Author:

Keywords:

Calcium, Glutamate, Connexon, Eicosanoids, Gliotransmitter, Glial cells, Science & Technology, Life Sciences & Biomedicine, Cell Biology, GAP-JUNCTION CHANNELS, ATP RELEASE, EXTRACELLULAR CALCIUM, CX43 HEMICHANNELS, ARACHIDONIC-ACID, KINASE-II, PROTEIN, ASTROCYTES, EXPRESSION, PANNEXIN-1, Adenosine Triphosphate, Animals, Animals, Newborn, Calcimycin, Calcium Signaling, Calcium-Calmodulin-Dependent Protein Kinase Type 2, Calmodulin, Cells, Cultured, Connexin 43, Glioma, HeLa Cells, Humans, Neuroglia, RNA, Small Interfering, Rats, Rats, Sprague-Dawley, Signal Transduction, p38 Mitogen-Activated Protein Kinases, Hela Cells, 0601 Biochemistry and Cell Biology, 0606 Physiology, 1116 Medical Physiology, Biochemistry & Molecular Biology, 3101 Biochemistry and cell biology, 3208 Medical physiology

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.