GLUTAMATE UPTAKE STIMULATES NA-ATPASE ACTIVITY IN ASTROCYTES VIA ACTIVATION OF A DISTINCT SUBUNIT HIGHLY SENSITIVE TO OUABAIN(,K+)

The excitatory amino acid glutamate was previously shown to stimulate aerobic glycolysis in astrocytes by a mechanism involving its uptake t hrough an Na+-dependent transporter. Evidence had been provided that N a+,K+-ATPase might be involved in this process. We have now measured t he activity of Na+,K+-ATPase in cultured astrocytes, using ouabain-sen sitive Rb-86 uptake as an index. L-Glutamate increases glial Na+,K+-AT Pase activity in a concentration-dependent manner with an EC50 = 67 mu M. Both L- and D-aspartate, but not D-glutamate, produce a similar re sponse, an observation that is consistent with an uptake-related effec t rather than a receptor-mediated one. Under basal conditions, concent ration-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 (K-0.5 = 113 mu M), compatible with the presence of an alpha(1) isozyme. On stimulation with glutamate, however, most o f the increased activity is inhibited by low concentrations of ouabain (K-0.5 = 20 nM), thus revealing a high-affinity site akin to the alph a(2) isozyme. These results suggest that astrocytes possess a glutamat e-sensitive isoform of Na+,K+-ATPase that can be mobilized in response to increased neuronal activity.