Caged-Ca2+: a new agent allowing liberation of free Ca2+ in biological systems by photolysis.

The alkaline earth cation complexes of DM-nitrophen [1-(2-nitro-4,5-dimethoxyphenyl)-N,N,N',N'-tetrakis-[(oxycarbonyl) methyl]- 1,2-ethanediamine)] release the bound cation in the millisecond time range upon irradiation by a short UV-light pulse. This technique allows to generate cation (eg. Ca2+) concentration jumps or pulses in solution or in cellular systems. The physico-chemical properties of DM-nitrophen and its Mg2+, Ca2+ and Ba2+ complexes are investigated by employing spectrophotometric and potentiometric techniques. In case of Ca2+ a stability constant of the complex up to nearly 10(11) M-1 is found. The magnitude of representative Mg2+ and Ca2+ concentration jumps which can be generated under realistic experimental conditions are calculated on the basis of the thermodynamic parameters reported here.