Glial Glutamate Transporters: Electrophysiology

An intuitively obvious requirement for chemical neurotransmission is prompt removal of neurotransmitter following synaptic release. This is necessary for terminating the actions of the transmitter on the postsynaptic cell, and it is also important for controlling heterosynaptic spillover in order to maintain synapse specificity. In the case of glutamate, the principal excitatory neurotransmitter in the nervous system of vertebrates, it is also important to tightly control ambient extracellular transmitter levels in order to prevent excitotoxic damage from excessive receptor activity. This task is chiefly accomplished through reuptake mediated by excitatory amino acid transporters found on the plasma membranes of glia and neurons in the central nervous system (CNS). This article focuses on the electrophysiology of glial glutamate transporters and highlights some of the key aspects of the structure, mechanisms, and roles in synaptic transmission of these molecules. While the vast majority of glutamate transport activity in mammalian CNS is associated with glial cells, many of the glial transporter properties discussed here are shared with glutamate transporters found on neurons.