Conductance and permeability of the residual state of connexin43 gap junction channels

J Gen Physiol. 2002 Feb;119(2):171-85. doi: 10.1085/jgp.119.2.171.

Abstract

We used cell lines expressing wild-type connexin43 and connexin43 fused with the enhanced green fluorescent protein (Cx43-EGFP) to examine conductance and perm-selectivity of the residual state of Cx43 homotypic and Cx43/Cx43-EGFP heterotypic gap junction channels. Each hemichannel in Cx43 cell-cell channel possesses two gates: a fast gate that closes channels to the residual state and a slow gate that fully closes channels; the transjunctional voltage (V(j)) closes the fast gate in the hemichannel that is on the relatively negative side. Here, we demonstrate macroscopically and at the single-channel level that the I-V relationship of the residual state rectifies, exhibiting higher conductance at higher V(j)s that are negative on the side of gated hemichannel. The degree of rectification increases when Cl(-) is replaced by Asp(-) and decreases when K(+) is replaced by TEA(+). These data are consistent with an increased anionic selectivity of the residual state. The V(j)-gated channel is not permeable to monovalent positively and negatively charged dyes, which are readily permeable through the fully open channel. These data indicate that a narrowing of the channel pore accompanies gating to the residual state. We suggest that the fast gate operates through a conformational change that introduces positive charge at the cytoplasmic vestibule of the gated hemichannel, thereby producing current rectification, increased anionic selectivity, and a narrowing of channel pore that is largely responsible for reducing channel conductance and restricting dye transfer. Consequently, the fast V(j)-sensitive gating mechanism can serve as a selectivity filter, which allows electrical coupling but limits metabolic communication.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Animals
  • Connexin 43 / chemistry
  • Connexin 43 / genetics
  • Connexin 43 / physiology*
  • Electric Conductivity*
  • Fluorescent Dyes / metabolism
  • Gap Junctions / chemistry
  • Gap Junctions / genetics
  • Gap Junctions / physiology*
  • HeLa Cells
  • Humans
  • Ion Channel Gating / genetics
  • Ion Channel Gating / physiology
  • Membrane Potentials / genetics
  • Membrane Potentials / physiology
  • Permeability
  • Rats
  • Transfection
  • Tumor Cells, Cultured

Substances

  • Connexin 43
  • Fluorescent Dyes