Intracellular calcium and electrogram in ischemic isolated rat heart

Area of Science:

• Cardiology
• Electrophysiology
• Cardiac Metabolism

Background:

• Electrogram (EG) changes during cardiac ischemia are critical for understanding heart function.
• Previous studies have explored EG alterations but mechanisms during reduced coronary flow require further elucidation.

Purpose of the Study:

• To investigate the electrogram (EG) changes in an isolated rat heart model during reduced coronary flow rate (CFR) and anoxic perfusion.
• To elucidate the underlying mechanisms of the observed voltage increase during ischemia.

Main Methods:

• Studied the electrogram (EG) of isolated rat hearts under conditions of reduced coronary flow rate (CFR) and anoxic perfusion.
• Utilized unipolar epicardial and transmural bipolar electrograms to assess voltage (V) changes.
• Investigated the role of intracellular calcium (Ca2+) by using Ca2+-free medium and verapamil.

Main Results:

• Reduced CFR induced a significant increase in voltage (V) in both unipolar epicardial and transmural bipolar electrograms.
• The voltage increase was specific to ischemic conditions and did not occur during anoxic perfusion.
• The observed ischemic voltage increase was independent of conduction disturbances and linked to modifications in transmembrane potential.

Conclusions:

• The ischemic voltage increase in the electrogram is primarily due to alterations in the cardiac cell transmembrane potential.
• Key events include inhibition of oxidative metabolism, increased intracellular Ca2+, elevated K+ conductance, and subsequent hyperpolarization.
• Intracellular Ca2+ modulation impacts the dynamics of the ischemic voltage increase, suggesting its crucial role.