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Origin and modulation of action potential evoked calcium signals in hippocampal CA1 pyramidal neurons Sandler, Vladislav Michael
Abstract
Calcium is an important second messenger that participates in triggering and regulating numerous neuronal processes. Action potentials (APs or AP) initiate rapid changes of intracellular Ca2+-concentration ([Ca2+];) in both soma and dendrites of central neurons. We addressed two major questions about the origin and modulation of these changes in [Ca2 +]i. Firstly, how does a neurotransmitter, serotonin (5-HT), modulate the backpropagation of APs and associated changes in the [Ca2+]; in CA1 hippocampal pyramidal neurons? Secondly, do APs trigger Ca2+-induced Ca2+-release (CICR) from internal stores in these neurons? We used whole-cell somatic or dendritic patch-clamp recordings combined with high-speed imaging of [Ca2+]; and analyses of the responses to applications of pharmacological agents, studying the changes in electrical membrane properties and [Ca2+]i. The experiments were conducted in the CA1 pyramidal neurons of in vitro slices from the rat hippocampus (11 day- to 5 week-old). Changes in [Ca2+]; were measured in neurons filled with bisfura- 2, Calcium Green-1 or fura-2-AM. Bath applications of 5-HT increased membrane conductance and hyperpolarized both soma and apical dendrites. They also lowered peak potentials of antidromically-activated, backpropagating APs in the dendrites. In the soma, 5-HT applications increased the absolute AP-amplitude while slightly decreasing peak potentials. 5-HT reduced the amplitude of the AP-evoked changes in [Ca2+]i at all locations along the apical dendrites and soma. The application of 5-HT and antidromically evoked APs generated, through synergistic actions, increases in [Ca2+]j that propagated along dendrites (Ca2 + waves). Such waves originated in the proximal or middle apical dendrites and were not accompanied by a significant change in somatic membrane potential. A minimum of five APs was required to evoke the waves. According to these new observations and supporting literature, the waves are a likely consequence of Ca2+-induced Ca2+-release (CICR) from internal stores through (inositol-1,4,5- triphosphate) IP3-sensitive channels. In the absence of 5-HT, APs evoked CICR. Caffeine application increased the amplitude of AP-induced changes in [Ca2+]i. During simultaneous calcium imaging, the whole-cell recordings showed that caffeine application did not significantly change either the resting membrane potential or amplitude and shape of APs. The enhancement of AP-evoked Ca2+-transients due to caffeine application could not be attributed to protein phosphorylation or modulation of high-threshold Ca2+-channels. Applications of IBMX, a non-specific inhibitor of phosphodiesterases, forskolin, an activator of adenylyl cyclase, H-89, an inhibitor of PKA and PKG, or nifedipine, a blocker of high-threshold Ca2 + channels, did not mimic or prevent the caffeine effect. Pretreatment of neurons with thapsigargin or cyclopiazonic acid (CPA) -- substances that facilitate depletion of intracellular Ca2+-stores by blocking endoplasmic reticulum specific Ca2+-ATPases -- precluded this effect. Similar pretreatment with ryanodine, a blocker of 'ryanodine-sensitive' channels, also precluded the caffeine effect. Despite a presence or absence of caffeine, applications of thapsigargin, ryanodine or CPA reduced the AP-evoked changes in [Ca2+]i. From these new experimental observations, we can conclude that the CICR through ryanodine-sensitive channels contributes to the AP-induced changes of [Ca2+]; in hippocampal CA1 pyramidal neurons. [Scientific formulae used in this abstract could not be reproduced.]
