Relationship between membrane potential and external potassium in human glioblastoma cells in tissue culture

Cells from a human glioblastoma (TC 526) maintained in tissue culture for ten years had a mean membrane potential of 27 ± 0.9 mV at an external potassium concentration [K 0 ] of 5.3 mM. When [K 0 ] was varied between 2.5 and 5.3 mM, membrane potential changes were close to those predicted by the Nernst equation. At higher [K 0 ], the Nernstian slope was approached only in the presence of 10 −5 M ouabain, which did not affect membrane potential at a [K 0 ] of 5.3 mM. An electrogenic sodium pump activated by high [K 0 ] could explain these findings; such a mechanism has been demonstrated in other tissues.