cAMP and calcium ions (Ca2+) are important second messengers in cells. In the β-cells of the pancreas, they regulate the release of insulin (light blue) into the blood stream, . Tenner et al. found that the level of Ca2+ (blue line) oscillates uniformly across the cell. The level of cAMP (red line) in the cytosol oscillates in phase with the level of Ca2+, as does the level in free pools of cAMP in the plasma membrane (bottom right). However, the level in spatially constrained pools of cAMP in the plasma membrane (shown here in pink) oscillates out-of-phase with Ca2+ and cAMP in the cytosol in the plasmaand elswhere in the membrane.