A major consequence of
brain hypoxia and
hypoglycemia, which induces the detrimental effects of
stroke, is impaired
ATP supply. However, it is not yet clear to which degree reduced cellular
ATP production affects Ca(2+) homeostasis and Ca(2+) signaling of glia cells. Here we studied in cultured hippocampal astrocytes the influence of inhibition of cellular energy supply on Ca(2+) load of intracellular stores. Inhibition of glycolysis in the presence of substrates for mitochondrial respiration resulted in an average drop of intracellular
ATP levels by 35%. Inhibition of oxidative phosphorylation reduced intracellular
ATP on average by 16%. With inhibition of both glycolysis and mitochondrial
ATP production, intracellular
ATP level was drastically reduced (84%). In astrocytes in Ca(2+)-free
buffer, cytosolic [Ca(2+)](i) was dramatically increased due to inhibition of glycolysis, even in the presence of mitochondrial substrates. However, only a minor increase of [Ca(2+)](i) was observed with inhibitors of mitochondrial
ATP synthesis. Remarkably, the moderate reduction of
ATP levels found with inhibitors of glycolysis caused a severe loss of Ca(2+) from
cyclopiazonic acid (CPA)-sensitive Ca(2+) stores. Consequently, inhibition of glycolysis reduced P2Y receptor- or
thrombin receptor-evoked Ca(2+) responses on average by 95%, whereas a reduction of only 26% was found with mitochondrial inhibitors. In conclusion, glycolysis is the most important source of
ATP for the maintenance of Ca(2+) load in stores that are required for transmitter-induced signaling. These results are consistent with the concept that a local
ATP source in the vicinity of endoplasmic reticulum Ca(2+) pumps is required.