Biochemical and Biophysical Aspects of Stimulation Induced Vesicle Heterogeneity in Cholinergic Synaptic Vesicles

Abstract

In a series of previous experiments we provided evidence that on stimulation-induced transmitter release synaptic vesicles in the cholinergic nerve terminals of the Torpedo electric organ start to undergo cycles of exo- and endocytosis. The recycled vesicles can be shown to contain extracellular marker of high molecular weight if it has been applied in high concentrations (1). They are smaller and also denser and thus can be separated from vesicles which have not yet released their stores of transmitter. If radiolabelled precursors are applied the recycled vesicles contain both ACh (9) and ATP (13) of high specific radioactivity. The evidence for this is derived from density gradient centrifugation studies using sucrose gradients in a zonal rotor and from related electron microscopical investigations.