抄録
Previous studies reported that rat heart begins to beat during embryonic day 9.5 (E9.5 day) and day 10.5 (E10.5 day). Several studies showed the increase in heart rate and the decrease in calcium transient duration during E10.5 day and adulthood. Few study, however, showed the change of heart rate and calcium transient during E9.5 day and E10.5 day. Therefore, we evaluated changes of beating area, heart rate and calcium transient around the time of the beginning of heart beat, especially from E9.5 to E10.5 day. Whole embryos were removed from uterus and then embryos were incubated in 37 °C Tyrode solution. The heart beat was observed using CCD camera system. Hearts at E10.0 day did not beat at removing from uterus and did not start to beat for 90 min. Hearts at E10.2 had already beaten (68.5/min). Hearts at E10.1 day did not beat at removing from uterus but started to beat in almost regular rhythm (31.3/min) within 90 min. Beating area of hearts at E10.1 day was firstly small and enlarged with time. Fluo-3 AM was used for observation of calcium transient. The calcium transient duration decreased with development. The change of calcium transient during E10.1 day and E10.5 day is similar to that during E10.5 day and adulthood. In conclusion, E10.1 day is the physiological period of the beginning of heart beat. [J Physiol Sci. 2008;58 Suppl:S48]
