Presynaptic pH and vesicle fusion in Drosophila larvae neurones
Version of Record online: 3 JUN 2013
Copyright © The Authors Synapse Published by Wiley Periodicals, Inc.
This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.
Volume 67, Issue 11, pages 729–740, November 2013
How to Cite
Caldwell, L., Harries, P., Sydlik, S. and Schwiening, C. J. (2013), Presynaptic pH and vesicle fusion in Drosophila larvae neurones. Synapse, 67: 729–740. doi: 10.1002/syn.21678
- Issue online: 17 SEP 2013
- Version of Record online: 3 JUN 2013
- Accepted manuscript online: 7 MAY 2013 03:46AM EST
- Manuscript Accepted: 22 APR 2013
- Manuscript Received: 29 JAN 2013
- Wellcome Trust
- Amgen Scholars Program
- neuromuscular junction;
- intracellular pH;
- Na+/H+ exchanger;
- synaptic transmission
Both intracellular pH (pHi) and synaptic cleft pH change during neuronal activity yet little is known about how these pH shifts might affect synaptic transmission by influencing vesicle fusion. To address this we imaged pH- and Ca2+-sensitive fluorescent indicators (HPTS, Oregon green) in boutons at neuromuscular junctions. Electrical stimulation of motor nerves evoked presynaptic Ca2+i rises and pHi falls (∼0.1 pH units) followed by recovery of both Ca2+i and pHi. The plasma-membrane calcium ATPase (PMCA) inhibitor, 5(6)-carboxyeosin diacetate, slowed both the calcium recovery and the acidification. To investigate a possible calcium-independent role for the pHi shifts in modulating vesicle fusion we recorded post-synaptic miniature end-plate potential (mEPP) and current (mEPC) frequency in Ca2+-free solution. Acidification by propionate superfusion, NH4+ withdrawal, or the inhibition of acid extrusion on the Na+/H+ exchanger (NHE) induced a rise in miniature frequency. Furthermore, the inhibition of acid extrusion enhanced the rise induced by propionate addition and NH4+ removal. In the presence of NH4+, 10 out of 23 cells showed, after a delay, one or more rises in miniature frequency. These findings suggest that Ca2+-dependent pHi shifts, caused by the PMCA and regulated by NHE, may stimulate vesicle release. Furthermore, in the presence of membrane permeant buffers, exocytosed acid or its equivalents may enhance release through positive feedback. This hitherto neglected pH signalling, and the potential feedback role of vesicular acid, could explain some important neuronal excitability changes associated with altered pH and its buffering. Synapse 67:729–740, 2013. © 2013 Wiley Periodicals, Inc.