Inhibits efflux of ion channels; specificity is cell type dependent. Prepn: H. C. Englert et al., DE 3528048; eidem, US 4994493 (1987, 1991 both to Hoechst). Synthesis and characterization as potassium channel blocker: K. R. Giles et al., Bioorg. Med. Chem. Lett. 13, 293 (2003). Blocking kinetics of chloride channels: J. Dreinh"ofer et al., Biochim. Biophys. Acta 946, 135 (1988). Effect on chloride ion transport: B. R. Branchini et al., Biochem. Biophys. Res. Commun. 176, 459 (1991); eidem, Arch. Biochem. Biophys. 318, 221 (1995); J.-A. Kim et al., Biochem. Biophys. Res. Commun. 309, 291 (2003).