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The Journal of Neuroscience, December 15, 2000, 20(24):9059-9070
Origin Sites of Calcium Release and Calcium Oscillations in Frog
Sympathetic Neurons
Stefan I.
McDonough,
Zoltán
Cseresnyés, and
Martin F.
Schneider
Department of Biochemistry and Molecular Biology, University of
Maryland Medical School, Baltimore, Maryland 21201
In many neurons, Ca2+ signaling depends on
efflux of Ca2+ from intracellular stores into the
cytoplasm via caffeine-sensitive ryanodine receptors (RyRs) of the
endoplasmic reticulum. We have used high-speed confocal microscopy to
image depolarization- and caffeine-evoked increases in cytoplasmic
Ca2+ levels in individual cultured frog sympathetic
neurons. Although caffeine-evoked Ca2+ wave fronts
propagated throughout the cell, in most cells the initial
Ca2+ release was from one or more discrete sites
that were several micrometers wide and located at the cell edge, even
in Ca2+-free external solution. During cell-wide
cytoplasmic [Ca2+] oscillations triggered by
continual caffeine application, the initial Ca2+
release that began each Ca2+ peak was from the same
subcellular site or sites. The Ca2+ wave fronts
propagated with constant amplitude; the spread was mostly via
calcium-induced calcium release. Propagation was faster around
the cell periphery than radially inward. Local Ca2+
levels within the cell body could increase or decrease independently of
neighboring regions, suggesting independent action of spatially separate Ca2+ stores. Confocal imaging of
fluorescent analogs of ryanodine and thapsigargin, and of MitoTracker,
showed potential structural correlates to the patterns of
Ca2+ release and propagation. High densities of RyRs
were found in a ring around the cell periphery, mitochondria in a
broader ring just inside the RyRs, and sarco-endoplasmic reticulum
Ca2+ ATPase pumps in hot spots at the cell edge.
Discrete sites at the cell edge primed to release
Ca2+ from intracellular stores might preferentially
convert Ca2+ influx through a local area of plasma
membrane into a cell-wide Ca2+ increase.
Key words:
ryanodine receptor; sympathetic neuron; caffeine; confocal microscopy; calcium; calcium wave; calcium oscillations; calcium-induced calcium release; subsurface cistern; fluo-4
Copyright © 2000 Society for Neuroscience 0270-6474/00/20249059-12$05.00/0
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