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The Journal of Neuroscience, November 22, 2006, 26(47):12283-12293; doi:10.1523/JNEUROSCI.2665-06.2006
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Cellular/Molecular
Ca2+ Dynamics along Identified Synaptic Terminals in Drosophila Larvae
Gregory A. Lnenicka,
Jeffrey Grizzaffi,
Bomi Lee, and
Nidhi Rumpal
Department of Biological Sciences, University at Albany, State University of New York, Albany, New York 12222
Correspondence should be addressed to Gregory A. Lnenicka, Department of Biological Sciences, University at Albany, State University of New York, Albany, NY 12222. Email: gregl{at}albany.edu
Changes in intracellular Ca2+ concentration ([Ca2+]i) play an important role in the function and plasticity of synapses. We characterized the changes in [Ca2+]i produced by action potentials (APs) along two identified motor terminals found on separate muscle fibers in Drosophila larvae and examined factors that influence the amplitude and duration of the residual Ca2+ signal. We were able to measure Ca2+ transients produced along terminals by both single APs and AP trains using Oregon Green 488 BAPTA-1 and streaming images at 2050 Hz. The decay of [Ca2+]i after single APs or AP trains was well fit by a single exponential. For single APs, the Ca2+ transient amplitude and decay rate were similar at boutons and bottleneck regions and much smaller at the axon. Also, the amplitude of single-AP Ca2+ transients was inversely correlated with bouton width. During AP trains, the increase in [Ca2+]i became more uniform: the difference in boutons and axons was reduced, and the increase in [Ca2+]i was not correlated with bouton width. The [Ca2+]i decay was directly correlated with bouton width for both single APs and AP trains. For one terminal, distal boutons had larger single-AP Ca2+ transients than proximal ones, probably attributable to greater Ca2+ influx for distal boutons. Pharmacological studies showed that Ca2+ clearance from these synaptic terminals after single APs and AP trains was primarily attributable to Ca2+ extrusion by the plasma membrane Ca2+ ATPase (PMCA). Immunostaining of larval muscle fibers showed high levels of the PMCA at the neuromuscular junction.
Key words: Drosophila; pump; Ca2+; synapse; neuromuscular junction; axon terminal
Received June 23, 2006;
revised Oct. 18, 2006;
accepted Oct. 19, 2006.
Correspondence should be addressed to Gregory A. Lnenicka, Department of Biological Sciences, University at Albany, State University of New York, Albany, NY 12222. Email: gregl{at}albany.edu
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