Measuring Ca2+ Oscillations in Mammalian Eggs

At fertilization mammalian eggs are activated by a prolonged series of oscillations in the intracellular free Ca²⁺ concentration. These oscillations can be monitored with any number of Ca²⁺ -sensitive fluorescent dyes. The oscillations last for several hours at fertilization and so there are some considerations with mammalian eggs that make them distinct from somatic cells that are commonly used in Ca²⁺ imaging experiments. I describe the use of two particular dyes that can be loaded into mouse eggs and that give the most valuable results. The first one is PE3 which can be loaded by incubation with the AM form of the dye which is membrane permeable. The other is rhod dextran which requires microinjection. Either one of these dyes offers advantages over the more commonly used fura2. I describe the way that the fluorescence from dye-loaded eggs is measured with a conventional epifluorescence microscope and a CCD camera.