Photoactivation of caged compounds in single living cells: An application to the study of cell locomotion

Caged compounds are molecules whose biological function is masked until UV light induces a photo-chemical reaction that converts the molecules into a biologically active state. These probes provide very powerful tools in cell biology research, since the activation can be precisely controlled temporally and spatially by limiting their exposure to light. This report describes a simple caged compound illuminator that can be attached to an inverted microscope; it can simultaneously provide both sufficient UV illumination for photoactivation and epifluorescence excitation to monitor indicator fluorescence. As an example, we show that the cytoplasmic calcium level can be raised very rapidly by the photoactivation of a new caged compound, caged calcium ionophore DMNPE-A23187, and that this [Ca2+](i) increase is associated with tail retraction of motile keratocytes.