Differences in transient outward current properties between neonatal and adult human atrial myocytes

Knowledge of postnatal modulation of Ito in human atrial myocytes is quite limited. The present study investigated the differences in Ito properties between neonatal and adult human atrial myocytes. Methods. – Atrial myocytes were dissociated enzymatically from biopsies of human right atrial appendage. Ito and action potentials were recorded by whole-cell patch-clamp technique. The expressed protein levels of Kv4.3 and KChIP2 in atrial tissue were detected by western blot technique. Results. – Ito was present in all atrial cells (n = 37) from 10 neonatal patients (2.5–7 months). The mean value of Ito density in neonatal atrial cells was significantly larger than in adult atrial cells. The time constants for Ito current decay were significantly faster for neonatal cells, compared to adult cells. Ito recovery from inactivation at holding potential of – 80 mV was significantly slower for neonatal atrial cells than for adult atrial cells. There was no difference in the voltage dependence of Ito activation between neonatal and adult cells. The voltage-dependent inactivation slope factor was smaller for neonatal compared to adult atrial cells. A more significant frequency-dependent suppression of Ito peak current and a more significant lengthening of APD30 were observed in neonatal atrial cells compared to adult atrial cells. Western blots showed both Kv4.3 and KChIP2 are expressed in neonatal atria, but with significantly higher level of Kv4.3 and lower level of KChIP2 protein compared to adult. Conclusion. – There are significant differences in the properties of Ito between neonatal and adult human atrial cells, including a larger current density, faster inactivation and slower recovery from inactivation in the neonatal atrial cells. The physiological differences of Ito are consistent with the different expression protein levels of Kv4.3 and KChIP2.