An electron-microscopic support of electrophysiological findings in prolonged Q-T interval in newborn mice

In previous studies we examined the ECG patterns of mouse embryos and newborns. We showed that the ECG of newborns with prolonged Q-T interval (PQT) is similar to that of embryos in the intermediate stage (days 13-16) while the ECG in normal newborns resembles that of the prenatal fetus (from day 17). On the basis of these results we hypothesized that PQT could be due to delayed or incomplete differentiation of myocardial cells. The present study compares the electrophysiological and microscopical properties of normal and PQT newborns' myocardial cells, with those of embryos at different stages. The results show that the Q-T interval and the duration of myocardial action potential in the PQT newborns are prolonged and similar to those of the embryos at the intermediate stage, while they are short in prenatal-embryos and normal newborns. In the PQT newborns and intermediate embryos, numerous undifferentiated cardiac myoblasts were identified under light and electron microscope. They were intermingled with myocytes. The normal newborns showed as do normal prenatal embryos only a few isolated similar myoblasts.