(1) The study examines arrhythmogenic coupling between the Na+-Ca2+ exchanger and IP3 receptor in rat pulmonary vein cardiomyocytes. (2) Application of the α1 stimulant norepinephrine activates Ca2+ release via the IP3 receptor, which increases intracellular Ca2+. This Ca2+ then activates the co-localized Na+-Ca2+ exchanger, producing transient depolarizations. (3) β1-adrenergic action of norepinephrine reinforces Ca2+-induced Ca2+ release, resulting in Ca2+ overload. Accumulated Ca2+ is subsequently released again via the IP3 receptor in a positive feedback loop.

1. Arrhythmogenic Coupling between
Na+-Ca2+ Exchanger and IP3 Receptor in
Rat Pulmonary Vein Cardiomyocyte
Yosuke Okamoto1,
Makoto Takano2,
Kouiti Kawamura3,
Takayoshi Ohba1,
Kyoichi Ono1.
Department of Cell Physiology, Akita University Graduate School of Medicine
1
2
Department of Physiology, Kurume University School of Medicine, Kurume
3
Department of Cellular and Organ Pathology, Akita University Graduate School of Medicine

2. Haïssaguerre M, Jais P et al.
N Engl J Med. (1998) 339: 695-666.

3. http://lifesciencedb.jp/bp3d/

4. http://lifesciencedb.jp/bp3d/

5. http://lifesciencedb.jp/bp3d/

6. http://lifesciencedb.jp/bp3d/

7. http://lifesciencedb.jp/bp3d/

8. http://lifesciencedb.jp/bp3d/

9. http://lifesciencedb.jp/bp3d/

10. http://lifesciencedb.jp/bp3d/

11. http://lifesciencedb.jp/bp3d/

12. http://lifesciencedb.jp/bp3d/

13. http://lifesciencedb.jp/bp3d/

14. http://lifesciencedb.jp/bp3d/

15. http://lifesciencedb.jp/bp3d/

16. http://lifesciencedb.jp/bp3d/

17. 4 μm
4 μm 4 μm
40 μm
2 μm 2 μm
2 μm

18. Nicolas Doisne et al.
Am J Physiol Heart Circ Physiol (2009) 297:102-108.

19. LA
LA
30
20
50 µm
10
PV
Cells (%)
0
PV
30
20
10
0
Ventricular Myocyte
1000 3000 5000
Area (µm2)
20 μm

20. A B C
LA LA PV LA PV
10 pA/pF
10 pA/pF
100 ms 200 ms
-60 -40 -20 mV 20 40 1.0
0.8
PV 2
Availability
-2
pA/pF
0.6
* -4 0.4
-120-100 -60 -40 -20
mV -2
* -4
pA/pF
-6 0.2
* *
20 mV
* -6
0.0
-60 -40 -20 0 20 40 -8
50 ms
* *
-10 * mV * -10
-12
*

21. NE 10 μM
A
40 mV
1 min
NE 10μM NE 10μM
D
40mV
1 min
B C
50 pA/pF
Voltage Clamp
-50 mV
40 mV
20 mV
50 ms 1s

22. NE 10μM
A
20 mV
2 min
B NE 10μM
Vm (mV)
40
-40
0.3
F405/F480
0.2
1S

23. Vm (mV)
-60 -40 -20 0 20 40
I-V Relationship of
Arrhythmogenic Inward Currents -20
Induced by NE -40
-60
Current (pA)
Na+/Ca2+ Exchanger -80
-100
-120
100 pA
40 mV
2S

24. Spontaneous Ca2+ releasing after
Cessation of Automatic Action Potentials
NE 10μM
SEA 0400 10μM
40
Vm (mV)
-40
0.3
F405/F480
0.2
10 S

25. The Effect of α1 and β1 Antagonists
NE 10μM
Prazosin 1μM
Atenolol 5 μM 1 min
40 mV
30 S

26. Cascade of α1 signal transduction
NE 10 μmol/L
U73122 1 μM
40 mV
30 S
2-APB 2 μM
40 mV
30 S
Calphostin C 1 μM
40 mV
2 min

27. Co-localization of Na+/Ca2+ Exchangers and IP3 R
Fluorescence intensity
103
4 NCX
3 IP3R
2
1
0
0 1 2 3 4 5 6 7 8 9 10
μm
x105
8
4
AutoCorrelation: NCX
0
-2
NCX1 -4
0 1 2 3 4 5 6 7 8 9 10
μm
x104
20 AutoCorrelation: IP3R
10
0
-10
IP3R2 0 1 2 3 4 5 6 7 8 9 10
μm
x105 CrossCorrelation: NCX vs IP3R
10
0
-10
Merge -20
0 1 2 3 4 5 6 7 8 9 10
μm
10 μm

28. “Ca release via the IP3R is activated by α1 stimulant, and the Ca2+ in
2+
turn spin up the NCX, which is co-localized with the IP3R, producing
transient depolarization. β1-adrenergic action of NE reinforce CICR,
resulting in Ca2+ overload. The accumulated Ca2+ would be released
again via the IP3R. ”
Okamoto Y et al. J Mol Cell Cardiol. 2012 (in press)