KCl movements during potassium-induced cytotoxic swelling of cultured astrocytes

Astrocytes in primary cultures from mouse cortex were used to investigate the ionic mechanism of cytotoxic swelling which develops after exposure of the cells to 60 mM K+ under isosmotic conditions. Radiotracer analysis combined with a washing efflux method were used to analyze ion changes. We found that both the K+ and the Cl- content increased by about 100% within 1 min after increasing the external K+, and remained constant for 30 min thereafter. The mechanisms, i.e., Na+,K+-ATPase-mediated transport and NaCl/KCl contransport, that are involved in glial ion homeostasis in physiologic situations (extracellular K+ increase to 12 mM) are disturbed in this system and do not contribute to the cytotoxic swelling induced by pathologic K+ concentrations. The Na+,K+-ATPase-mediated K+ uptake is not additionally stimulated by the pathologic K+ increase. The NaCl/KCl cotransport was minimal, presumably due to a severe reduction of the Na+ driving force by the depolarization. The mechanisms of this pathological swelling were found to consist mainly of a passive KCl influx. This influx is mediated by a disturbance of the Donnan equilibrium. It probably involves an increase of the Cl- permeability by activation of a previously described voltage-dependent Cl- channel, which is closed under physiological conditions. However, it was found that the intracellular Cl- accumulation did not completely match the corresponding K+ accumulation. Possible reasons for this anion deficit are discussed.