Facing the complexity inherent to living cells, we applied a new mathematical approach to build a model well reflecting the dynamics of the signalling downstream of G protein coupled receptors. To test whether our model reflects responses of cells to applied stimuli we utilise real time imaging approaches. Single cell recordings provide insights into the temporal characteristics of responses as well as the variability of responses to a specific stimulus. The modelling resulted in a prediction of a new so far not described interaction between nPKCs and Epac, revealing as well a non-linear and non-monotone relation between Epac and calcium transients.