Poster Sessions CP07: Ions, Channels, Pumps and Transporters. Functional relationship between Na/K‐pump and glutamate receptors in cerebellum granule cells

Abstract

Stationary level of reactive oxygen species (ROS) in cerebellum granule cells of 12‐day‐old‐rats was measured using three fluorescent dyes characteristic of different location within the neuronal cell: BODIPY 581/591 (for LOO.radicals), DCF‐DA (for H202) and DHR123 (OH‐radicals in mitochondria). When the neurons were activated by N‐methyl‐d‐aspartate (NMDA) a dose‐ and time‐dependent rise of the fluorescent signal was registered with each of the three dyes; the former dye provided the smallest and the latter the largest response. 3‐HPG, a ligand for metabotropic receptors decreases ROS fluorescence and suppressed the NMDA‐induced effect. NMDA and kainic acid presented simultaneously cumulatively increased ROS levels. Ouabain, specific inhibitors of Na/K‐pump induced a considerable increase in ROS fluorescence, which was decreased by 2.5–5 mm KCl, 50 mkM Vanadate or 10 mkM D‐AP5, an inhibitor of NMDA‐activated ionic channels. The K0.5 for activation of ROS generation by Ouabain was more than 250 mkM, which is much higher than that for inhibition of Na/K‐ATPase or its rubidium pumping activity. The data show that the Na/K‐pump protein regulates ROS production by NMDA‐receptors and that the E1(Na) conformation of the Na/K‐pump being less sensitive to ouabain may be responsible for the effects. The data illustrate functional interaction between ionotropic and metabotropic receptors and Na/K‐ATPase.Acknowledgements: Supported by DAAD, Grant 325‐sm, Germany.