In conclusion, this study presents evidence to demonstrate that NRB-AF12, a fluorescent derivative of the selective rat toxicant NRB, has a highly similar fluorescence distribution to ER-Tr, a fluorescent derivative of glibenclamide, a known KATP channel inhibitor. On the basis of these results we hypothesize common cellular binding sites for NRB and glibenclamide that may potentially lead to common biological properties. Furthermore, we propose NRB-AF12 as a prototype for the development of new fluorescent probes selective for intracellular structures/organelles. Studies are in progress in our lab to investigate these aspects.