GABA and glycine receptors in CNS cultures: autoradiographic binding and electrophysiological studies

Autoradiographic studies have shown that GABA, glycine and their antagonists bicuculline and strychnine are bound to many cultured neurones but not to glial cells. The hyperpolarization of GABA and glycine on CNS neurones is associated with an increase in membrane conductance, whereas the depolarization of glial cells by these amino acids is not accompanied by a change in membrane resistance. Using K+-sensitive electrodes, it was observed that the glial depolarization correlates well with the increase of the extracellular K+-concentration. 4-AP which blocks K+-conductance of excitable cells reversibly abolished both the glial depolarization and the increase of extracellular K+-concentration caused by GABA and glycine. It is concluded that, unlike neurones, glial cells may not possess receptors for GABA and glycine and that the depolarization by these amino acids is an indirect effect caused by an increase of extracellular K+ released from adjacent neurones.