Objective: Several studies have shown that myocardial ischemia leads to functional failure of endothelial cells (EC) whereby disturbance of Ca2+ homeostasis may play an important role. The mechanisms leading to Ca2+ disbalance in ischemic EC are not fully understood. The aim of this study was to test effects of different components of simulated ischemia (glucose deprivation, anoxia, low extracellular pH (pH(o)) and lactate) on Ca2+ homeostasis in EC. Methods: Cytosolic Ca2+ (Ca(i)), cytosolic pH (pH(i)) and ATP content were measured in cultured rat coronary EC. Results: In normoxic cells 60 min glucose deprivation at pH(o) 7.4 had no effect on pH(i). It only slightly increased Ca(i) and decreased ATP content. Reduction of pH(o) to 6.5 under these conditions led to marked cytosolic acidosis and Ca(i) overload, but had no effect on ATP content. Anoxia at pH(o) 6.5 had no additional effect on Ca(i) overload, but significantly reduced cellular ATP. Addition of 20 mmol/l lactate to anoxia at pH(o) 6.5 accelerated Ca(i) overload due to faster cytosolic acidification. Acidosis-induced Ca(i) overload was prevented by inhibition of Ca2+ release channels of endoplasmic reticulum (ER) with 3 μmol/l ryanodine or by pre-emptying the ER with thapsigargin. Re-normalisation of pH(o) for 30 min led to recovery of pH(i), but not of Ca(i). Conclusion: The ischemic factors leading to cytosolic acidosis (low pH(o) and lactate) cause Ca(i) overload in endothelial cells, while anoxia and glucose deprivation play only a minor role. The ER is the main source for this Ca(i) rise. Ca(i) overload is not readily reversible. (C) 2000 Elsevier Science B.V.
Ladilov, Y., Schäfer, C., Held, A., Schäfer, M., Noll, T., & Piper, H. M. (2000). Mechanism of Ca2+ overload in endothelial cells exposed to simulated ischemia. Cardiovascular Research, 47(2), 394–403. https://doi.org/10.1016/S0008-6363(00)00108-5