Vesicular Heterogeneity and Turnover of Acetylcholine and ATP in Cholinergic Synaptic Vesicles

Abstract

Publisher Summary This chapter discusses the vesicular heterogeneity and turnover of acetylcholine (ACh) and adenosine triphosphate (ATP) in cholinergic synaptic vesicles. This chapter uses the torpedo electric organ system to approach the problem of vesicular storage and the release of acetylcholine. In a series of morphological experiments, blocks of electric tissue was perfused with an extracellular marker (dextran) in order to study its uptake into synaptic vesicles. By using low frequency stimulation, an experimental condition was chosen that do not cause any sign of serious exhaustion of nerve terminal resources like mitochondrial swelling, in foldings of the presynaptic membrane or loss of synaptic vesicles. In order to study the turnover of the vesicle constituents, ACh and ATP, radiolabelled precursors were applied to the perfusate, and vesicular uptake was investigated with and without low frequency stimulation. Vesicles were isolated on zonal sucrose gradients, which had a high density resolution in the range of synaptic vesicle buoyant density. A third approach uses the double labelling of synaptic vesicles with the real and a false transmitter. In experiments with [ 3 H]pyrrolcholine as a false precursor together with [ 14 C] choline it could shown that acetylpyrrolcholine and acetylcholine are released from cholinergic nerve terminals in the same ratio as they are lost from synaptic vesicles on stimulation.