Hypoxia-induced alterations in Ca(2+) mobilization in brain microvascular endothelial cells

To investigate the possible cellular mechanisms of the ischemia-induced impairments of cerebral microcirculation, we investigated the effects of hypoxia/reoxygenation on the intracellular Ca(2+) concentration ([Ca(2+)](i)) in bovine brain microvascular endothelial cells (BBEC). In the cells kept in normal air, ATP elicited Ca(2+) oscillations in a concentration-dependent manner. When the cells were exposed to hypoxia for 6 h and subsequent reoxygenation for 45 min, the basal level of [Ca(2+)](i) was increased from 32.4 to 63.3 nM, and ATP did not induce Ca(2+) oscillations. Hypoxia/reoxygenation also inhibited capacitative Ca(2+) entry (CCE), which was evoked by thapsigargin (Delta[Ca(2+)](i-CCE): control, 62.3 +/- 3.1 nM; hypoxia/reoxygenation, 17.0 +/- 1.8 nM). The impairments of Ca(2+) oscillations and CCE, but not basal [Ca(2+)](i), were restored by superoxide dismutase and the inhibitors of mitochondrial electron transport, rotenone and thenoyltrifluoroacetone (TTFA). By using a superoxide anion (O(2)(-))-sensitive luciferin derivative MCLA, we confirmed that the production of O(2)(-) was induced by hypoxia/reoxygenation and was prevented by rotenone and TTFA. These results indicate that hypoxia/reoxygenation generates O(2)(-) at mitochondria and impairs some Ca(2+) mobilizing properties in BBEC.