Fig. 2. Acetylcholine-generated calcium transients in muscle fibres within the embryo. (A) The frequency of the calcium transients (mean ±s.e.m.), recorded from whole muscle fibres using Oregon Green 488 BAPTA dextran, was plotted against standard developmental time (hpf). (B) The frequency of the calcium transients (mean ±s.e.m.) measured using the high affinity Oregon Green 488 BAPTA dextran (black bars, nM range) compared with the lower affinity Fluo-4 dextran (grey bars, µM range) were plotted against standard developmental time (hpf). There was no significant difference between the frequency of the calcium signals measured with two indicators between 18 and 19 hpf, or at 21.5hpf (unpaired t-test). (C) Traces (n=13) were selected in which fluorescence changes, reported using Oregon Green BAPTA dextran, correspond to changes in cytosolic calcium ion and not to cell movements (see supplementary material Fig. S1). The duration of the signals, defined as the time taken to decay from maximum amplitude to half that value (see inset) decreased significantly between a developmental period of 18-21 hpf (Spearman Rank Correlation, r=–0.825, P<0.0001). (D) Calcium signals in the anterior trunk axial muscle display a characteristic developmental pattern between 16 and 22 hpf.