Modulation of force-frequency relation by phospholamban in genetically engineered mice

Area of Science:

• Cardiovascular Physiology
• Molecular Cardiology
• Cardiac Excitation-Contraction Coupling

Background:

• Phospholamban (PLB) regulates sarcoplasmic reticulum Ca2+ pump activity.
• PLB levels influence myocardial contractility and cardiac function.
• Understanding PLB's role in the force-frequency relation is crucial for cardiac health.

Purpose of the Study:

• To investigate the in vivo role of phospholamban in modulating the force-frequency relation.
• To determine the impact of phospholamban levels on ventricular relaxation.
• To assess contractility and relaxation dynamics in genetically modified mice.

Main Methods:

• Studied transgenic mice overexpressing phospholamban (PLBOE) and gene-targeted mice lacking phospholamban (PLBKO).
• Assessed left ventricular (LV) contractility (+dP/dtmax) and relaxation (-dP/dtmax, tau) using a high-fidelity LV catheter.
• Generated force-frequency relations via incremental atrial pacing to determine critical heart rates (HRcrit).

Main Results:

• Both PLBKO and PLBOE groups showed altered average LV +dP/dtmax compared to controls.
• PLBKO mice exhibited a significantly higher HRcrit for LV +dP/dtmax, indicating enhanced force-frequency relation.
• PLBOE mice displayed a significantly lower HRcrit, demonstrating impaired force-frequency relation.
• Significant differences in contractile parameters were observed between mouse strains (FVB/N vs. SvJ).

Conclusions:

• Phospholamban levels are critical negative determinants of the force-frequency relation and myocardial contractility in vivo.
• Altering phospholamban levels significantly impacts cardiac contractility and relaxation dynamics.
• Contractile parameter variations between normal mouse strains necessitate careful consideration in research.