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Voltage gating and permeation in a gap junction hemichannel
E B Trexler1, M V Bennett, T A Bargiello
1Department of Neuroscience, Albert Einstein College of Medicine, New York 10461-1602, USA.
Summary
Connexin 46 (Cx46) hemichannels exhibit unique voltage-gated opening and closing mechanisms. These channels allow significant cation flow at physiological voltages, impacting cellular communication.
Area of Science:
- Cellular Biology
- Biophysics
- Ion Channel Physiology
Background:
- Gap junction channels facilitate direct cell-to-cell communication via connexons.
- Most connexins require apposing hemichannels to open, but Cx46 shows potential for depolarization-induced opening.
Purpose of the Study:
- To investigate the gating mechanisms of rat Cx46 hemichannels using single-channel recordings.
- To characterize the voltage dependence and kinetics of Cx46 hemichannel opening and closing.
Main Methods:
- Single-channel recording in Xenopus oocytes expressing rat Cx46.
- Analysis of channel conductance states (gammaopen, gammasub, gammaclosed).
- Assessment of ion selectivity and pore size using permeability studies.
Main Results:
- Cx46 hemichannels display two distinct voltage-gating mechanisms.
- Depolarization causes partial closure to a substate (gammasub), while hyperpolarization induces slow closure to a fully closed state (gammaclosed).
- Cx46 hemichannels are cation-selective, possess large unitary conductance (~300 pS), and a pore diameter of ~8.5 Å.
Conclusions:
- Cx46 hemichannels possess unique gating properties enabling opening even without apposing hemichannels.
- These channels are permeable to cations and open at physiological voltages, suggesting a role in cellular ion flux.
- The findings provide insights into the functional diversity of connexin hemichannels in cellular signaling.