Figure 5

Heart rate analysis at st.24. A and B: The pacing of each heartbeat for 110 s in st.24 embryos incubated at 15°C. The beginning of contraction of the atrium is indicated by the bar. A: Hd-rR. B: ODT. C: Dispersion of heartbeat intervals. Ten heartbeats are shown for seven different embryos; the numbers 1–3 for Hd-rR and ODT refer to the numbers 1–3 in panels A and B, respectively. Solid diamonds show severe bradyarrhythmia, which was defined as an interbeat interval whose duration was more than twice that of the minimal interbeat interval. Each heartbeat was divided by the average heartbeat at 15°C and 26°C. Data for the Hd-rR and ODT strains are shown on the left and right, respectively. D: Coefficients of variance of heartbeats in seven embryos incubated at 15°C after eliminating bradyarrhythmia from the analysis are shown in solid diamonds in C. E: Average heart rates at 15°C, including prolonged heartbeats, among seven embryos of each strain in C. SDs are shown as error bars. Asterisks indicate the level of significance (*: p < 0.05).