Transmembrane Potential and Cation Diffusion Gradients in Isolated Cholinergic Synaptic Vesicles: Possible Model for Energization of Vesicular Acetylcholine Uptake
Recent experiments with Torpedo electroplaque synapses lend support for the idea that in activated terminals synaptic vesicles are mobilized into a pool of active vesicles which may undergo several cycles of acetylcholine (ACh) release and reuptake (4,5,7). The active but not the unmobilized depot vesicles become highly charged with the newly synthesized ACh, suggesting that the exocytotic event somehow energizes these vesicles for subsequent uptake of ACh from cytoplasm. A clue to the possible nature of this process was provided by the observation that gramicidin induces an electrogenic influx of choline (Ch) or ACh into isolated vesicles (1). This communication presents some experimental evidence consistent with the hypothesis that the exocytotic release of ACh and the concomitant imposition of ∆Na+ across the vesicle membrane due to a rapid equilibration between the intravesicular and extracellular medium may be a precondition for energization of ACh uptake into vesicles.
KeywordsSynaptic Vesicle Vesicle Membrane Steady State Distribution Subsequent Uptake Minute Figure
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- 1.Carpenter, R.S. and Parsons, S.M. (1978): J. Biol. Chem. 253:326–329.Google Scholar