Contraction of developing avian heart muscle

Area of Science:

• Cardiology
• Developmental Biology
• Muscle Physiology

Background:

• Cardiac muscle contraction undergoes significant changes during development.
• Understanding these changes is crucial for comparative cardiology and developmental studies.

Purpose of the Study:

• To investigate the developmental changes in chick heart contraction.
• To compare these changes with those observed in mammalian myocardium.
• To elucidate the underlying molecular mechanisms, including the role of calcium and contractile proteins.

Main Methods:

• Experiments were conducted on intact and membrane-free ("skinned") chick ventricular trabeculae.
• Twitch force was measured at various extracellular calcium concentrations ([Ca2+]).
• Changes in calcium sensitivity and the effects of acidosis and inorganic phosphate (Pi) were analyzed.

Main Results:

• Chick heart development exhibits strong parallels with mammalian myocardium development.
• Normalized twitch force in chick left ventricle trabeculae significantly increases around hatching.
• Maximal contractile capability increases with development, likely due to contractile protein proliferation.
• Calcium sensitivity of the contractile apparatus decreases with development, associated with troponin T isoform switching.
• Acidosis and inorganic phosphate depress force generation, with acidosis's effect intensifying during development.

Conclusions:

• Developmental changes in chick heart contraction mirror those in mammals.
• Increased twitch force is attributed to enhanced contractile protein content.
• Shifts in troponin isoforms influence calcium sensitivity and the response to acidosis during cardiac development.