Measurement of intracellular Ca2+ concentration using Indo-1 during simultaneous flash photolysis to release Ca2+ from DM-nitrophen.

We have constructed a modular instrument to measure intracellular [Ca2+] ([Ca2+]i) in single isolated cells while simultaneously imposing step changes in [Ca2+]i using "caged Ca2+". By combining the outputs of a xenon arc lamp with a frequency-tripled (Nd:YAG) laser, the instrument can operate with low maintained illumination to measure [Ca2+]i using a ratiometric Ca(2+)-sensitive fluorophore and also activate the release of Ca2+ from a caged-Ca2+ compound with a high energy pulse of ultraviolet light. This instrument is simple to assemble, introduces little electrical noise, provides a wide range of illumination power, produces only moderate photobleaching of the Ca2+ indicator and can be readily adapted to diverse cellular preparations. We demonstrate the use of this system to measure step changes in [Ca2+]i in adult rat ventricular myocytes and a human embryonic kidney cell line (293 cells) in culture.