Modularity in signal transmission.

Species nodes are colored according to their saturation/depletion status (EC90/EC10) in response to percentage of input. A. Input is Ca (100 nM…10), Da is set at 5. The figure shows a large number of species which have no response (less than 10%) to Ca input, two separate pathways are apparent. Species inactivate at low input levels in the ‘integration zone’. B. Input is Da (20 nM…5), Ca is set at 8. The graph shows input-dependent inactivation of links. Individual effects can be studied. For instance, PDE4 (in contrast to PDE1, PDE1CaM) shows responsivity to Da input because of a larger complex formation with cAMP, which subtracts from the enzyme concentration.