title: A nanosecond fluorescence study of the simultaneous influx of Ca2+ and Cd2+ into liposomes.
abstract: Nanosecond fluorescence decay characteristics of the calcium-binding probe Quin2 and two of its cation complexes were examined by time-resolved fluorescence spectroscopy. Binding of Ca2+ and Cd2+ resulted in fluorescence lifetime enhancements as compared to that of free Quin2 ('tau' = 0.9 ns). The Quin2-Ca2+ complex displays a monoexponential decay of tau = 7.4 ns, while the cadmium complex gives an average decay time of ca. 4 ns. Lifetime measurements made on heterogeneous cationic solutions demonstrate that decay times for individual complexes can be retrieved. Time-resolved measurements were used to monitor the kinetics of ionomycin-mediated calcium and cadmium transport across artificial membranes. Fluorescence decays, collected on the time-scale of second, were sufficient to measure individual ion fluxes or those of mixtures into liposomes. The combination of steady-state and time-resolved fluorescence techniques offers the unique advantage of simultaneously detecting other cations in the presence of calcium.
authors.affiliation: Department of Biology, Johns Hopkins University, Baltimore, MD 21218, USA.
authors.forename: K M
authors.initials: KM
authors.lastname: Hirshfield
authors.forename: D
authors.initials: D
authors.lastname: Toptygin
authors.forename: G
authors.initials: G
authors.lastname: Grandhige
authors.forename: B Z
authors.initials: BZ
authors.lastname: Packard
authors.forename: L
authors.initials: L
authors.lastname: Brand
mesh_terms: D000634:Aminoquinolines / Q000737:chemistry; D002104:Cadmium / Q000737:chemistry*; D002118:Calcium / Q000737:chemistry*; D005456:Fluorescent Dyes / Q000737:chemistry*; D015759:Ionomycin / Q000737:chemistry; D007476:Ionophores / Q000737:chemistry; D007502:Iron Chelating Agents / Q000737:chemistry; D007700:Kinetics; D008081:Liposomes / Q000737:chemistry*; D013050:Spectrometry, Fluorescence
chemical_list: D000634:Aminoquinolines; D005456:Fluorescent Dyes; D007476:Ionophores; D007502:Iron Chelating Agents; D008081:Liposomes; D002104:Cadmium; D015759:Ionomycin; C035739:Quin2; D002118:Calcium