Depolarization of cultured astrocytes by glutamate and aspartate

Abstract

The excitatory transmitter substances glutamate and aspartate are known to have a depolarizing action on cultured CNS neurones, the depolarization being associated with an increase in membrane conductance. When the effects of these amino acids (at a concentration of 10 −4 M) were studied on the membrane potential and resistance of cultured glial cells, they also caused a depolarization of many astrocytes but without producing significant changes in membrane resistance. The majority of glial cells depolarized by glutamate and aspartate were lying in the vicinity of neurones in the dense zone of the cultures, whereas isolated astrocytes in the outgrowth zone were usually not affected by the amino acids. 4-Aminopyridine (5 mM), a substance known to block K +-conductance in various excitable membranes, reversibly reduced or abolished the depolarization caused by glutamate and aspartate on glial cells, but had no or only a small effect on the depolarization of neurones caused by these amino acids. These results suggest that the depolarization of glial cells by glutamate and aspartate is caused by an increase in the concentration of extracellular K + which is released from neighbouring neurones during their activation by the amino acids.