The cAMP response element binding protein modulates expression of the transient outward current: Implications for cardiac memory

doi:10.1016/j.cardiores.2005.05.028

The cAMP response element binding protein modulates expression of the transient outward current: Implications for cardiac memory

^aDepartments of Pharmacology, College of Physicians and Surgeons of Columbia University, New York, NY, USA
^bAnesthesiology, College of Physicians and Surgeons of Columbia University, New York, NY, USA
^cPediatrics, College of Physicians and Surgeons of Columbia University, New York, NY, USA
^dCenter for Molecular Therapeutics, College of Physicians and Surgeons of Columbia University, 630 West 168 Street, PH7West-321, New York, New York 10032, USA
^eDepartment of Physiology, State University of Stony Brook, NY, USA

*Corresponding author. Center for Molecular Therapeutics, College of Physicians and Surgeons of Columbia University, 630 West 168 Street, PH7West-321, New York, New York 10032, USA. Tel.: +1 212 305 8754; fax: +1 212 305 8351. Email address: mrr1{at}columbia.edu

Received March 18, 2005.
Revision received May 25, 2005.
Accepted May 31, 2005.

Abstract

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.

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