New ratiometric fluorescent calcium indicators with moderately attenuated binding affinities

Mono-halogenated derivatives of the calcium indicators fura-2 and indo-1 we re synthesized and their spectroscopic properties evaluated. Halogenation o rtho or para to the bridging oxygen in the BAPTA nucleus had a more pronoun ced weakening effect on binding affinity than in the meta position in the f ura derivatives. Two new excitation ratioable fluorescent calcium indicator s, benzothiaza-1 and 2, were also synthesized. K-d values of 400 nM to 5.3 mu M [Ca2+] were observed in these families of new probes. (C) 2000 Elsevie r Science Ltd. All rights reserved.