Specific combinations of ion channel inhibitors reduce excessive Ca2+ influx as a consequence of oxidative stress and increase neuronal and glial cell viability in vitro

Abstract

Combinations of Ca 2+ channel inhibitors have been proposed as an effective means to prevent excess Ca 2+ flux and death of neurons and glia following neurotrauma in vivo. However, it is not yet known if beneficial outcomes such as improved viability have been due to direct effects on intracellular Ca 2+ concentrations. Here, the effects of combinations of Lomerizine (Lom), 2,3-dioxo-7-(1H-imidazol-1-yl)6-nitro-1,2,3,4-tetrahydro-1-quinoxalinyl]acetic acid monohydrate (YM872), 3,5-dimethyl-1-adamantanamine (memantine (Mem)) and/or adenosine 5'-triphosphate periodate oxidized sodium salt (oxATP) to block voltage-gated Ca 2+ channels, Ca 2+ permeable a-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors, NMDA receptors and purinergic P2X 7 receptors (P2X 7 R) respectively, on Ca 2+ concentration and viability of rat primary mixed cortical (MC) cultures exposed to hydrogen peroxide (H 2 O 2 ) insult, were assessed. The contribution of ryanodine-sensitive intracellular stores to intracellular Ca 2+ concentration was also assessed. Live cell calcium imaging revealed that a 30 min H 2 O 2 insult induced a slow increase in intracellular Ca 2+ , in part from intracellular sources, associated with loss of cell viability by 6 h. Most combinations of inhibitors that included oxATP significantly decreased Ca 2+ influx and increased cell viability when administered simultaneously with H 2 O 2 . However, reductions in intracellular Ca 2+ concentration were not always linked to improved cell viability. Examination of the density of specific cell subpopulations demonstrated that most combinations of inhibitors that included oxATP preserved NG2+ non-oligodendroglial cells, but preservation of astrocytes and neurons required additional inhibitors. Olig2 + oligodendroglia and ED-1 + activated microglia/macrophages were not preserved by any of the inhibitor combinations. These data indicate that following H 2 O 2 insult, limiting intracellular Ca 2+ entry via P2X 7 R is generally associated with increased cell viability. Protection of NG2+ non-oligodendroglial cells by Ca 2+ channel inhibitor combinations may contribute to observed beneficial outcomes in vivo.