Kainic acid evokes a potassium efflux from astrocytes

Cultured astrocytes are depolarized by excitatory amino acids such as kainic acid. In these experiments we tested the hypothesis that the kainic acid-induced depolarization also causes an efflux of K+ from astrocytes in the rat. Using K+-sensitive microelectrodes we measured a K+ efflux from cultured astrocytes during the perfusion of kainic acid. The effects of kainic acid were then tested on glial cells in the neuron-free CA3 region of kainic acid-lesioned hippocampus. Glial cells were depolarized by kainic acid and an efflux of K+ was recorded. These effects are most likely due to direct effects on the glial cells because histological examination of the hippocampus showed this area to be free of neurons. Therefore it is hypothesized that kainic acid and any transmitter that depolarizes glial cells, will increase neuronal excitability indirectly by a K+ efflux from glial cells. This will have widespread implications for iontophoretic studies of transmitter actions.