UPTAKE OF [N-ME-H-3]-LABELED CHOLINE BY SYNAPTOSOMES FROM THE CENTRAL NERVOUS-SYSTEM OF LOCUSTA-MIGRATORIA

The accumulation of 3H-choline by isolated synaptosomes from the CNS of locust was studied at concentrations varying from 0.05-40 .mu.M. Kinetic analysis of the saturable process revealed a high-affinity and a low-affinity system. The high-affinity uptake was competitively inhibited by hemicholinium-3 and was absolutely dependent on external Na. Elevated K concentrations inhibited choline uptake. The choline uptake by insect synaptosomes was remarkably resistant to a variety of metabolic inhibitors. The reduced choline uptake under depolarizing conditions (high K concentration or veratridine) in the absence of Ca implies that electrochemical gradients are important for high-affinity choline uptake. Depolarization of preloaded synaptosomes under appropriate conditions resulted in a significant release of newly accumulated choline radioactivity.