Effects of potassium on the anion and cation contents of primary cultures of mouse astrocytes and neurons

Inastrocytes, as K⁺]_o was increased from 1.2 to 10 mM, K⁺]_i and Cl^–]_i were increased, whereas Na⁺]_i was decreased. As K⁺]_o was increased from 10 to 60 mM, intracellular concentration of these three ions showed no significant change. When K⁺]_o was increased from 60 to 122 mM, an increase in K⁺]_i and Cl^–]_i and a decrease in Na⁺]_i were observed.Inneurons, as K⁺]_o was increased from 1.2 to 2.8 mM, Na⁺]_i and Cl^–]_i were decreased, whereas K⁺]_i was increased. As K⁺]_o was increased from 2.8 to 30 mM, K⁺]_i, Na⁺]_i and Cl^–]_i showed no significant change. When K⁺]_o was increased from 30 to 122 mM, K⁺]_i and Cl^–]_i were increased, whereas Na⁺]_i was decreased. Inastrocytes, pH_i increased when K⁺]_o was increased. Inneurons, there was a biphasic change in pH_i. In lower K⁺]_o (1.2–2.8 mM) pH_i decreased as K⁺]_o increased, whereas in higher K⁺]_o (2.8–122 mM) pH_i was directly related to K⁺]_o. In bothastrocytes andneurons, changes in K⁺]_o did not affect the extracellular water content, whereas the intracellular water content increased as the K⁺]_o increased. Transmembrane potential (E_m) as measured with Tl-204 was inversely related to K⁺]_o between 1.2 and 90 mM, a ten-fold increase in K⁺]_o depolarized the astrocytes by about 56 mV and the neurons about 52 mV. The E_m values measured with Tl-204 were close to the potassium equilibrium potential (E_k) except those in neurons at lower K⁺]_o. However, they were not equal to the chloride equilibrium potential (E_Cl) at K⁺]_o lower than 30 mM in both astrocytes and neurons. Results of this study demonstrate that alteration of K⁺]_o produced different changes in K⁺]_i, Na⁺]_i, Cl^–]_i, and pH_i in astrocytes and neurons. The data show that astrocytes can adapt to alterations in K⁺]_o, in such a way to maintain a more suitable environment for neurons.