title: Ca(2+) regulation of connexin 43 hemichannels in C6 glioma and glial cells.
abstract: Connexin hemichannels have a low open probability under normal conditions but open in response to various stimuli, forming a release pathway for small paracrine messengers. We investigated hemichannel-mediated ATP responses triggered by changes of intracellular Ca(2+) ([Ca(2+)](i)) in Cx43 expressing glioma cells and primary glial cells. The involvement of hemichannels was confirmed with gja1 gene-silencing and exclusion of other release mechanisms. Hemichannel responses were triggered when [Ca(2+)](i) was in the 500nM range but the responses disappeared with larger [Ca(2+)](i) transients. Ca(2+)-triggered responses induced by A23187 and glutamate activated a signaling cascade that involved calmodulin (CaM), CaM-dependent kinase II, p38 mitogen activated kinase, phospholipase A2, arachidonic acid (AA), lipoxygenases, cyclo-oxygenases, reactive oxygen species, nitric oxide and depolarization. Hemichannel responses were also triggered by activation of CaM with a Ca(2+)-like peptide or exogenous application of AA, and the cascade was furthermore operational in primary glial cells isolated from rat cortex. In addition, several positive feed-back loops contributed to amplify the responses. We conclude that an elevation of [Ca(2+)](i) triggers hemichannel opening, not by a direct action of Ca(2+) on hemichannels but via multiple intermediate signaling steps that are adjoined by distinct signaling mechanisms activated by high [Ca(2+)](i) and acting to restrain cellular ATP loss.
authors: Department of Basic Medical Sciences, Ghent University, Belgium.
authors: Elke
authors: E
authors: De Vuyst
authors: Nan
authors: N
authors: Wang
authors: Elke
authors: E
authors: Decrock
authors: Marijke
authors: M
authors: De Bock
authors: Mathieu
authors: M
authors: Vinken
authors: Marijke
authors: M
authors: Van Moorhem
authors: Charles
authors: C
authors: Lai
authors: Maxime
authors: M
authors: Culot
authors: Vera
authors: V
authors: Rogiers
authors: Romeo
authors: R
authors: Cecchelli
authors: Christian C
authors: CC
authors: Naus
authors: W Howard
authors: WH
authors: Evans
authors: Luc
authors: L
authors: Leybaert
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D000831:Animals, Newborn; D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D020013:Calcium Signaling; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2 / Q000378:metabolism; D002147:Calmodulin / Q000378:metabolism; D002478:Cells, Cultured; D018031:Connexin 43 / Q000235:genetics / Q000378:metabolism*; D005910:Glioma / Q000378:metabolism*; D006367:HeLa Cells; D006801:Humans; D009457:Neuroglia / Q000378:metabolism*; D034741:RNA, Small Interfering / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D015398:Signal Transduction; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism
chemical_list: D002147:Calmodulin; D018031:Connexin 43; D034741:RNA, Small Interfering; D000001:Calcimycin; D000255:Adenosine Triphosphate; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2; D048051:p38 Mitogen-Activated Protein Kinases; D002118:Calcium