Dual regulation of astrocyte gap junction hemichannels by growth factors and a pro-inflammatory cytokine via the mitogen-activated protein kinase cascade.
Evidence that glutamate and ATP release from astrocytes can occur via gap junction hemichannels (GJHCs) is accumulating. However, the GJHC is still only one possible release mechanism and has not been detected in some studies, although this may be because the levels were below those detectable by the system used. Because of these conflicting results, we hypothesized that release from astrocyte GJHCs might depend on different astrocyte states, and screened for factors affecting astrocyte GJHC activity by measuring fluorescent dye leakage via GJHCs using a conventional method for GJHC acivation, i.e. removal of extracellular divalent cations. Astrocytes cultured in Dulbecco's minimal essential medium containing 10% fetal calf serum, a medium widely used for astrocyte studies, did not show dye leakage, whereas those cultured in a defined medium showed substantial dye leakage, which was confirmed pharmacologically to be due to GJHCs and not to P2x7 receptors. EGF and bFGF inhibited the GJHC activity via the mitogen-activated protein kinase cascade, and the effect of the growth factors was reversed by interleukin-1beta. These factors altered GJHC activity within 10 min, but did not affect connexin 43 expression. GJHC activity in hippocampal slice culture preparations was measured using the same methods and found to be regulated in a similar manner. These results indicate that astrocyte GJHC activity is regulated by brain environmental factors.
Morita
Mitsuhiro
M
Laboratory of Cellular Neurobiology, School of Life Science, Tokyo University of Pharmacy and Life Science, Tokyo, Japan. mritam@ls.toyaku.ac.jp
Saruta
Chihiro
C
Kozuka
Nagisa
N
Okubo
Yoshiumi
Y
Itakura
Makoto
M
Takahashi
Masami
M
Kudo
Yoshihisa
Y
D000818:Animals; D001253:Astrocytes / Q000166:cytology / Q000378:metabolism*; D018929:Cell Culture Techniques; D002478:Cells, Cultured; D018031:Connexin 43 / Q000378:metabolism; D004815:Epidermal Growth Factor / Q000502:physiology*; D005260:Female; D016222:Fibroblast Growth Factor 2 / Q000502:physiology*; D017629:Gap Junctions / Q000378:metabolism*; D018698:Glutamic Acid / Q000378:metabolism; D006624:Hippocampus / Q000166:cytology / Q000378:metabolism; D053583:Interleukin-1beta / Q000502:physiology*; D008297:Male; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D015290:Second Messenger Systems / Q000502:physiology; D015398:Signal Transduction / Q000502:physiology
D018031:Connexin 43; C500216:GJA1 protein, human; D053583:Interleukin-1beta; D016222:Fibroblast Growth Factor 2; D018698:Glutamic Acid; D004815:Epidermal Growth Factor; D020928:Mitogen-Activated Protein Kinases