All-optical mapping of cAMP transport reveals rules of sub-cellular localization

Cyclic adenosine monophosphate (cAMP) is a second messenger that mediates diverse intracellular signals. Studies of cAMP transport in cells have produced wildly different results, from reports of nearly free diffusion to reports that cAMP remains localized in nanometer-scale domains. We developed an all-optical toolkit, cAMP-SITES, to locally perturb and map cAMP transport. In MDCK cells and in cultured neurons, cAMP had a diffusion coefficient of [~]130 {micro}m2/s, similar to the diffusion coefficients of other small molecules in cytoplasm. In neuronal dendrites, a balance between diffusion and degradation led to cAMP domains with a length-scale of 27 {+/-} 11 {micro}m (mean {+/-} s.d.). Geometrical confinement by membranes led to subcellular variations in cAMP concentration, but we found no evidence of nanoscale domains or of distinct membrane-associated and cytoplasmic pools. We discuss the scaling relations which govern diffusible signaling in tube-shaped structures.