Differences in outward currents between neonatal and adult rabbit ventricular cells

Area of Science:

• Cardiovascular Physiology
• Cardiac Electrophysiology
• Ionic Currents

Background:

• Action potential duration (APD) in adult rabbit ventricular preparations increases with stimulation frequency.
• Neonatal rabbit preparations do not exhibit significant APD changes with altered stimulation frequency.
• Understanding the ionic basis for developmental differences in cardiac electrophysiology is crucial.

Purpose of the Study:

• To investigate the ionic mechanisms underlying the difference in frequency dependence of APD between adult and neonatal rabbits.
• To compare outward current densities and kinetics in adult versus neonatal rabbit cardiac myocytes.

Main Methods:

• Studied outward currents in single ventricular myocytes from papillary and epicardial tissues of adult and neonatal rabbits.
• Measured current densities and analyzed kinetic properties, including inactivation and recovery from inactivation.
• Focused on the voltage-activated transient outward current (I(to1)).

Main Results:

• Neonatal rabbit myocytes exhibited approximately half the outward current density compared to adult myocytes.
• The density of the transient outward current (I(to1)) was lower in papillary muscle cells than epicardial cells in both age groups.
• Key kinetic differences in I(to1) were observed: faster apparent inactivation and significantly faster recovery from inactivation in neonatal cells (time constant 113 ms vs. 1,356 ms in adults).

Conclusions:

• The faster recovery from inactivation of the transient outward current (I(to1)) in neonatal rabbit myocytes is proposed as the primary reason for the lack of frequency dependence in their action potential duration.
• These findings highlight significant developmental changes in cardiac ion channel function affecting electrophysiological properties.