In an effort to conduct as realistic muscle activation experiments as possible, it would be useful to have a mechanism for completely binding divalent calcium even in an aqueous environment and then be able to release it cleanly and rapidly. We propose to prepare photolabile chemical chelators for divalent calcium which we hope can be applied to experimental skinned muscle fiber preparations. In order to circumvent diffusion problems as much as possible, we propose to utilize "azocryptands" which will have high Ca2 ion binding constants in the resting state and then rapidly change conformation and binding constant upon ultraviolet irradiation. Using these photolabile ligands, which are intrinsically interesting chemical structures, we hope to be able to release calcium into the system rapidly and without appreciably affecting other cellular structures.