Altered myocardial force generation in end-stage human heart failure

Area of Science:

• Cardiovascular Physiology
• Molecular Cardiology
• Biophysics

Background:

• End-stage human heart failure is associated with altered cardiomyocyte contractility.
• Increased calcium (Ca²⁺) sensitivity of force production is a key feature in failing cardiomyocytes.

Purpose of the Study:

• To investigate the molecular mechanisms underlying enhanced Ca²⁺ sensitivity in heart failure.
• To determine the role of thin filament regulation and cross-bridge kinetics in this phenomenon.

Main Methods:

• Utilized Triton-skinned myocytes from end-stage failing and non-failing human donor hearts.
• Measured Ca²⁺-activated isometric force and rate of force redevelopment (k_tr) under varying conditions (pH, inorganic phosphate [P_i]).

Main Results:

• Maximal force and k_tr did not differ between failing and non-failing myocytes.
• At submaximal Ca²⁺, both force and k_tr were elevated in failing myocytes.
• Enhanced Ca²⁺ sensitivity was abolished by P_i, indicating altered actin-myosin interaction kinetics.

Conclusions:

• The P_i release step in the actin-myosin cross-bridge cycle is modified in end-stage heart failure.
• This alteration may be functionally significant during conditions of P_i accumulation (e.g., ischemia).
• Findings suggest implications for cardiac energetics and therapeutic strategies targeting sarcomeric function in heart failure.