Effect of hypoxia upon intracellular calcium concentration of human endothelial cells

Abstract

Ischemia is a situation occurring in several diseases including myocardial infarction and organ transplantation in which oxygenated blood supply is impaired. Ischemia leads to many cellular and tissue modifications, the most important one being cell death. Several explanations have been proposed to account for these modifications and cell death; among them is calcium overload. However, the influence of calcium concentration on the alteration of endothelial cell functions or viability during ischemia are still unknown. We developed here an in vitro model where human endothelial cell monolayers were submitted to hypoxia with or without reoxygenation and variation in calcium concentration was followed using a specific intracellular probe Fura 2. We observed a significant increase of [Ca2+]i during 2 h hypoxia reaching values similar to those observed during agonist stimulation of endothelial cells but far lower than values toxic for the cells. This increase was constant during the hypoxic incubation and was due mainly to an influx of extracellular calcium. Viability was also followed during hypoxia and using calcium channel blockers, we could show that there was no correlation between viability and the rise in calcium concentration. During the reoxygenation period, [Ca2+]i decreased to reach the normal value of resting cells after 45 min, suggesting that cells were still able to recover their calcium homeostasis. The use of a ketone body (beta-hydroxybutyrate) indicated that an energy deficiency was responsible for the hypoxia-induced increase in [Ca2+]i. We actually observed a 43% decrease in ATP concentration after 2 h hypoxia. This decrease was already significant after 30 min which thus precedes the changes in [Ca2+]i. These results show that during hypoxia, energy deficiency led to an increase in [Ca2+]i which is, however, too low to account for the loss of viability but which is within the range of concentrations observed during stimulation of endothelial cells. We propose that such increased intracellular calcium concentrations could play a role in the synthesis of mediators leading to the development of local inflammation.

Hypoxia-induced exocytosis of endothelial cell Weibel-Palade bodies. A mechanism for rapid neutrophil recruitment after cardiac preservation.

“…Previous studies have shown that exposure of ECs to hypoxia results in an elevation in intracellular calcium (28). In view of the association of increased cytosolic calcium with EC WP exocytosis in response to thrombin or histamine (29, 30), we considered whether exposure of ECs to hypoxia could initiate this process.…”

Histone Deacetylase 7 Associates with Hypoxia-inducible Factor 1α and Increases Transcriptional Activity

“…Therefore, it is less likely that phosphorylation of HDAC7 plays a role in translocation of HDAC7 under hypoxia. Because hypoxia causes an increase in intracellular calcium concentration in epithelial cells (42), hypoxia-induced phosphorylation of HDAC7 might be involved in stabilization of HIF-1␣⅐HDAC7 complex or export of HIF-1␣ from the nucleus to the cytoplasm.…”

Modulation of blood flow and tissue perfusion by endothelium‐derived relaxing factor

“…While EDRF synthesis is stimulated by high pH buffer through a mechanism dependent on Ca2" influx (Mitchell, de Nucci, Warner & Vane, 1991), decreases in extracellular pH could theoretically promote metabolic vasodilatation by prolonging its biological half-life (Ignarro, 1989). It remains controversial whether EDRF contributes to hypoxic vasodilatation, although hypoxia elevates [Ca2"]i in cultured endothelial cells which could potentially activate eNOS (Arnould, Michiels, Alexandre & Remacle, 1992).…”