Choline: High-Affinity Uptake by Rat Brain Synaptosomes

Abstract

Synaptosomes from rat brain accumulate choline by two kinetically distinct processes, a high-affinity uptake system [Michaelis constant (K_m) = 1 x 10^-6M], and a low-affinity system (K_m = 9 x 10^-5M). The high-affinity uptake system requires sodium, and is associated with considerable formation of acetylcholine. The low-affinity uptake system is less dependent on sodium, and does not appear to be associated with a marked degree of acetylcholine formation. The high-affinity choline uptake appears to represent selective choline accumulation by cholinergic neurons.