Fig. 3. cAMP oscillations depend on changes in cytosolic [Ca²⁺] and PDE activity. (A) Two neighbouring Epac-1 probe-expressing cells, showing synchronous cAMP oscillations imposed by Ca²⁺ changes due to Tg-induced CCE. (Ba) YFP emission image, showing cytosolic distribution of the fluorescent Epac-1 probe in AC8-expressing HEK293 cells. (Bb-i) Pseudocolour images of the FRET emission ratio at various time points indicated in A, showing oscillating cAMP levels in the imaged cells. Bar, 20 µm. (C) Comparison of on-off-rates of Ca²⁺- and cAMP-transients presented as t_1/2. Data are shown as mean ± s.e.m. (n=12); P values were calculated using Student's t-test. (D) Effect of 100 µM IBMX on cAMP- and Ca²⁺-oscillations.