Opening hemichannels in nonjunctional membrane stimulates gap junction formation

Biophys J. 2004 Feb;86(2):781-96. doi: 10.1016/S0006-3495(04)74154-5.

Abstract

We studied gap junction formation in pairs of Xenopus laevis oocytes expressing connexins that form functional hemichannels and found no correlation between junctional conductance (G(j)) and whole-cell hemichannel conductances (G(hemi)) within the first few hours of pairing. However, opening hemichannels to a threshold current stimulated a rapid G(j) increase. Moreover, cx46 hemichannel current stimulated cx40 G(j) even though cx40 and cx46 do not form heteromeric or heterotypic gap junctions. Initial growth rate and final steady-state level of stimulated G(j) were proportional to the product of hemichannel conductances. External calcium affected the growth rate of stimulated G(j) but not the final steady-state value. Time constants of formation were short in low [Ca(2+)](out) (3 min in 200 micro M Ca(2+)) and long in high [Ca(2+)](out) (15 min in 1 mM Ca(2+)), but in oocyte pairs pretreated with lectins to reduce steric hindrance imposed by large membrane glycoproteins the time constant was short and Ca(2+)-independent. We suggest that hemichannel activity stimulates G(j) by collapsing the extracellular volume between membranes to allow the end-to-end binding between hemichannels. These studies suggest the possibility that functional hemichannels could trigger or enhance junctional formation in vivo in response to appropriate stimuli.

Publication types

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

MeSH terms

  • Animals
  • Cell Membrane / physiology*
  • Cell Membrane Permeability / physiology*
  • Cells, Cultured
  • Connexins / genetics
  • Connexins / metabolism*
  • Electric Conductivity
  • Gap Junctions / physiology*
  • Ion Channel Gating / physiology*
  • Oocytes / physiology*
  • Recombinant Proteins / metabolism
  • Signal Transduction / physiology*
  • Xenopus laevis

Substances

  • Connexins
  • Recombinant Proteins