Fig. 3

Time courses of the beginning of the calcium transient and contraction of rat heart primordia loaded with fluo-3 AM at E 10.5 days (n = 5) and E 10.03–10.06 days (n = 21). The left edge of each line indicates the start time of observation. The thin line represents the period when the heart primordium did not contract. The white bar represents the period when the calcium transient was observed and the contraction was not observed. The black bar represents the period when the heart primordium contracted with calcium transients. In samples surrounded by a broken line, the calcium transient began more than 16 min after the start of observation. The frequencies of the first calcium transients and first contractions of these samples were 57.8 ± 4.9 and 54.1 ± 3.5/min, respectively (n = 8). Detailed data for the sample indicated with an asterisk are shown in Fig. 2