Metabolism and energetics of working myocardial cells in animals
Cardiac muscle requires a continuous supply of oxygen and therefore myocardial cells under normal conditions, utilise aerobic metabolic system that provides a constant supply of high energy phosphate for mechanical and chemical working of the heart.
The major fuel required for cardiac metabolism is free fatty acids followed by glucose and lactate with a minor contribution from amino acids, ketones and pyruvates.
- Myocardial metabolism has three phases:
- Energy Liberation or Production: It is the stage during which energy is released from the carbon-hydrogen bonds of substrates including fatty acids, glucose, lactate and other compounds used by the heart.
- Energy conservation or storage: It is the transfer of the energy into synthesis of high energy phosphate compounds such as ATP, creatine phosphate, AMP, ADP.
- Energy Utilization: It is the release of this stored chemical energy into shortening or development of tension of cardiac contraction.
Cardiac muscles cells contains larger number of mitochondria that are rich in enzymes of citric acid cycle and oxidative phosphorylation for muscle contraction. ATP is utilized by the myocardial cells for muscle contraction which is broken down to ADP and inorganic phosphate (Pi).
The increased amount of ADP and inorganic phosphate (Pi) formed stimulates oxidative phosphorylation, the citric acid cycle and glycolysis thereby increasing the high energy phosphate bond production. Creatine phosphate also provides an immediate source of high energy phosphate bonds.