A microdialysis study in rat brain of dihydrokainate, a glutamate uptake inhibitor

Microdialysis in neostriatum of anaesthetized rats was performed to study effects on amino acid efflux of the glutamate uptake-inhibitor dihydrokainate (DHK). Both basal and K+-evoked (100 mM) efflux of glutamate increased in the presence of DHK. The increase in the basal glutamate efflux occurred at lower DHK concentrations than during K+-depolarization (when the extracellular glutamate concentration was several-fold higher), confirming that DHK is a competitive inhibitor. The increase in basal efflux caused by DHK did not exhibit Ca2+-dependency, whereas similar to 50% of the increase in glutamate efflux during K+-depolarization was Ca2+-dependent. The Ca2+-dependent efflux is related to transmitter release, whereas the Ca2+-independent efflux is probably due to metabolic events and/or transport of DHK into cells in exchange for glutamate. Taurine efflux in response to DHK increased both during basal conditions and K+-depolarization, probably secondary to the increase in glutamate concentration, whereas aspartate, GABA, glutamine and alanine effluxes did not change.