Electrophysiologic effects and electrolyte changes in total myocardial ischemia

Area of Science:

• Cardiovascular Physiology
• Cardiac Electrophysiology
• Cellular Physiology

Background:

• Cardiac ischemia disrupts normal heart function by altering the cellular environment.
• Understanding the electrophysiological consequences of ischemia is crucial for managing cardiac events.

Purpose of the Study:

• To investigate the effects of cardiac ischemia on ventricular membrane potential and sodium/potassium dynamics in rabbit hearts.
• To determine how ischemia impacts the sodium system's inactivation characteristics and upstroke velocity.

Main Methods:

• Measured ventricular membrane potential in perfused rabbit hearts under control and ischemic conditions.
• Determined sodium system inactivation and upstroke velocity (Vmax) relative to resting potential and sodium gradients.
• Estimated intracellular sodium ([Na]i) and potassium ([K]i) concentrations via electrolyte and water content analysis.

Main Results:

• Ischemia caused a significant sodium gain (58 mmol/kg dry weight) and potassium loss, increasing [Na]i and decreasing [K]i.
• The resting potential in ischemic cells shifted closer to the potassium equilibrium potential.
• Vmax decreased within 10 minutes of ischemia, not fully explained by depolarization or reduced sodium gradient.

Conclusions:

• Cardiac ischemia induces significant changes in ionic gradients and membrane electrical properties.
• These electrophysiological alterations contribute to the observed functional changes during ischemia.
• Ischemia's impact on Vmax is complex, involving both ionic shifts and altered membrane characteristics.