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Focal Macropatch Recordings of Synaptic Currents from the Drosophila Larval Neuromuscular Junction
Published on: September 25, 2017
Ca2+ dynamics along identified synaptic terminals in Drosophila larvae
Gregory A Lnenicka1, Jeffrey Grizzaffi, Bomi Lee
1Department of Biological Sciences, University at Albany, State University of New York, Albany, New York 12222, USA. gregl@albany.edu
Summary
Changes in intracellular calcium ([Ca2+]i) influence synapse function. This study reveals how action potentials affect calcium signals in Drosophila motor terminals, identifying plasma membrane Ca2+ ATPase (PMCA) as key for calcium clearance.
Area of Science:
- Neuroscience
- Cell Biology
- Biophysics
Background:
- Intracellular calcium concentration ([Ca2+]i) dynamics are crucial for synaptic function and plasticity.
- Understanding how action potentials (APs) shape [Ca2+]i signals at motor terminals is essential for elucidating synaptic transmission mechanisms.
Purpose of the Study:
- To characterize [Ca2+]i changes in Drosophila larval motor terminals in response to single APs and AP trains.
- To investigate factors influencing the amplitude and duration of residual Ca2+ signals.
- To identify the primary mechanisms of Ca2+ clearance at these terminals.
Main Methods:
- Utilized Oregon Green 488 BAPTA-1 and high-speed imaging (20-50 Hz) to measure [Ca2+]i transients in response to APs.
- Analyzed Ca2+ transient decay kinetics, fitting data to a single exponential model.
- Performed pharmacological studies to assess Ca2+ clearance mechanisms and immunostaining to localize key proteins.
Main Results:
- Single APs elicited smaller [Ca2+]i transients at axons compared to boutons and bottleneck regions, with amplitude inversely correlated to bouton width.
- During AP trains, [Ca2+]i increases became more uniform across terminal regions and independent of bouton width.
- Ca2+ decay time constant (tau) correlated positively with bouton width for both single APs and AP trains.
- Distal boutons showed larger single-AP Ca2+ transients than proximal ones, suggesting regional differences in Ca2+ influx.
- Pharmacological inhibition indicated that plasma membrane Ca2+ ATPase (PMCA) is the primary mechanism for Ca2+ extrusion.
Conclusions:
- Synaptic terminal morphology influences [Ca2+]i dynamics, particularly for single APs.
- Ca2+ signal uniformity increases during high-frequency activity (AP trains).
- Plasma membrane Ca2+ ATPase (PMCA) plays a critical role in clearing intracellular calcium from Drosophila motor terminals, as evidenced by its localization at the neuromuscular junction.