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Ryanodine receptors/calcium release channels in heart failure and sudden cardiac death
1Center for Molecular Cardiology, Department of Pharmacology, Columbia University College of Physicians and Surgeons, New York, NY 10032, USA. arm42@columbia.edu
Abstract:
Calcium (Ca2+) ions are second messengers in signaling pathways in all types of cells. They regulate muscle contraction, electrical signals which determine the cardiac rhythm and cell growth pathways in the heart. In the past decade cDNA cloning has provided clues as to the molecular structure of the intracellular Ca2+ release channels (ryanodine receptors, RyR, and inositol 1,4,5-trisphosphate receptors, IP3R) on the sarcoplasmic and endoplasmic reticulum (SR/ER) and an understanding of how these molecules regulate Ca2+ homeostasis in the heart is beginning to emerge. The intracellular Ca2+ release channels form a distinct class of ion channels distinguished by their structure, size, and function. Both RyRs and IP3Rs have gigantic cytoplasmic domains that serve as scaffolds for modulatory proteins that regulate the channel pore located in the carboxy terminal 10% of the channel sequence. The channels are tetramers comprised of four RyR or IP3R subunits. RyR2 is required for excitation-contraction (EC) coupling in the heart. Using co-sedimentation and co-immunoprecipitation we have defined a macromolecular complex comprised of RyR2, FKBP12.6, PKA, the protein phosphatases PP1 and PP2A, and an anchoring protein mAKAP. We have shown that protein kinase A (PKA) phosphorylation of RyR2 dissociates FKBP12.6 and regulates the channel open probability (P(o)). In failing human hearts RyR2 is PKA hyperphosphorylated resulting in defective channel function due to increased sensitivity to Ca2+-induced activation.
Insights
Calcium ions (Ca2+) are vital cell messengers regulating heart function. In heart failure, RyR2 channels become hyperphosphorylated, leading to defective calcium regulation and impaired cardiac function.
Area of Science:
- Cardiovascular Physiology
- Molecular Cell Biology
- Biochemistry
Background:
- Calcium ions (Ca2+) act as crucial second messengers in cellular signaling pathways.
- Intracellular Ca2+ release channels, like ryanodine receptors (RyR) and inositol 1,4,5-trisphosphate receptors (IP3R), are key regulators of Ca2+ homeostasis.
- RyR2 is essential for excitation-contraction coupling in the heart.
Purpose of the Study:
- To elucidate the molecular mechanisms regulating Ca2+ homeostasis in the heart.
- To define the macromolecular complex associated with RyR2.
- To investigate the role of PKA phosphorylation in RyR2 channel function and its implications in heart failure.
Main Methods:
- cDNA cloning to understand channel structure.
- Co-sedimentation and co-immunoprecipitation assays to define macromolecular complexes.
- Analysis of protein kinase A (PKA) phosphorylation effects on RyR2 channel activity.
Main Results:
- A macromolecular complex involving RyR2, FKBP12.6, PKA, PP1, PP2A, and mAKAP was identified.
- PKA phosphorylation of RyR2 leads to FKBP12.6 dissociation and modulates channel open probability (P(o)).
- In failing human hearts, RyR2 exhibits PKA hyperphosphorylation, causing increased Ca2+-sensitivity and defective channel function.
Conclusions:
- RyR2 function is tightly regulated by its associated protein complex and PKA phosphorylation.
- Dysregulation of RyR2 phosphorylation contributes to cardiac dysfunction in heart failure.
- Understanding these molecular interactions is critical for developing therapeutic strategies for heart disease.