Multiple alterations in Ca2+ handling determine the negative staircase in a cellular heart failure model

Area of Science:

• Cardiology
• Molecular Biology
• Physiology

Background:

• The force frequency relationship (FFR) is typically positive in healthy hearts.
• A flat or negative FFR is a characteristic of heart failure.
• Potential mediators include reduced SERCA2a, increased Na(+)/Ca(2+) exchanger (NCX), and elevated intracellular Na(+) (Na(+)(i)).

Purpose of the Study:

• To investigate if individual mechanisms are sufficient to cause a negative FFR in nonfailing myocytes.
• To determine if combined mechanisms are required to replicate the failing heart's negative FFR.
• To model the failing heart's phenotype in healthy cat myocytes.

Main Methods:

• Pharmacological inhibition of SERCA2a (thapsigargin, CPA) or siRNA.
• Elevation of Na(+)(i) using ouabain or monensin.
• Overexpression of NCX via gene transfer (Ad.NCX).

Main Results:

• Individual interventions (SERCA2a inhibition, Na(+)(i) elevation, NCX overexpression) did not alter the positive FFR of healthy myocytes.
• Combinations of interventions (e.g., TG + Oua, Oua + Ad.NCX, TG + Ad.NCX) converted the positive FFR to negative.
• The negative FFR occurred at lower frequencies when all three interventions were combined.

Conclusions:

• Altered calcium handling at multiple levels is necessary to explain the negative FFR in heart failure.
• Synergistic effects of disrupted calcium homeostasis contribute to the negative FFR.
• These findings highlight the complex interplay of ion handling abnormalities in cardiac dysfunction.