Cellular basis for the monophasic action potential. Which electrode is the recording electrode?

Area of Science:

• Cardiovascular Physiology
• Electrophysiology

Background:

• The cellular basis of the monophasic action potential (MAP) is debated, specifically the roles of recording and indifferent electrodes.
• Clarifying electrode function is crucial for understanding cardiac electrophysiology.

Purpose of the Study:

• To determine which electrode (recording or indifferent) is responsible for MAP generation.
• To compare the accuracy of intramural versus contact MAP recordings.

Main Methods:

• Simultaneous recording of transmembrane action potentials (TAPs) and MAPs (intramural and contact) in canine ventricular wedge preparations.
• Utilizing local cooling and ATX-II injection to assess electrode function.
• Intramural MAPs recorded with wire electrodes referenced to KCl electrodes.

Main Results:

• Manipulations at the inactivating electrode site did not alter MAP, while changes at the non-inactivating electrode prolonged the MAP.
• Intramural MAPs showed prolongation proportional to TAPs.
• Contact MAPs exhibited apparent afterdepolarizations due to their wider field of view.

Conclusions:

• The non-inactivating electrode, not the contact electrode, functions as the MAP recording electrode.
• Intramural MAP recordings provide a more accurate representation of local cardiac electrical activity.
• MAPs reflect extracellular potential differences between active and inactive cardiac regions.