Factors that modulate Ca2+-dependent regulation of Cav2.1 (P/Q-type) Ca2+ channels Open Access

Kreiner, Lisa Hill (2008)

Permanent URL: https://etd.library.emory.edu/concern/etds/6w924c358?locale=en
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Abstract


Abstract
Factors that modulate Ca2+-dependent regulation of Ca v 2.1 (P/Q-type) Ca2+ channels

By Lisa H. Kreiner
Activity-dependent changes in the cytoplasmic Ca2+ concentration in neurons initiate a
multitude of processes ranging from gene transcription to neurotransmitter release. Voltage-gated
Ca2+ channels are important for these processes as they couple membrane depolarization to the
influx of Ca2+ ions into the neuron. Since Ca2+ is a second messenger in many cellular pathways,
factors that regulate Ca2+ signaling are essential for proper regulation of neuronal function.
Ca v 2.1 (P/Q-type) voltage-gated Ca2+ channels undergo a complex feedback regulation mediated
by Ca2+ bound calmodulin, which can cause short-term alterations in synaptic efficacy. Ca2+
influx through Ca v 2.1 produces an initial increase (Ca2+-dependent facilitation (CDF)) and
gradual decrease (Ca2+-dependent inactivation (CDI)) in Ca2+ current amplitude during high
frequency or prolonged stimulation. We investigated two factors that could potentially regulate
CDF and/or CDI in neurons, Ca2+ buffering proteins and Ca2+ induced Ca2+ release from
intracellular stores. Voltage clamp recordings from either Ca v 2.1 transfected HEK 293T cells or
dissociated Purkinje neurons were used to quantify CDF and CDI that occurs in response to
depolarization. The effects of the Ca2+ buffering proteins parvalbumin (PV) and calbindin (CB),
and the effects of caffeine-induced Ca2+ release from intracellular stores on CDF and CDI were
characterized. We found that regulation of CDI by PV and CB is more complex than expected of
simple Ca2+ buffers, and absence of these proteins in neurons results in altered Ca v 2.1 subunit
expression. Additionally, we found that caffeine, an activator of intracellular Ca2+ release,
enhances CDI in transfected cells, suggesting that Ca2+ release from intracellular stores
contributes to regulation of Ca v 2.1. Overall, our results suggest that CDI is highly influenced by
endogenous factors, which may allow tailoring of Ca2+ regulation to the needs of specific
neurons. Manipulation of these factors may prove useful in developing therapeutic strategies to


treat diseases such as migraine, absence epilepsy, spinocerebellar ataxia and other diseases where
Ca2+ signaling is altered.

Table of Contents



Table of Contents








Page

Chapter
1:
Introduction

1
Characterization of voltage-gated Ca2+
currents
1
Ca v 2.1
channels
5
Regulation of Ca v channels by Ca2+




10
Ca2+ regulation of Ca v 2.1






12
Physiological significance of Ca2+-dependent modulation of Ca v 2.1
14
Regulation of CDI of Ca v 2.1





15
Significance







22

Chapter 2: Endogenous and exogenous Ca2+ buffers differentially


modulate Ca2+-dependent inactivation of Ca v 2.1 Ca2+ channels

27

Abstract








27
Introduction
28
Materials
and
Methods 29

Results








32

Discussion








40

Chapter 3: Caffeine increases Ca2+-dependent inactivation of Ca v 2.1

(P/Q-type) Ca2+ channels






61
Abstract








61
Introduction
61
Materials
and
Methods 63

Results








65

Discussion








68

Chapter 4: Altered Ca2+-feedback to Ca v 2.1 Ca2+ channels in Purkinje

neurons lacking parvalbumin and calbindin




79
Abstract








79
Introduction
80
Materials
and
Methods 81

Results








87

Discussion








94

Chapter
5:
Discussion 116
I Ca and Ca2+ buffering proteins interact to regulate Ca v 2.1
116
Factors that affect feedback regulation of Ca v 2.1 by CICR

120
Potential consequences of altered Ca v 2.1 feedback regulation


for
neuronal
function
123

Role of Ca v 2.1 in network function and pathological conditions
125
References








127

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