Postnatal development has a marked effect on ventricular repolarization in mice

Area of Science:

• Cardiovascular Physiology
• Developmental Biology
• Electrophysiology

Background:

• Cardiac repolarization is crucial for heart function.
• Understanding developmental changes in immature hearts is vital for identifying abnormalities.
• Postnatal development significantly impacts cardiac electrophysiology.

Purpose of the Study:

• To characterize and compare potassium (K+) currents in mouse ventricular myocytes during postnatal development.
• To determine the effects of age on ventricular repolarization.
• To investigate the developmental expression of K+ channels and their contribution to action potential duration (APD).

Main Methods:

• Utilized current- and patch-clamp techniques on isolated mouse ventricular myocytes.
• Examined action potentials and K+ currents underlying repolarization.
• Employed RT-PCR to quantify mRNA expression of relevant K+ channels.

Main Results:

• Action potential duration (APD) decreased with increasing age, being shortest in adult myocytes.
• K+ currents and K+ channel mRNA abundance were significantly higher in adult versus day 1 myocytes.
• Specific K+ currents (I(K1), I(to), I(ss), I(Kur)) exhibited distinct developmental timelines, with I(Kur) maturing later.
• Increased I(Kur) did not correlate with decreased APD; developmental APD changes were linked to I(to), I(ss), and I(K1).
• Ventricular I(to) and I(Kur) densities were greater than in age-matched atrial cells.

Conclusions:

• Developmental changes in mouse ventricular APD are primarily driven by increases in I(to), I(ss), and I(K1).
• The ultrarapid delayed rectifier K+ current (I(Kur)) plays a less critical role in postnatal APD changes.
• Ventricular K+ current profiles differ significantly from atrial profiles during development.