Fig. 1. CCE-induced stimulation of AC8 activity detected with the fluorescent Epac-1 probe. (Ai) Averaged and calibrated fura-2 measurements show Tg-induced (100 nM) emptying of intracellular Ca²⁺ stores and induction of increasing degrees of CCE upon addition of 0.2, 1 and 2 mM Ca²⁺. (Aii) Parallel changes in cAMP levels in three separate cells that express the Epac-1 biosensor during CCE with 1 mM Ca²⁺. A decrease in YFP:CFP emission-ratio represents an increase in cAMP. 10 nM PGE₁ was added at 60 seconds. (Aiii) After Tg-induced Ca²⁺-store depletion a Ca²⁺ dose-dependent rise in [cAMP] was seen due to increasing degrees of CCE. (Bi-iii) Parallel experiments to A, but 500 µM carbachol (CCh) was added instead of Tg, to deplete the Ca²⁺ stores before inducing CCE. Data are plotted as mean ± s.e.m., n values range from 22 to 40 cells. ^*P<0.01, ^**P<0.001.