Glutamate uptake stimulates Na+,K+-ATPase activity in astrocytes via activation of a distinct subunit highly sensitive to ouabain.
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 microM. 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 microM), compatible with the presence of an alpha1 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 alpha2 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.
Pellerin
L
L
Laboratoire de Recherche Neurologique, Institut de Physiologie et Service de Neurologie du CHUV, Faculté de Médecine, Université de Lausanne, Switzerland.
Magistretti
P J
PJ
D000818:Animals; D000831:Animals, Newborn; D001253:Astrocytes / Q000187:drug effects / Q000378:metabolism*; D001692:Biological Transport / Q000187:drug effects; D002478:Cells, Cultured; D002540:Cerebral Cortex / Q000378:metabolism*; D004789:Enzyme Activation; D018698:Glutamic Acid / Q000378:metabolism* / Q000494:pharmacology*; D007700:Kinetics; D046911:Macromolecular Substances; D051379:Mice; D010042:Ouabain / Q000494:pharmacology*; D012044:Regression Analysis; D012413:Rubidium / Q000493:pharmacokinetics; D000254:Sodium-Potassium-Exchanging ATPase / Q000737:chemistry / Q000187:drug effects / Q000378:metabolism*
D046911:Macromolecular Substances; D018698:Glutamic Acid; D010042:Ouabain; D000254:Sodium-Potassium-Exchanging ATPase; D012413:Rubidium