Factors that modulate Ca2+-dependent regulation ofCav2.1 (P/Q-type) Ca2+ channels Público
Kreiner, Lisa Hill (2008)
Abstract
Factors that modulate Ca2+-dependent regulation of Ca v 2.1 (P/Q-type) Ca2+ channelsBy 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
Chapter1:
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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