Glutamate Uptake Stimulates Na+,K+‐ATPase Activity in Astrocytes via Activation of a Distinct Subunit Highly Sensitive to Ouabain

Abstract: The excitatory amino acid glutamate was previously shown to stimulate aerobic glycolysis in astrocytes by a mechanism involving its uptake through an Na+‐dependent transporter. Evidence had been provided that Na+,K+‐ATPase might be involved in this process. We have now measured the activity of Na+,K+‐ATPase in cultured astrocytes, using ouabain‐sensitive 86Rb uptake as an index. l‐Glutamate increases glial Na+,K+‐ATPase activity in a concentration‐dependent manner with an EC50 = 67 µM. Both l‐ and d‐aspartate, but not d‐glutamate, produce a similar response, an observation that is consistent with an uptake‐related effect rather than a receptor‐mediated one. Under basal conditions, concentration‐dependent inhibition of Na+,K+‐ATPase activity in astrocytes by ouabain indicates the presence of a single catalytic site with a low affinity for ouabain (K0.5 = 113 µM), compatible with the presence of an α1 isozyme. On stimulation with glutamate, however, most of the increased activity is inhibited by low concentrations of ouabain (K0.5 = 20 nM), thus revealing a high‐affinity site akin to the α2 isozyme. These results suggest that astrocytes possess a glutamate‐sensitive isoform of Na+,K+‐ATPase that can be mobilized in response to increased neuronal activity.