The cAMP response element binding protein modulates expression of the transient outward current: implications for cardiac memory.
OBJECTIVE
Long-term cardiac memory (LTCM), expressed as a specific pattern of T-wave change on ECG, is associated with 1) reduced transient outward potassium current (I(to)), 2) reduced mRNA for the pore-forming protein of I(to), Kv4.3, 3) reduced cAMP response element binding protein (CREB), and 4) diminished binding to its docking site on the DNA, the cAMP response element (CRE). We hypothesized a causal link between the decrease of the transcription factor CREB and down-regulation of I(to) and one of its channel subunits, KChIP2, in LTCM.


METHODS
After three weeks of left ventricular pacing to induce LTCM (8 paced, 7 sham control dogs), epicardial KChIP2 mRNA and protein levels were assessed by real-time PCR and Western blotting. Mimicking the CREB down-regulation in LTCM, CREB was knocked down in situ in other dogs using adenoviral anti-sense. Effects on the action potential notch, reflecting I(to), were investigated in situ using monophasic action potential (MAP) recordings and at the cellular level by the whole-cell patch clamp technique. CREB binding in the KChIP2 promoter region was ascertained by electrophoretic mobility-shift assays.


RESULTS
In LTCM, epicardial KChIP2 mRNA and protein were reduced by 62% and 76%, respectively, compared to shams (p < 0.05). CREB binding by the canine KChIP2 promoter region was demonstrated. CREB knockdown led to disappearance of the phase1 notch in MAP and ablation of I(to).


CONCLUSIONS
These results strengthen the hypothesis that down-regulation of CREB-mediated transcription underlies the attenuation of epicardial I(to) in LTCM. They also emphasize that ventricular pacing exerts effects at a subcellular level contributing to memory and conceivably to other forms of cardiac remodeling.
Patberg
Kornelis W
KW
Department of Pharmacology, College of Physicians and Surgeons of Columbia University, New York, NY 10032, USA.
Obreztchikova
Maria N
MN
Giardina
Sarah F
SF
Symes
Aviva J
AJ
Plotnikov
Alexei N
AN
Qu
Jihong
J
Chandra
Parag
P
McKinnon
David
D
Liou
Shian R
SR
Rybin
Andrew V
AV
Shlapakova
Iryna
I
Danilo
Peter
P
Yang
Jay
J
Rosen
Michael R
MR
D000200:Action Potentials; D000818:Animals; D001145:Arrhythmias, Cardiac / Q000378:metabolism* / Q000503:physiopathology*; D015153:Blotting, Western / Q000379:methods; D002135:Calcium-Binding Proteins / Q000378:metabolism; D002304:Cardiac Pacing, Artificial; D017362:Cyclic AMP Response Element-Binding Protein / Q000276:immunology / Q000378:metabolism*; D004285:Dogs; D015536:Down-Regulation; D004562:Electrocardiography; D024202:Electrophoretic Mobility Shift Assay; D023421:Models, Animal; D009206:Myocardium / Q000378:metabolism*; D016376:Oligonucleotides, Antisense / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D024642:Potassium Channels, Voltage-Gated / Q000032:analysis / Q000235:genetics / Q000378:metabolism*; D011401:Promoter Regions, Genetic; D020133:Reverse Transcriptase Polymerase Chain Reaction; D020257:Ventricular Remodeling
D002135:Calcium-Binding Proteins; D017362:Cyclic AMP Response Element-Binding Protein; D016376:Oligonucleotides, Antisense; D024642:Potassium Channels, Voltage-Gated