calcium-dependent gating of voltage-gated ion channels
TRANSCRIPT
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Calcium-dependent gating of Voltage-gated ion channels
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Ca2+ fluxes
Internalfree calcium
Effect
Ion fluxes
Gates
Membranepotential
Other transportmechanisms
Otherstimuli
Ca2+ Ions Transduce Signals
Ion Channels of Excitable Membranes, 3rd Edition, 2001Gene expression
Contraction
Neurotransmitter release
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Berne & Levy, Cardiovascular Physiology 6th Edition (1992)
Ca++Ca++
Ca channel
Ca2+ current controls the plateau phase of the cardiac action potential
Journal of Physiology (2000) 525.2, pp. 285-298
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Annu. Rev. Cell Dev. Biol. 2000. 16:521–55
Ca2+ channels control neurotransmitter release
CALCIUM CHANNEL
Ca2+
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Ca2+ channels regulate gene expressionin hippocampal neurons
L-typeCa2+ channelL-typeCa2+ channel
Ca2+
L-typechannel
Current Opinion in Neurobiology 1997, 7:419–429
NATURE |VOL 401 | 14 OCTOBER 1999 |703
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Ca2+ channel Structure
Annu. Rev. Cell Dev. Biol. 2000. 16:521–55
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Neuron, Vol. 25, 533–535, March, 2000
Family of Voltage-Gated Ca2+ Channels
L-type
T-type
P/Q-typeN-typeR-type
L-type
P/Q-type
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Ca2+-dependent gating ofthe L-type Ca2+ Channel
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Circ Res. 2001; 89:944-956.
Ca2+ channels control the plateau phase ofthe cardiac action potential
ICa,L
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SCIENCE, VOL. 202, 15 DECEMBER 1978
The permeating ion affects Ca2+ channel inactivation:Calcium Dependent Inactivation (CDI)
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Ba2+
Ca2+
-90
+20 mV
Voltage
Current
100 ms
CDI: accelerated inactivation with Ca2+
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Calcium Dependent Inactivation: A Ca2+-regulated feedback mechanism
• Ca2+ entering through channel
• Requires no cytoplasmic components– Ca2+ sensor is near channel pore
• Develops rapidly
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CDI is greatest at membrane potentialseliciting peak inward Ca2+ current
SCIENCE • VOL. 270 • 1502
Ba2+Ca2+ Ba2+Ca2+
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Ba2+Ca2+
CDI is greatest at membrane potentialseliciting peak inward Ca2+ current
SCIENCE • VOL. 270 • 1502
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Conditional Open Probability Analysis (COPA)
-90
+10
No inactivation
+10
-90Inactivation
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Conditional open probability analysis (COPA):Ca2+ entry enhances inactivation
SCIENCE, VOL. 250, 21 DECEMBER 1990
Ba2+
Ca2+
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100 mM Ba2+ out
Biophysical Journal Volume 66 April 1994 1051-1060
CDI in L-type channels reconstituted in bilayers
Requires no cytoplasmic components
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Ca2+ sensing apparatus resides within or nearCaV1.2 (1C) pore
•Rapid effects (< 5 msec)
•CDI in bilayers
•Minimal effects of Ca2+ chelators
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CE
EC
A region of 1C is
necessary and sufficient
SCIENCE VOL 270 1 DECEMBER 1995 1502
I II III IVI II III IVI II III IV
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EF-hand
Does Ca2+ bind directly to the 1C subunit?
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EF-hand
Does Ca2+ bind directly to the 1C subunit?
