Metabolic inhibition induces opening of unapposed connexin 43 gap junction hemichannels and reduces gap junctional communication in cortical astrocytes in culture.
Rat cortical astrocytes in pure culture are functionally coupled to neighboring cells via connexin (Cx) 43 gap junctions under ordinary conditions. Small fluorescent molecules such as Lucifer yellow (LY) pass between cell interiors via gap junctions, but do not enter the cells when externally applied. Subjecting rat and mouse cortical astrocytes to "chemical ischemia" by inhibition of glycolytic and oxidative metabolism induced permeabilization of cells to Lucifer yellow and ethidium bromide before loss of membrane integrity determined by dextran uptake and lactate dehydrogenase release. The gap junction blockers octanol and 18alpha-glycyrrhetinic acid markedly reduced dye uptake, suggesting that uptake was mediated by opening of unapposed hemichannels. Extracellular La(3+) also reduced dye uptake and delayed cell death. The purinergic blocker, oxidized ATP, was ineffective. Astrocytes isolated from mice with targeted deletion of the Cx43 coding DNA exhibited greatly reduced dye coupling and ischemia-induced dye uptake, evidence that dye uptake is mediated by Cx43 hemichannels. Dye coupling was reduced but not blocked by metabolic inhibition. Blockade of lipoxygenases or treatment with free radical scavengers reduced dye uptake by rat astrocytes, suggesting a role for arachidonic acid byproducts in hemichannel opening. Furthermore, permeabilization was accompanied by reduction in ATP levels and dephosphorylation of Cx43. Although hemichannel opening would tend to collapse electrochemical and metabolic gradients across the plasma membrane of dying cells, healthy cells might rescue dying cells by transfer of ions and essential metabolites via Cx43 gap junctions. Alternatively, dying astrocytes might compromise the health of neighboring cells via Cx43 gap junctions, thereby promoting the propagation of cell death.
Contreras
Jorge E
JE
Departamento de Ciencias Fisiológicas, Facultad de Ciencias Biológicas, Pontificia Universidad Católica de Chile, Santiago 340, Chile.
Sánchez
Helmut A
HA
Eugenin
Eliseo A
EA
Speidel
Dina
D
Theis
Martin
M
Willecke
Klaus
K
Bukauskas
Feliksas F
FF
Bennett
Michael V L
MV
Sáez
Juan C
JC
D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D001253:Astrocytes / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism; D002478:Cells, Cultured; D018031:Connexin 43 / Q000737:chemistry* / Q000378:metabolism*; D003911:Dextrans / Q000493:pharmacokinetics; D004996:Ethidium / Q000494:pharmacology; D005456:Fluorescent Dyes / Q000494:pharmacology; D016166:Free Radical Scavengers; D017629:Gap Junctions / Q000737:chemistry* / Q000378:metabolism; D006034:Glycyrrhetinic Acid / Q000031:analogs & derivatives* / Q000378:metabolism; D006801:Humans; D007364:Intercalating Agents / Q000494:pharmacology; D007477:Ions; D007546:Isoquinolines / Q000378:metabolism; D007770:L-Lactate Dehydrogenase / Q000493:pharmacokinetics; D007811:Lanthanum / Q000378:metabolism; D016859:Lipoxygenase Inhibitors / Q000494:pharmacology; D051379:Mice; D011485:Protein Binding; D051381:Rats; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D013997:Time Factors
D018031:Connexin 43; D003911:Dextrans; D005456:Fluorescent Dyes; D016166:Free Radical Scavengers; D007364:Intercalating Agents; D007477:Ions; D007546:Isoquinolines; D016859:Lipoxygenase Inhibitors; D011993:Recombinant Fusion Proteins; C119129:18alpha-glycyrrhetinic acid; D007811:Lanthanum; D000255:Adenosine Triphosphate; C017475:lucifer yellow; D007770:L-Lactate Dehydrogenase; D004996:Ethidium; D006034:Glycyrrhetinic Acid; D002118:Calcium