Near-membrane iminocoumarin-based low affinity fluorescent Ca2+ indicators

Two new potential near-membrane iminocournarin-based fluorescent Ca2+ indicators were synthesized and the spectral profiles of their free and Ca2+ bound forms were studied. The probes incorporate in their BAPTA-related structures, the 3-(benzimidazolyl)iminocoumarin or the 3-(benzothiazolyl)iminocoumarin moiety, substituted at the imino nitrogen with an n-dodecyl lipophilic chain. The compounds are excited with visible light and have Ca2+ dissociation constant values of 5.50 and 4.49 muM, respectively, the highest reported to date in the literature. Fluorescence spectra studies indicated a clear shift in their excitation wavelength maxima upon Ca2+ binding along with changes in fluorescence intensity that enable the compounds to be used as ratiometric near-membrane, low Ca2+ affinity probes. (C) 2002 Elsevier Science Ltd. All rights reserved.