Endothelin-1 decreases glutamate uptake in primary cultured rat astrocytes

Endothelin-1 (ET-1) is a potent vasoconstrictor peptide that is also known to induce a wide spectrum of biological responses in nonvascular tissue. In this study, we found that ET-1 (100 nM) inhibited the glutamate uptake in cultured astrocytes expressing the glutamate/aspartate transporter (GLAST); astrocytes did not express the glutamate transporter-1 (GLT-1). The V-max and the K-m of the glutamate uptake were reduced by 57% and 47%, respective ly. Application of the ETA and ETB receptor antagonists BQ-123 and BQ-788 p artly inhibited the ET-1-evoked decrease in the glutamate uptake, whereas t he nonspecific ET receptor antagonist bosentan completely inhibited this de crease. Incubation of the cultures with pertussis toxin abolished the effec t of ET-1 on the uptake. The ET-1-induced decrease in the glutamate uptake was independent of extracellular free Ca2+ concentration, whereas the intra cellular Ca2+ antagonists thapsigargin and 3,4,5-trimethoxybenzoic acid 8-( diethylamino) octyl ester abolished the effect of ET-1 on the glutamate upt ake. Incubation with the protein kinase C (PKC) antagonist staurosporine, b ut not with the fatty acid-binding protein bovine serum albumin, prevented the ET-1-induced decrease in the glutamate uptake. These results suggest th at ET-1 impairs the high-affinity glutamate uptake in cultured astrocytes t hrough a G protein-coupled mechanism, involving PKC and changes in intracel lular Ca2+.