Photo-voltages of bilayer lipid membranes in the presence of cyanine dyes

Acrylamide quenching of tryptophan photochemistry and photophysics

Studies of acrylamide quenching of tryptophan (Trp) fluorescence, photochemistry, and photoionization have been conducted. Quenching of Trp fluorescence in aqueous solution by addition of acrylamide in the concentration range 0.0-0.5 M was measured and resulted in a Stern-Volmer quenching constant of KSV = 21 +/- 3 M-1. Photolysis experiments were performed in which Trp was photolyzed at 295 nm in the presence of varying concentrations of acrylamide. The loss of Trp was monitored using reverse-phase high performance liquid chromatography (RP-HPLC) and was observed to follow first order kinetics. Production of N-formylkynurenine (NFK) was observed by RP-HPLC in irradiated Trp samples both in the presence and absence of added acrylamide. In addition, no new photochemical product was detected. This was taken as evidence that acrylamide did not alter the photochemical pathway but just reduced the reaction rate as expected for a physical quenching mechanism. Plotting the reciprocal of photolysis rate constant versus acrylamide concentration produced a Stern-Volmer constant for quenching of Trp photochemistry of KSV = 6 +/- 2 M-1. The KSV values for both fluorescence quenching and photolysis quenching were thus large, implying efficient quenching of both processes by acrylamide. Assuming an excited singlet state lifetime of 2.8 ns, the calculated second-order quenching rate constants for fluorescence and photolysis were kq = 7.5 x 10(9) and 2.1 x 10(9) M-1 s-1 respectively. The possible involvement of photoionization in the photolysis mechanism was investigated by studies of acrylamide quenching of voltage transients produced by xenon flash lamp excitation of Trp at aqueous/teflon or aqueous/mica interfaces.(ABSTRACT TRUNCATED AT 250 WORDS)

Improved fluorescent probes for the measurement of rapid changes in membrane potential

To improve the quality of fluorescent voltage-sensitive probes twenty new styryl dyes were synthesized. Some of the new probes are significantly better than any used in the past. A signal-to-noise ratio of 90 root mean square (rms) noise was obtained for an optical recording of action potentials from neuroblastoma cells maintained in monolayer culture. The fluorescence fractional change of the optical signal is as large as 14%/100 mV. Photodynamic damage and bleaching are much less significant with the new probes. These fluorescent probes can be used to measure small and rapid changes in membrane potential from single cells maintained in monolayer cultures, from single cells in invertebrate ganglia, from their arborization, and from other preparations. The optical measurement can be made with a standard fluorescent microscope equipped with DC mercury illumination. Guidelines for the design of even better fluorescent probes and more efficient instruments are suggested.

Lipid and salt effects on carbocyanine dye-induced photo-voltages in bilayer membranes

Voltage transients induced by flash illumination of bilayer membranes with sorbed dye, 3,3' -dimethyl-2,2' -oxacarbocyanine chloride (diO-C1-3-CI), vary with membrane lipid composition and aqueous solution salt concentration. The voltage transients are probably induced by physical movements of sorbed dye molecules following photo-isomerization. Increased salt (NaCl and NaBr) concentrations in the aqueous solutions reduced the photo-voltage amplitudes by reducing the amount of dye sorbed to the membranes, and by decreasing the effective membrane thickness. The photo-voltage risetimes and falltimes varied systematically with salt concentration and membrane lipid composition, reflecting structural changes in the membrane's surface layer.

Cyanine dye structural and voltage-induced variations in photo-voltages of bilayer membranes

Flash illumination alters the voltage across bilayer lipid membranes in the presence of certain cyanine dyes. The waveforms of the photo-voltage vary systematically with dye structure and imposed transmembrane voltage. Experimental results are reported for 27 positively charged cyanine dyes, primarily oxazole derivatives, using lecithin/oxidized cholesterol bilayer membranes and 10-mM sodium chloride solutions. Several dyes do not induce any photo-voltages. Examples are 3,3' diethyl 9 ethyl 2,2' oxacarbocyanine iodide, 3,3' diethyl 2 oxa 2" thiacyanine iodide, and 3,3' dimethyl 2,2' indocarbocyanine iodide. Several dyes, when added to one side of the membranes, induce monophasic waveforms. Examples are 3,3' dimethyl 2,2' oxacarbocyanine chloride, and 3,4,3',4' tetramethyl 2,2' oxazalinocarbocyanine iodide. Other dyes induce a photo-voltage only if transmembrane voltages are imposed. These waveforms are biphasic with some dyes (3,3' diethyl 2,2' oxacarbocyanine iodide, for example) and monophasic with other dyes (3,3' dibutyl 2,2' oxacarbocyanine iodide, for example). The photo-voltage waveforms are explained by models that consider the movement of charged dye molecules within the membrane, following optical excitation. The dye movements are probably induced through charge rearrangements in the dye associated with long-lived triplet states, isomerization, or through excimer formation. These results provide information on the location and orientation of the dye molecules within bilayer membranes. The variations which occur in the waveforms with applied voltage indicate that these membranes are fluid in the direction perpendicular to the membrane plane.