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The Carmeliet-Coraboeuf-Weidmann Lecture
Calcium signalling in the heart: From basic mechanisms to arrhythmias
David Eisner
• Introduction
• SR Ca is a major regulator of the Ca transient
size
• How is SR Ca controlled?
• Does modifying the RyR affect systolic Ca?
• Leaky RyR and systolic function
• The link between leaky RyRs and arrhythmias
Ca cycling in the heart
Ca2+
SRRyR
L-Cachannel
Ca2+
SERCACa2+
3Na+
NCX
phospholamban
in steady state
influx = efflux
cytoplasmic Ca po
SR Ca ↑ po
caffeine po
L-type Ca current(Ca entry)
Na-Ca exchange(Ca efflux)
Measurement of Ca efflux and influx
Im(600 pA)
0.5 sec
0.0
[Ca2+]i(µM)
0.8
0
4
sarcolemmalCa flux
(µmol/L)
25 pA
100 ms
Sarcolemmal Ca entry = exit
Ca2+
SRRyR
L-Cachannel
Ca2+
SERCA
Ca2+
3Na+
NCX
phospholamban
What controls the size of the Ca transient?
Ca2
+
• Introduction
• SR Ca is a major regulator of the Ca transient
size
• How is SR Ca controlled?
• Does modifying the RyR affect systolic Ca?
• Leaky RyR and systolic function
• The link between leaky RyRs and arrhythmias
SR Ca content (µmol/L)
0 25 500.0
0.8
0 25 50
Ca transientamplitude(µM)
0.0
0.8
Trafford et al (2000). J. Physiol. 522, 259-270
(SR Ca)3Ca transient
Ca transientamplitude(µM)
SR Ca content (µmol/L)
Consequences of steep relationship
small changes of SR content inotropically significant
Ca transientamplitude(µM)
SR Ca content (µmol/L)
Consequences of steep relationship
small changes of SR content inotropically significant
Must control SR Ca content precisely
• Introduction
• SR Ca is a major regulator of the Ca transient
size
• How is SR Ca controlled?
• Does modifying the RyR affect systolic Ca?
• Leaky RyR and systolic function
• The link between leaky RyRs and arrhythmias
How is SR content controlled?
regulation of SERCA by phosphorylation of phospholamban (PKA & CaMKII)
“autoregulation” – effects of SR release on sarcolemmal fluxes
empty SR with caffeine: how does it refill?
(a)
(a)
1
[Ca2+]i(µmol.l-1)
0
10 sec
(a)
[Ca2+]i(µmol.l-1)
0
1
Im(1.5 nA)
(b)
1 sec
(b)ICa-L
(1.25nA)
50 ms
influx
tailcurrent
(0.15nA)
(b)
200 ms
efflux
Trafford et al (1997) Circ Res 81, 477-484
SR Ca content controls sarcolemmal fluxes
systolic Ca inactivate L-type current & Ca influx
systolic Ca Ca efflux on NCX
(a) (b)
SR empty SR full
RyR
L-Cachannel
Ca2+
SERCA
Ca2+
3Na+
NCX
-
Ca2+
Eisner et al (1998) Cardiovasc Res 38, 589-604
Eisner et al (2000) Circ Res 87, 1087-1094
control of Ca entry and efflux by the systolic Ca transient
controls SR Ca content: a simple feedback mechanism
+
RyR
L-Cachannel
Ca2+
SERCA
Ca2+
3Na+
NCX
-
Ca2+
Relevance of feedback mechanism to HF
+
↑NCX
↑ RyR po
↓SERCA
↓ SR Ca
• Introduction
• SR Ca is a major regulator of the Ca transient
size
• How is SR Ca controlled?
• Does modifying the RyR affect systolic Ca?
• Leaky RyR and systolic function
• The link between leaky RyRs and arrhythmias
RyR
Ca2+Ca2+
Does systolic modulation of the RyR affect systolic Ca?
P
phosphorylation ↑ RyR po contributes to inotropic effects of
β-adrenergic stimulation?
But does ↑ RyR po →↑ systolic Ca?
