Resolution of monoamine uptake into binding and translocation components.

Kinetic analysis of the energy-independent accumulation of noradrenaline as determined by either sodium omission or osmotic lysis, revealed two components: a) a low affinity system which may represent extraneuronal uptake and b) a high affinity component which was characteristic of the physiological re-uptake process. A comparison between intact and lysed synaptosomes suggested that this high affinity system may represent binding to the carrier protein which was no dependent on external sodium. Qualitatively similar results were observed for serotonin. The results are discussed in relation to models of neuronal re-uptake.