Uptake and release of norepinephrine by rat brain tissue fractions prepared by ultrafiltration

Abstract— Isolated nerve endings were removed from crude homogenates of rat brain by Millipore filters of pore size 0-5-0-8 μm. Synaptosomes containing L-[³H]norepinephrine were incompletely removed from a non-ionic medium by 0-8 μm pore filters, but were nearly quantitatively removed from Krebs’medium, as demonstrated by density gradient subcellular distribution. In suspension, synaptosomes accumulated labelled norepinephrine. Catecholamine uptake was active; it was inhibited by ouabain, imipramine, cocaine, β-phenethylamine and amantadine. Bound norepinephrine was released by a high concentration of K⁺. Nerve endings trapped on ultrafilters behaved very similarly to synaptosomes suspended in Krebs’medium by actively accumulating norepinephrine and serotonin; they also possessed monoamine oxidase activity and norepinephrine was released from them by increased concentrations of K⁺. Ultrafiltration provides a simple, rapid method of preparing metabolically active synaptosomes.