Item Metadata
Title |
Origin and modulation of action potential evoked calcium signals in hippocampal CA1 pyramidal neurons
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Creator | |
Publisher |
University of British Columbia
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Date Issued |
1999
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Description |
Calcium is an important second messenger that participates in
triggering and regulating numerous neuronal processes. Action potentials
(APs or AP) initiate rapid changes of intracellular Ca2+-concentration ([Ca2+];)
in both soma and dendrites of central neurons. We addressed two major
questions about the origin and modulation of these changes in [Ca2 +]i. Firstly,
how does a neurotransmitter, serotonin (5-HT), modulate the
backpropagation of APs and associated changes in the [Ca2+]; in CA1
hippocampal pyramidal neurons? Secondly, do APs trigger Ca2+-induced
Ca2+-release (CICR) from internal stores in these neurons?
We used whole-cell somatic or dendritic patch-clamp recordings
combined with high-speed imaging of [Ca2+]; and analyses of the responses to
applications of pharmacological agents, studying the changes in electrical
membrane properties and [Ca2+]i. The experiments were conducted in the
CA1 pyramidal neurons of in vitro slices from the rat hippocampus (11 day- to
5 week-old). Changes in [Ca2+]; were measured in neurons filled with bisfura-
2, Calcium Green-1 or fura-2-AM.
Bath applications of 5-HT increased membrane conductance and
hyperpolarized both soma and apical dendrites. They also lowered peak
potentials of antidromically-activated, backpropagating APs in the dendrites.
In the soma, 5-HT applications increased the absolute AP-amplitude while
slightly decreasing peak potentials. 5-HT reduced the amplitude of the AP-evoked
changes in [Ca2+]i at all locations along the apical dendrites and soma.
The application of 5-HT and antidromically evoked APs generated,
through synergistic actions, increases in [Ca2+]j that propagated along dendrites
(Ca2 + waves). Such waves originated in the proximal or middle apical dendrites
and were not accompanied by a significant change in somatic membrane potential.
A minimum of five APs was required to evoke the waves. According to these
new observations and supporting literature, the waves are a likely consequence of
Ca2+-induced Ca2+-release (CICR) from internal stores through (inositol-1,4,5-
triphosphate) IP3-sensitive channels.
In the absence of 5-HT, APs evoked CICR. Caffeine application
increased the amplitude of AP-induced changes in [Ca2+]i. During
simultaneous calcium imaging, the whole-cell recordings showed that caffeine
application did not significantly change either the resting membrane potential
or amplitude and shape of APs. The enhancement of AP-evoked Ca2+-transients due to caffeine application could not be attributed to protein
phosphorylation or modulation of high-threshold Ca2+-channels. Applications
of IBMX, a non-specific inhibitor of phosphodiesterases, forskolin, an
activator of adenylyl cyclase, H-89, an inhibitor of PKA and PKG, or
nifedipine, a blocker of high-threshold Ca2 + channels, did not mimic or
prevent the caffeine effect. Pretreatment of neurons with thapsigargin or
cyclopiazonic acid (CPA) -- substances that facilitate depletion of intracellular
Ca2+-stores by blocking endoplasmic reticulum specific Ca2+-ATPases --
precluded this effect. Similar pretreatment with ryanodine, a blocker of
'ryanodine-sensitive' channels, also precluded the caffeine effect. Despite a
presence or absence of caffeine, applications of thapsigargin, ryanodine or
CPA reduced the AP-evoked changes in [Ca2+]i.
From these new experimental observations, we can conclude that the
CICR through ryanodine-sensitive channels contributes to the AP-induced
changes of [Ca2+]; in hippocampal CA1 pyramidal neurons. [Scientific formulae used in this abstract could not be reproduced.]
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Extent |
6185584 bytes
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Genre | |
Type | |
File Format |
application/pdf
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Language |
eng
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Date Available |
2009-07-17
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Provider |
Vancouver : University of British Columbia Library
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Rights |
For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use.
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DOI |
10.14288/1.0099558
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URI | |
Degree | |
Program | |
Affiliation | |
Degree Grantor |
University of British Columbia
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Graduation Date |
1999-05
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Campus | |
Scholarly Level |
Graduate
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Aggregated Source Repository |
DSpace
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Item Media
Item Citations and Data
Rights
For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use.