated mode.
  • The findings support a model where ROMK2 gating is directly influenced by external ions and potentially internal pH.
  • This ion-dependent gating mechanism is specific to ROMK2 and distinct from other inwardly rectifying K channels like IRK1.