Developmental changes in action potential and membrane currents in fetal, neonatal and adult guinea-pig ventricular myocytes.
Developmental changes in electrophysiological properties were investigated in enzymatically isolated ventricular cardiomyocytes from fetal (45-55 days after conception), neonatal (1-5 days after birth) and adult (45-60 days after birth) guinea-pigs. Action potentials were elicited at 1 Hz in current-clamp mode, and membrane currents were measured using whole cell voltage clamp method. Action potential durations at 50% and 90% repolarization decreased between fetal and neonatal periods and increased between neonatal and adult periods, while there was no substantial age-related change in resting membrane potential and action potential overshoot. Because cell membrane capacitance increased with age, indicating a developmental increase in cell size, current density was normalized to membrane capacitance for each cell. The L-type calcium current (lCaL) density at 0 and + 10 mV was significantly smaller in fetal and neonatal cells than in adult ones, although the voltage dependence and inactivation kinetics were similar among the three age groups. The delayed rectifier K+ current (lK) density at 0 and + 30 mV was significantly smaller in fetal cells than in neonatal and adult ones. No significant difference in the inward rectifier K+ current (lK1) density was observed among the three age groups. Thus, the electrophysiological properties of the guinea-pig ventricular myocytes were demonstrated to change during pre- and postnatal development. The observed changes in action potential duration could be explained by changes in the balance between lK and lCaL.
Kato
Y
Y
Department of Pharmacology, Toho University School of Pharmaceutical Sciences, Chiba, Japan.
Masumiya
H
H
Agata
N
N
Tanaka
H
H
Shigenobu
K
K
D000818:Animals; D000831:Animals, Newborn; D015220:Calcium Channels / Q000032:analysis*; D004594:Electrophysiology; D005260:Female; D005333:Fetus; D006168:Guinea Pigs; D006352:Heart Ventricles / Q000166:cytology / Q000196:embryology; D008564:Membrane Potentials; D015221:Potassium Channels / Q000032:analysis*; D024661:Potassium Channels, Inwardly Rectifying; D016276:Ventricular Function
D015220:Calcium Channels; D015221:Potassium Channels; D024661:Potassium Channels, Inwardly Rectifying