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Ca2+-binding in the EF-hand isnot necessary
Proc. Natl. Acad. Sci. USAVol. 94, pp. 2301–2305, March 1997
XCDI: √CDI:
√CDI:
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Identification of critical region(s) in the C-terminus
THE JOURNAL OF BIOLOGICAL CHEMISTRYVol. 272, No. 6, Issue of February 7, pp. 3560–3566, 1997
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Identification of critical region(s) in the C-terminus
Proc. Natl. Acad. Sci. USAVol. 95, pp. 3287–3294, March 1998
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IQ motif
N
C
N
C
N
C
N
C
IQ motif / calmodulin (CaM) binding domain: CaM as the Ca2+ sensor
NATURE |VOL 399 | 13 MAY 1999 | 159
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IQ motif is the CaM effector site
NATURE |VOL 399 | 13 MAY 1999 | 159
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NATURE |VOL 399 | 13 MAY 1999 | 159
CaM binds to the IQ motif in the C-tail
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N C
1477-1592 1592-1875
4- 4- 4-WT WT WT
1551-1660
CaM is constitutively bound to 1C
THE JOURNAL OF BIOLOGICAL CHEMISTRY Vol. 276, No. 33, Issue of August 17, pp. 30794–30802, 2001
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Comparison of cation binding affinities of Calmodulin EF handsEC50 values (M)
Ca2+ Sr2+ Ba2+
Effective ionic radius (Å ) 1.06 1.21 1.38
Phosphodiesterase activity via CaM*
~2.5 ~25 >1000
Mol Pharmacol 26:75-82, 1984
CDI correlates with the affinity of thedivalent ion for CaM
SCIENCE, VOL. 202, 15 DECEMBER 1978SCIENCE, VOL. 202, 15 DECEMBER 1978
*PDE is one well-studied example of a Ca2+/CaM regulated enzyme, allowing the testing of the ionic dependence of CaM activation; PDE has nothing to do with CDI.
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Calcium Dependent Inactivationof L-type Ca2+ Channels
• Calmodulin is the Ca2+ sensor
• CaM is pre-associated with 1C
• The IQ motif is the effector domain in 1C
• The EF-hand is a structural, non Ca2+-sensing domain
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SCIENCE VOL 294 31812 OCTOBER 2001
SCIENCE VOL 294 33312 OCTOBER 2001
Gene expression in hippocampal neurons: LTCs and CaM
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Ca2+-dependent gating ofP/Q-type Ca2+ Channels
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NATURE |VOL 411 | 24 MAY 2001 |485
CDI and CDF in P/Q channels
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CaM is the Ca2+ sensor?
NATURE |VOL 411 | 24 MAY 2001 |485
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Different kinetics:different effector site?
NATURE |VOL 399 | 13 MAY 1999 |155
NATURE |VOL 411 | 24 MAY 2001 |485
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Different kinetics:different Ca2+ sensor?
nature neuroscience • volume 5 no 3 • march 2002 • 210
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Ionic Dependence of IpCa Inactivation
is it really CaM?
Neuron, Vol. 20, 797–807, April, 1998
Time constants Ca2+ Sr2+ Ba2+
Fast (ms) 43.6 ± 6.4 48.8 ± 2.9 88.5 ± 8.6
Slow (ms) 477 ± 51 576 ± 49 673 ± 46
PDE activity via CaM ~2.5 ~25 >1000
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Calcium Dependent Gating of P/Q Ca2+ Channels
• Kinetics of inactivation and facilitation differ from L-type channel gating
• Calmodulin appears to be the Ca2+ sensor and the IQ motif is one effector domain in 1A
• CBD may be another effector domain
• The Ca2+-binding protein CaBP1 regulates inactivation in a Ca2+-independent manner
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Ca2+-dependent gating of SK channels
TINS Vol. 19, No. 4 1996
IAHPTonic spiking
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Ca2+-dependent gating of SK channels
NATURE |VOL 395 | 1 OCTOBER 1998
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CaM is the Ca2+ sensor
NATURE |VOL 395 | 1 OCTOBER 1998
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CaM is the Ca2+ sensor
NATURE |VOL 410 | 26 APRIL 2001
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Gating Switch
NATURE |VOL 410 | 26 APRIL 2001
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Ca2+/CaM modulation ofCNG channels
JBC Papers in Press. Pub. on March 7, 2003
Adaptation
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Mechanism of Action
JBC Papers in Press. Pub. on March 7, 2003
Loss of auto-excitatory interaction
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Other channels
• NMDA subtype of excitatory glutamate receptors
• BKCa channels