Effects of hydrostatic pressure on the location of PRODAN in lipid bilayers and cellular membranes

The effects of hydrostatic pressure on the location of 6-propionyl-2-(dimethylamino)naphthalene (PRODAN), an environmentally sensitive fluorescent probe, in phosphatidylcholine lipid bilayers and in goldfish brain synaptic membranes have been studied by fluorescence spectroscopy over the pressure range of 0.001-2 kbar. The emission spectrum of PRODAN in all the membrane systems examined exhibits two local maxima: one centers at around 435 nm and the other at about 510 nm. The intensity ratio of these two peaks, F435/F510, increases as pressure increases; in the particular case of dimyristoyl-L-alpha-phosphatidylcholine multilamellar vesicles [DMPC(MLV)], a dramatic change in F435/F510 appears at the lipid phase transition pressure. As pressure varies, an isoemissive point is seen in both egg yolk phosphatidylcholines and goldfish brain synaptic membranes; however, no isoemissive point is observed in DMPC(MLV). The presence of an isoemissive point is attributed to a pressure-induced relocation of PRODAN from the "polar" disposition (the 510-nm peak) to the "less polar" disposition (the 435-nm peak). The absence of an isoemissive point in the case of DMPC(MLV) is probably due to the lack of void space in the lipid matrix, as a result of tight lipid packing. Apparently, the probe relocation takes place in unsaturated systems, and PRODAN favors a more hydrophobic environment under pressure. However, on the basis of the emission spectra, PRODAN seems to remain more or less at the interfacial region over the pressure range examined. In goldfish brain synaptic membranes, the PRODAN polarization increases with pressure, giving dT/dP values of 15-20 degrees C kbar-1 for both dispositions.(ABSTRACT TRUNCATED AT 250 WORDS)