Calcium Uncaging with Visible Light

We have designed a nitroaromatic photochemical protecting group that absorbs visible light in the violet-blue range. The chromophore is a dinitro derivative of bisstyrylthiophene (or BIST) that absorbs light very effectively (ε440 = 66,000 M–1 cm–1 and two-photon cross section of 350 GM at 775 nm). We developed a "caged calcium" molecule by conjugation of BIST to a Ca2+ chelator that upon laser flash photolysis rapidly releases Ca2+ in <0.2 ms. Using the patch-clamp method the optical probe, loaded with Ca2+, was delivered into acutely isolated mouse cardiac myocytes, where either one- and two-photon uncaging of Ca2+ induced highly local or cell-wide physiological Ca2+ signaling events.