Real-Time Measurements of Intracellular cAMP Gradients Using FRET-Based cAMP Nanorulers

3',5'-cyclic adenosine monophosphate (cAMP) is one of the most important and ubiquitous second messengers in cells downstream of G protein-coupled receptors (GPCRs). In a single cell, cAMP can exert innumerous specific cell functions in response to more than one hundred different GPCRs. Cells achieve this extraordinary functional specificity of cAMP signaling by limiting the spread of these signals in space and time. To do so, cells establish nanometer-size cAMP gradients by immobilizing cAMP via cAMP binding proteins and via targeted activity of cAMP-degrading phosphodiesterases (PDEs). As cAMP gradients appear to be essential for cell function, new technologies are needed to accurately measure cAMP gradients in intact cells with nanometer-resolution. Here we describe FRET-based cAMP nanorulers to measure local, nanometer-size cAMP gradients in intact cells in the direct vicinity of PDEs.