The naturally occurring toxin rottlerin has been used by other laboratories as a specific inhibitor of protein kinase C-delta (PKC-d) to obtain evidence that the activitydependent distribution of glutamate transporter GLAST is regulated by PKC-d mediated phosphorylation. Using immunofluorescence labelling for GLAST and deconvolution microscopy we have observed that D-aspartateinduced redistribution of GLAST towards the plasma membranes of cultured astrocytes was abolished by rottlerin. In brain tissue in vitro, rottlerin reduced apparent activity of (Na?, K?)-dependent ATPase (Na?, K?-ATPase) and increased oxygen consumption in accordance with its known activity as an uncoupler of oxidative phosphorylation (‘‘metabolic poison’’). Rottlerin also inhibited Na?, K?-ATPase in cultured astrocytes. As the glutamate transport critically depends on energy metabolism and on the activity of Na?, K?-ATPase in particular, we suggest that the metabolic toxicity of rottlerin and/or the decreased activity of the Na?, K?-ATPase could explain both the glutamate transport inhibition and altered GLAST distribution caused by rottlerin even without any involvement of PKC-d-catalysed phosphorylation in the process.