Involvement of Na+-K+ pump in L-glutamate clearance by cultured rat cortical astrocytes.

When L-glutamate (150 microM) was added to rat cortical astrocyte cultures and incubated for 1-3 h, the extracellular L-glutamate concentration declined with time. The time-dependent decline of extracellular L-glutamate concentration was due to the uptake of L-glutamate by astrocytes. The clearance of extracellular L-glutamate by astrocytes was partly slowed down by replacing NaCl with choline chloride or LiCl in the extracellular medium or by adding KCI, and was completely blocked by replacing NaCl with KCI. Furthermore, the L-glutamate clearance was blocked by Na+-K+ pump inhibitors, ouabain and vanadate, but was not affected by Na+ channel modulators nor by K+ channel blockers. These results suggest that the clearance of extracellular L-glutamate by astrocytes is dependent on both Na+ and K+ gradients across the plasma membrane, and that the Na+-K+ pump plays a role in the regulation of L-glutamate clearance.