Changes of the membrane potential in striatal synaptoneurosome, synaptosome and membrane sac preparations induced by glutamate, kainate and aspartate as measured with a cyanine dye DiS-C 2-(5)

Abstract

The effects of glutamate, kainate and aspartate on the membrane potential of striatal synaptoneurosome, synaptosome and membrane sac preparations were studied by using a potential sensitive cyanine dye DiS-C 2-(5). Excitatory amino acids glutamate and aspartate had a depolarizing effect on synaptoneurosomes, 7.9 μM glutamate and 2.8 μM aspartate produced a half-maximal response. Depolarizations induced by glutamate and aspartate were dependent on the concentration of extracellular sodium ions, a maximal response occurred at around 40 mM of external Na +. Kainate induced a dual effect on synaptoneurosomes. In a standard Na +-based medium a hyperpolarization, likely due to inhibition of a presynaptic sodium-dependent glutamate uptake, predominated over a postsynaptic kainate receptor-mediated depolarization that was observed when electrogenic glutamate uptake was inhibited. This interpretation was supported by results obtained with synaptosome and membrane sac preparations. In a standard Na +-based medium kainate had a hyperpolarizing effect on synaptosomes while in the membrane sac preparation kainate induced a depolarization.