Spatial dynamics of second messengers: IP3 and cAMP as long-range and associative messengers

Recent imaging experiments have revealed the distinct spatial dynamics of second-messenger actions. In general, actions of Ca2+ tend to be local, whereas those of other messengers such as inositol 1,4,5-trisphosphate (IP3) and cAMP are long range. In pancreatic acinar cells, IP3 generated at the base can diffuse across the cell and evoke a spatially confined Ca2+ signal in the apical pole, triggering enzyme and fluid secretion. Similar mechanisms might also operate in other cell types. We propose that the distinct dynamics of messengers might be relevant to neuronal function: IP3 and cAMP could convey signals over long distances along neurites, and serve as mediators for association and co-operation, for example, during learning.