Abstract

Hyperglycemia during brain ischemia increases the extent of injury and causes massive neuronal and astroglial death. In vitro ischemia models have shown increased opening of astroglial connexin hemichannels (HCs) and decreased coupling by gap junctions (GJC). However, the effects of high glucose concentrations during hypoxia on astrocytic Cx43 channels remain unknown. We evaluated if high glucose levels during hypoxia influence HCs and GJC during reoxygenation and whether these changes promote astroglial death. Cortical astrocytes cultured from rats or from Cx43-/- and wild type mice were subjected to reoxygenation after 3 or 6h of hypoxia with different glucose concentrations. HC activity was evaluated by ethidium uptake and GJC by intercellular dye transfer measurements. Astroglial death was evaluated by uptake of rhodamine-dextran (10kDa). After 3h of hypoxia in high glucose (12-37mM) dye uptake increased and dye coupling decreased transiently in a concentration dependent manner reaching maximal response with 27mM glucose. Six hours of hypoxia in 27mM glucose the highest increased dye uptake increase (to 400±23% of control at ~1h reoxygenation) and dye coupling reduction (to 10±2% of control at ~1h reoxygenation remained constant over 3.5h of reoxygenation and were not observed in Cx43-/- astrocytes. Moreover, 6 h hypoxia in 27mM glucose induced 43±4 % astroglial death after 6h of reoxygenation in wild type but not in Cx43-/- astrocytes. Astroglial death was prevented by Cx43 mimetic peptides (GAP26, GAP27) that blocked HCs and did not affect GJC. Thus, HCs may be a therapeutic target to reduce cell death following stroke accompanied by hyperglycemia.