High‐Affinity Uptake of [3H]Norepinephrine by Primary Astrocyte Cultures and Its Inhibition by Tricyclic Antidepressants

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Abstract
Primary astrocyte cultures from neonatal rat brains show uptake of [3H]norepinephrine ([3H]NE). This uptake has a high-affinity component with an apparent Km of approximately 3 × 10−7 M. At 10−7 M [3H]NE both the initial rate of uptake and steady-state content of [3H]NE is inhibited by up to 95% by omission of external Na+. The Na+-dependent component of this uptake is totally inhibited by the tricyclic antidepressants desipramine (DMI) and amitryptyline with IC50 values of 2 × 10−9 and 4 × 10−8 M, respectively. Inhibition of [3H]NE uptake by DMI shows competitive kinetics. These characteristics are essentially identical to those found for high-affinity uptake of NE in total membrane or synaptosome fractions from rodent brains and suggests that such uptake in neural tissue is not exclusively neuronal.