Lactate production and release in cultured astrocytes

Intracellular lactate content and release of lactate into the surrounding medium of mouse astrocytes in primary culture was measured using the lactate dehydrogenase method. During culturing the cellular content of astrocytes decreased from 400 to 200 nmol/mg protein. The total lactate released into the extracellular space, however, amounted to 75,000 nmol/mg within 98 h, corresponding to a lactate concentration of 10 mM in the cell culture dish. In another set of experiments, cytotoxic swelling was evoked by exposure of the cells to 60 mM K+, this situation caused a 40% increase in cellular volume and an increase in the KCl content of astrocytes. Within 3 h of a change to 60 mM K+ the intracellular lactate content was increased by 100 nmol/mg (one third) and the lactate release in the extracellular space by about 2000 nmol/mg (twice as high as during exposure to 3 mM K+). However, due to the increased intracellular water content, the lactate concentration inside the cells remained unchanged. It is concluded that astrocytes produce substantial amounts of additional lactate during cytotoxic swelling. This lactate, however, is not increasing the intracellular osmolarity and most of the lactate is released into the extracellular space. Depending on the transmembrane transport mechanism it could have the capability to decrease the strong ion difference and contribute to acid shifts in the extracellular space.