Intracellular Ca2+
Signaling
Why Calcium?
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Na+ and Cl- are
sea water |
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Excluded to maintain low osmotic
pressure |
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[K+]i kept high
for electrical neutrality |
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[Ca2+]i
maintained very low |
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Prevents precipitation of organic
anions |
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Mg2+ helps solubilize
organic anions |
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How cells keep [Ca]i
low
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All eukaryotic cells have PM Ca2+-ATPase |
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Excitable cells also have Na+/Ca2+
exchanger (NCX) |
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ER Ca2+-ATPase (against a
high grad) |
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Mitochondrial high capacity (low
affinity) pump |
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When [Ca]i very high
(dangerous) levels (>10-5 M) |
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Inner mitochondrial membrane |
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Uses the electrochemical gradient
generated during electron-transfer of oxidative-phosphorylation |
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Calcium Concentrations
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[Ca2+]o / [Ca2+]i
>104 |
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[Ca2+]o ~10-3
M |
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[Ca2+]ER ~10-3
M |
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[Ca2+]i <10-7
M at rest |
Ca2+ - a
versatile signal
Ca2+ - a
versatile signal
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Synaptic vesicle release (ms) |
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Excitation-contraction coupling (ms) |
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Smooth muscle relaxation (ms-sec) |
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Excitation-transcription coupling
(min-h) |
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Gene transcription (h) |
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Fertilization (h) |
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How Ca2+ is
measured
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Ratiometric dyes |
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Cameleons |
How cells ↑ [Ca]i
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Voltage-gated Ca2+ Channels |
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Membrane potential drives Ca2+
down its chemical gradient |
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Different channels in different cells |
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Different properties for different
purposes |
Ca2+ shut-off
pathways
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Voltage-gated Ca2+ channels
inactivate |
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IP3 rapidly dephosphorylated |
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Ca2+ rapidly pumped out |
Ca2+
oscillations
Intracellular Ca2+
Targets
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EF hand-containing proteins |
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Calmodulin |
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C2 domain proteins |
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PKC |
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Synaptogamin |
Intracellular Ca2+
Targets
EF hand proteins
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Troponin C |
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Calmodulin |
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Calcineurin |
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Calpain |
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Recoverin |
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S100 |
Calmodulin (CaM)
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16.8 kDa Ca2+-binding
protein |
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Highly conserved in all eukaryotes |
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Up to 1% of protein |
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Binds 4 mol Ca2+/mol |
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Binding affinity ~ .25-1x106
M |
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Cooperativity with Hill constant ~ 2 |
Classical mode of CaM
regulation
Relief of autoinhibition
CaMKII
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Autoinhibition and |
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Frequency Decoder |
New modes of CaM
interaction
New modes of CaM
interaction
New modes of CaM regulation
Intracellular Ca2+
Targets
C2 Domains
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Protein kinase C |
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Synaptotagmin |
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Phospholipase A2 |
C2 domains - PKC
Synaptotagmin and
neurotransmitter release