Time course of postnatal changes in rat heart action potential and in transient outward current is different

Abstract

The rat ventricular action potential shortens after birth. The contribution of increases in the transient outward current (Ito) to postnatal action potential shortening was assessed by measuring Ito in isolated cells and by determining the effect of 2 mM 4-aminopyridine (4-AP) on the action potentials of papillary muscles. 4-AP had no effect on 1-day action potential duration at 25% repolarization (APD25), and 1-day cells had little Ito. In 8- to 10-day muscles, 4-AP caused a small, but significant, increase in APD25. Ito increased slightly between day 1 and days 8-10, but this increase was not significant. Most of the increase in Ito (79%) and in the response to 4-AP (64%) occurred between days 8-10 and adult; however, approximately 75% of the APD25 shortening took place by days 8-10. Thus, while Ito may contribute to repolarization in late neonatal and adult cells, the different time courses of action potential shortening and increases in Ito suggest that changes in Ito are unlikely to be responsible for most of the postnatal action potential shortening.

Decreased Sodium and Increased Transient Outward Potassium Currents in Iron-Loaded Cardiac Myocytes

“…Control values of resting potential and action potential durations for neonatal rat cells are consistent with those from reports using similar conditions. 21,22 Likewise, the control resting potential and action potential durations of gerbil cardiomyocytes are similar to values reported for adult rats. 21,22 …”

Functional Expression and Inactivation of L-type Ca²⁺ Currents During Murine Heart Development -Implications for Cardiac Ca²⁺ Homeostasis

“…increase of heart rate and ion channel expression during maturation, APs become shorter at the adult than at the embryonic, fetal or neonatal stage. The plateau phase of neonatal rat cardiomyocytes for example becomes very short or even absent in the adult heart [54]. Accordingly, we found that the plateau phase in APs of the early murine embryonic heart is significantly prolonged as compared to late embryonic and particularly adult stages (unpublished observation).…”

Influence of postnatal changes in action potential duration on Na-Ca exchange in rabbit ventricular myocytes

“…In human atrial myocytes, APD increases with age, particularly during the earliest years of life [12]. In contrast, however, newborn rat ventricular myocytes have a characteristically long AP that shortens considerably during development [22,37]. Our present findings demonstrate that, like most mammalian species except the rat, ventricular AP amplitude and duration increase after birth in the rabbit.…”