New roles for astrocytes: gap junction hemichannels have something to communicate.
Gap junctions are clusters of aqueous channels that connect the cytoplasm of adjoining cells. Each cell contributes a hemichannel, or connexon, to each cell-cell channel. The cell-cell channels are permeable to relatively large molecules, and it was thought that opening of hemichannels to the extracellular space would kill cells through loss of metabolites, collapse of ionic gradients and influx of Ca(2+). Recent findings indicate that specific non-junctional hemichannels do open under both physiological and pathological conditions, and that opening is functional or deleterious depending on the situation. Most of these studies utilized cells in tissue culture that expressed a specific gap junction protein, connexin 43. Several such examples are reviewed here, with a particular focus on astrocytes.
Department of Neuroscience, Albert Einstein College of Medicine, Bronx, NY 10461, USA. mbennett@aecom.yu.edu
Michael V L
MV
Bennett
Jorge E
JE
Contreras
Feliksas F
FF
Bukauskas
Juan C
JC
Sáez
D000818:Animals; D001253:Astrocytes / Q000502:physiology*; D020013:Calcium Signaling / Q000502:physiology; D002450:Cell Communication / Q000502:physiology*; D002490:Central Nervous System / Q000502:physiology; D017630:Connexins / Q000502:physiology*; D036563:Cyclic ADP-Ribose / Q000378:metabolism; D003593:Cytoplasm / Q000502:physiology; D017629:Gap Junctions / Q000502:physiology*; D006801:Humans; D008565:Membrane Proteins / Q000502:physiology; D015398:Signal Transduction / Q000502:physiology
D017630:Connexins; D008565:Membrane Proteins; D036563:Cyclic ADP-Ribose