title: Opening hemichannels in nonjunctional membrane stimulates gap junction formation.
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.
authors.affiliation: Department of Physiology and Biophysics, University of California at Irvine, Irvine, California, USA.
authors.forename: Derek L
authors.initials: DL
authors.lastname: Beahm
authors.forename: James E
authors.initials: JE
authors.lastname: Hall
mesh_terms: D000818:Animals; D002462:Cell Membrane / Q000502:physiology*; D002463:Cell Membrane Permeability / Q000502:physiology*; D002478:Cells, Cultured; D017630:Connexins / Q000235:genetics / Q000378:metabolism*; D004553:Electric Conductivity; D017629:Gap Junctions / Q000502:physiology*; D015640:Ion Channel Gating / Q000502:physiology*; D009865:Oocytes / Q000502:physiology*; D011994:Recombinant Proteins / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology*; D014982:Xenopus laevis
chemical_list: D017630:Connexins; D011994:Recombinant Proteins