Afterload-induced homeometric autoregulation in isolated cardiac muscle

Area of Science:

• Cardiology
• Cardiac Physiology
• Muscle Contraction

Background:

• Pressure-induced homeometric autoregulation (HAR) is documented in mammalian ventricles.
• Conflicting reports exist for isolated cardiac muscle, showing anti-HAR where the first beat post-contraction is strongest, declining over time.

Purpose of the Study:

• To investigate the conditions under which canine ventricular trabeculae exhibit HAR or anti-HAR.
• To determine the influence of stimulation rate, calcium levels, and temperature on these phenomena.

Main Methods:

• Isolated canine right ventricular trabeculae were subjected to varying stimulation rates, calcium concentrations, and temperatures.
• Contractile force was measured following transitions from isotonic to isometric contractions.

Main Results:

• Trabeculae demonstrated either HAR or anti-HAR depending on experimental conditions.
• Higher calcium, higher temperature, and lower stimulation rates favored anti-HAR.
• A unique critical stimulation rate existed for each temperature, differentiating HAR from anti-HAR.

Conclusions:

• The manifestation of HAR or anti-HAR in canine ventricular trabeculae is condition-dependent.
• Stimulation rate, calcium, and temperature are key modulators of cardiac muscle's response to altered loading conditions.