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Related Experiment Videos

Pitfalls when examining gap junction hemichannels: interference from volume-regulated anion channels.

Patrick Bader1, Robert Weingart

  • 1Department of Physiology, University of Bern, Bühlplatz 5, CH-3012, Bern, Switzerland.

Pflugers Archiv : European Journal of Physiology
|April 11, 2006
PubMed
Summary

This study reveals that volume-regulated anion channels (VRAC) and connexin45 hemichannels can be distinguished by their distinct voltage sensitivities and pharmacological properties, enabling precise measurement of hemichannel activity.

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Area of Science:

  • Cellular Electrophysiology
  • Ion Channel Physiology
  • Molecular Biology

Background:

  • Gap junction hemichannels, including connexin45 (Cx45) hemichannels, play crucial roles in cellular communication and homeostasis.
  • Accurate characterization of hemichannel currents is essential for understanding their physiological and pathological functions.
  • Experimental conditions can influence ion channel activity, necessitating careful optimization for reliable measurements.

Purpose of the Study:

  • To establish experimental conditions for reliably measuring currents carried by mouse connexin45 (Cx45) hemichannels in human HeLa cells.
  • To differentiate Cx45 hemichannel currents from other ion channel activities, particularly volume-regulated anion channels (VRAC).
  • To investigate the interplay between Cx45 hemichannels and VRAC under varying experimental conditions.

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Main Methods:

  • Utilized the voltage-clamp technique with whole-cell recording in human HeLa cells expressing mouse Cx45.
  • Manipulated extracellular calcium concentration ([Ca(2+)](o)) and extracellular solution osmolarity to evoke distinct currents.
  • Applied pharmacological agents, including mibefradil and 18alpha-glycyrrhetinic acid, to pharmacologically distinguish between channel types.
  • Analyzed current characteristics, including voltage sensitivity, kinetics, and inhibition patterns.

Main Results:

  • Lowering extracellular calcium evoked a variable current (I(m)) potentially related to Cx45 hemichannels.
  • Reduced extracellular osmolarity induced a current (I(VRAC)) with characteristics of VRAC, inhibited by mibefradil but not 18-alpha-glycyrrhetinic acid.
  • Minimized osmotic imbalance with reduced calcium yielded a current (I(hc)) typical of Cx45 hemichannels, inhibited by 18-alpha-glycyrrhetinic acid but not mibefradil.
  • Concomitant operation of VRAC and Cx45 hemichannels resulted in a bell-shaped conductance-voltage relationship.

Conclusions:

  • Established distinct experimental conditions to differentiate Cx45 hemichannel currents from VRAC currents.
  • Demonstrated that Cx45 hemichannels and VRAC can be selectively modulated and measured.
  • Proposed that Cx45 hemichannels and VRAC may participate in a common cellular signaling pathway.