Control of ionic permeabilities in normal and ischemic heart

Area of Science:

• Cardiovascular Physiology
• Cardiac Electrophysiology
• Ion Channel Function

Background:

• Cardiac electrical activity is governed by major ionic conductances.
• Electrogenic active transport and metabolic inhibition influence cardiac action potentials.
• Ischemia can induce lactate and acidosis, affecting cardiac electrophysiology.

Purpose of the Study:

• To describe the electrophysiological effects of lactate and acidosis on cardiac tissues.
• To investigate the mechanisms underlying ischemia-induced arrhythmias.
• To elucidate the impact of acidosis on ion conductances and action potential repolarization.

Main Methods:

• Electrophysiological studies on dog Purkinje fibers and frog atrial fibers.
• Assessment of action potential characteristics under conditions of lactate exposure and CO2-induced acidosis.
• Analysis of changes in major ionic conductances (sodium, calcium, potassium).

Main Results:

• Lactate (20 mM, pH 7.0) induced transient arrhythmias in dog Purkinje fibers.
• Acidosis decreased sodium and calcium conductances, and rectifications in frog atrial fibers.
• CO2-induced acidosis (20% CO2, pH 6.6) altered repolarization in dog Purkinje fibers, decreasing potassium conductance and causing reexcitation.

Conclusions:

• Acidosis-induced decrease in potassium conductance is proposed to cause ectopic foci and arrhythmias during ischemia.
• Lactate and acidosis significantly impact cardiac ion channel function and electrical stability.
• Understanding these effects is crucial for managing cardiac dysfunction during ischemic events.