Astrocytes are numerous neuroglial cells of the central nervous system, which communicate with neighbouring cells when excited via various GPCRs at the astrocytic membrane and the ensuing changes in second messengers. Astrocytes are positioned between neurons and blood vessels, hence are ideally positioned to uptake glucose from the endothelium of brain capillaries. Recently, new data has added support for the hypothesis that astrocytes are passing lactate to neurons. Lactate is a metabolite produced in astrocytes by aerobic glycolysis. Neurons likely use lactate as a preferential source of energy. The aim of our research was to determine whether the level of intracellular lactate increases following the stimulation of adrenergic receptors by noradrenaline, while we: 1) inhibited glycolysis by 2-DG, 2) inhibited degradation of glycogen by DAB, 3) blocked the citric acid cycle with 3-NPA and 4) blocked LDH by Oxamate, which inhibits the conversion of pyruvate to lactate. We measured changes in cytosolic lactate in single living astrocytes in real time. For this we used the FRET nanosensor Laconic. By pharmacological modulation of distinct segments of metabolism, the results revealed that glucose uptake is essential for the production of lactate in astrocytes upon adrenergic activation. We have also shown that practically all lactate increase upon adrenergic activation originates from glycogen. Glycolysis appears an essential energy source for astrocytes when the citric acid cycle was blocked. When the enzyme LDH was inhibited, no lactate was formed, confirming the view that lactate produced upon adrenergic activation in astrocytes is formed via pyruvate.
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