[Ca2+]i
(uM)
SR Cacontent
(µmol/L)70
110
sarcolemmalCa flux
0
120.0
1.5
500 µM caffeine
efflux > influx
efflux = influx↓SR Ca
(µmol/L)
4 sec
efflux = influx
RyR opening
Ca transient
Ca efflux
SR Ca
efflux
influx
[[[
Increasing RyR opening does
not increase Ca transient in the
steady state
• Introduction
• SR Ca is a major regulator of the Ca transient
size
• How is SR Ca controlled?
• Does modifying the RyR affect systolic Ca?
• Leaky RyR and systolic function
• The link between leaky RyRs and arrhythmias
Closed
Open
Marx et al (2000) Cell 12, 365-376
Heart failure makes RyRs leaky
Heart failure Control
What are the effects of leak on Ca cycling?
• Introduction
• SR Ca is a major regulator of the Ca transient
size
• How is SR Ca controlled?
• Does modifying the RyR affect systolic Ca?
• Leaky RyR and systolic function
• The link between leaky RyRs and arrhythmias
Ca and arrhythmias
Why?
Heart Failure
use positive inotropes to
↑SR & systolic Ca
Arrhythmias
Ca2+
Ca2+
3 Na+
Ca2+ Ca2+
SR
RyR
SERCA
Ca2+
3 Na+NCX
Ca leak → diastolic Ca waves
Watch video
Díaz et al (1997). J. Physiol. 501, 3-16
SR Ca content (µmol/L)
Ca waves occur above a threshold SR Ca content
Ferrier et al (1973; Circ. Res. 38, 156-162)
Ca efflux on NCX
DAD
Ca waves are arrhythmogenicwave
depolarizing current
How do DADs produce arrhythmias?
1. Direct depolarization
Ca (340/380 nm)
2.4
4.0
Em (mV)
-90
40
500 ms
Ca wave
DAD
Ectopic beat
2. Increased APD heterogeneity
How do DADs produce arrhythmias?
Johnson……Volders (2013) Circ Res. 112:246-256.
systolic Ca release ICa APD Ca wave
20
-90
50
Vm (mV)
Ca (F/Fo)
470 ms 640 ms
1 s
Ca wave
1
• Digitalis toxicity• Reperfusion arrhythmias • Inotropic agents
↑SR Ca → ↑ Ca leak
↑ RyR po ↑ Ca leak
Ca waves arise from ↑ diastolic Ca leak from SR
• Heart Failure• RyR mutations CPVT (catecholaminergic
polymorphic ventricular tachycardia)
CPVT
(catecholaminergic polymorphic ventricular tachycardia)
Priori, S. G. et al. Circulation 2002;106:69-74
Why do leaky RyRs → arrhythmias?
How does β stimulation → arrhythmias?
Two ways to produce Ca waves
SR Ca content (µmol/L)0 50 150100
0
1
Waveprobability
0
normalSR Ca
↑SR Ca
↓ threshold
WT WTR4496C R4496C
0
160
Ca wave threshold(µmol/L) +iso +iso
Lower SR threshold in RyR R4496C mouse
Kashimura et al (2010) Circ Res 107, 1483-1489
SR Ca content is higher after β- stimulation
SR Cacontentmol/L
0
80
iso
**
SR Ca threshold
β- stimulation acts by ↑ SR content (via ↑ SERCA)
Venetucci, Trafford & Eisner (2007) Circ Res 100, 105-111
Origin of Ca waves in CPVT
SR Ca content (µmol/L)0 50 150100
0
1
Waveprobability
0
normalSR Ca
↑SR Ca
↓ threshold
β- stimulation
RyR mutation
• Steep dependence of Ca release on SR content
• Even a small decrease of SR Ca is important in HF
• SR Ca controlled by effects of systolic Ca transient on NCX and L-type current
• systolic Ca due to β-adrenergic stimulation not due to effect on RyR
• Leaky RyR diastolic Ca
• deranged RyR per se not arrhythmogenic
• CPVT decreases threshold
Summary
Gina Galli
David Greensmith
Takeshi Kashimura
Rajiv Sankaranarayanan
Andrew Trafford
Luigi Venetucci
Carlo Napolitano
Silvia Priori
Dan Johnson
Paul Volders
Acknowledgements
198324 June 2013
Felix BonkeLennart Bouman
Hilary Brown
Ursula RavensAlessandro MugelliKarin SipidoSylvain Richard
Antonio Zaza
Barbara Casadei
Elisabetta CerbaiPaul Volders Alex de Hemptinne
Guy Vassort
Godfrey Smith