Synaptic vesicles control the time course of neurotransmitter secretion via a Ca2+/H+ antiport

• Published in: The Journal of physiology 2011-01, Vol.589 (1), p.149-167
• Main Authors: Cordeiro, J. Miguel, Gonçalves, Paula P., Dunant, Yves
• Format: Article
• Language: English
• Subjects: Acetylcholine - metabolism; Animals; Antiporters - metabolism; Calcium - metabolism; Cation Transport Proteins - metabolism; Cholinesterase Inhibitors - pharmacology; Electric Organ - drug effects; Electric Organ - metabolism; Electric Stimulation; Enzyme Inhibitors - pharmacology; Evoked Potentials; Female; Kinetics; Macrolides - pharmacology; Male; Neuroscience; Physostigmine - pharmacology; Presynaptic Terminals - drug effects; Presynaptic Terminals - metabolism; Retina; Strontium - metabolism; Synaptic Transmission - drug effects; Synaptic Vesicles - drug effects; Synaptic Vesicles - metabolism; Synaptosomes - metabolism; Torpedo; Transmitters; Vacuolar Proton-Translocating ATPases - antagonists & inhibitors; Vacuolar Proton-Translocating ATPases - metabolism; Zinc
• ISSN: 0022-3751; 1469-7793
• DOI: 10.1113/jphysiol.2010.199224

Non‐technical summary A low‐affinity Ca2+/H+ antiport has been described in the membrane of synaptic vesicles isolated from mammalian brain cortex. We show here evidence that the role of the vesicular Ca2+/H+ antiport is to shorten the time course of transmitter release during individual nerve impulses. The process seems of great importance since it can enable rapid synapses to transmit briefer signals, and so work at high frequencies. We investigated the physiological role of the vesicular Ca2+/H+ antiport in rapid synaptic transmission using the Torpedo electric organ (a modified neuromuscular system). By inhibiting V‐type H+‐transporting ATPase (V‐ATPase), bafilomycin A1 dissipates the H+ gradient of synaptic vesicles, thereby abolishing the Ca2+/H+ antiport driving force. In electrophysiology experiments, bafilomycin A1 significantly prolonged the duration of the evoked electroplaque potential. A biochemical assay for acetylcholine (ACh) release showed that the effect of bafilomycin A1 was presynaptic. Indeed, bafilomycin A1 increased the amount of radio‐labelled ACh released in response to paired‐pulse stimulation. Bafilomycin A1 also enhanced Ca2+‐dependent ACh release from isolated nerve terminals (synaptosomes). The bafilomycin‐induced electroplaque potential lengthening did not arise from cholinesterase inhibition, since eserine (which also prolonged the electroplaque potential) strongly decreased evoked ACh release. Bafilomycin A1 augmented the amount of calcium accumulating in nerve terminals following a short tetanic stimulation and delayed subsequent calcium extrusion. By reducing stimulation‐dependent calcium accumulation in synaptic vesicles, bafilomycin A1 diminished the corresponding depletion of vesicular ACh, as tested using both intact tissue and isolated synaptic vesicles. Strontium ions inhibit the vesicular Ca2+/H+ antiport, while activating transmitter release at concentrations one order of magnitude higher than Ca2+ does. In the presence of Sr2+ the time course of the electroplaque potential was also prolonged but, unlike bafilomycin A1, Sr2+ enhanced facilitation in paired‐pulse experiments. It is therefore proposed that the vesicular Ca2+/H+ antiport function is to shorten ‘phasic’ transmitter release, allowing the synapse to transmit briefer impulses and so to work at higher frequencies. A low‐affinity Ca2+/H+ antiport has been described in the membrane of synaptic vesicles isolated from mammalian brain cortex. We show here evid