Single Image Capture of Bioactive Ion Crosstalk within Inter-Organelle Membrane Contacts at Nanometer Resolution.

Rapid bioactive ion exchange is a form of communication that regulates a wide range of biological processes. Despite advances in super-resolution optical microscopy, visualizing ion exchange remains challenging due to the extremely fast nature of these events. Here, a "converting a dynamic event into a static image construction" (CDtSC) strategy is developed that uses the color transformation of a single dichromatic molecular probe to visualize bioactive ion inter-organelle exchange in live cells. As a proof of concept, a reactive sulfur species (RSS) is analyzed at the mitochondria-lysosome contact sites (MLCs). A non-toxic and sensitive probe based on coumarin-hemicyanine structure is designed that responds to RSS localized in both mitochondria and lysosomes while fluorescing different colors. Using this probe, RSS give-and-take at MLCs is visualized, thus providing the first evidence that RSS is involved in inter-organelle contacts and communication. Taken together, the CDtSC provides a strategy to visualize and analyze rapid inter-organelle ion exchange events in live cells at nanometer resolution.