Critical assessment of noradrenaline uptake in synaptosomal preparations

Synaptosomes and other subcellular organelles were prepared from rat brain using a vertical rotor. The preparation time was reduced by up to 60% compared to conventional techniques. Uptake of [3H]-(−)-noradrenaline into subcellular fractions was characterised. The characteristics of this uptake were dependent on the subcellular composition and anatomical origin. Various methods of correction for energy independent processes were compared, but only sodium ion removal from the medium selectively inhibited the energy dependent uptake mechanism. Kinetic analysis of data revealed that high and low affinity uptake systems existed. The relative contributions of these systems were dependent on the fraction under analysis. Noradrenaline uptake was not exclusively localised in noradrenergic terminals. Selective inhibitors of the noradrenaline uptake process (tricyclic antidepressants) inhibited energy dependent uptake completely only in purified synaptosomes prepared from cortex. In whole brain synaptosomal fractions, noradrenaline was partially accumulated into dopaminergic neurones; this uptake process was not inhibited by tricyclic antidepressants.