Amino acid content of rat cerebral astrocytes adapted to hyperosmotic medium in vitro.

Rat cerebral astrocytes from confluent primary cultures were grown for two weeks in medium made hyperosmotic with additional NaCl. At the time the cells were harvested (four weeks in culture), the medium osmolality of experimental cultures was approximately 600 mOsm. Amino acid, protein, and potassium contents and the cell volume were measured. Compared to cells maintained in control medium (approximately 300 mOsm), cells grown in hyperosmotic conditions had over two times the content of taurine and five times the content of glutamine. Alanine, aspartate, glutamate, glycine, and tyrosine contents also were elevated in these hyperosmotic-treated cells, while asparagine contents were unchanged relative to control cells. Cell volume and potassium content were decreased to approximately 50% of control levels by the hyperosmotic treatment while total protein content per cell was unchanged relative to cells from control cultures. Seven min after hyperosmotic-exposed cells were rapidly diluted into PBS with osmolality equal to about 330 mOsm, cell contents of alanine, asparagine, glutamine, glutamate, glycine, taurine, and tyrosine fell toward control levels. The data indicate that significant alterations in intracellular osmolytes occur in astrocytes adapted to hyperosmotic conditions. We suggest that a loss of intracellular potassium is at least partially compensated by accumulation of taurine, glutamine, and perhaps other amino acids acting as intracellular osmolytes.