After making PCLS (Precision Cut Lung Slices), I want to observe the slices under a fluorescent microscope and quantify the calcium ion release during bronchoconstriction. To do so, I used two different dyes: Cal-520 and BAPTA-488 Oregon Green, which bind to Ca2+ in the cytoplasm. However, in both cases, no fluorescence could be observed under the microscope during bronchoconstriction.

Does anyone have experience in staining tissues (and not monolayer cell-cultures) and how can the dye effectively bind to the intracellular calcium ions ?