Low-affinity Fluorescent Indicator for Intracellular Calcium Ions
Abstract
A Ca2+ indicator, 7-amino-3-(2-benzothiazolyl)-6-[2-(2,3-di- fluoro-6-aminophenoxy)ethoxy]-coumarin-N,N,N’,N’-tetra- acetic acid was synthesized. The indicator has a large Kd value of 0.55 mM and shows an excitation spectral shift from 462 to 401 nm upon Ca2+ binding. The indicator, therefore, may be useful for the measurement of Ca2+ concentrations in the endoplasmic reticulum of living cells by ratiometric fluorescence spectroscopy with visible light excitation.