Wavelength-programmed solute release from photosensitive liposomes

Liposomes of dipalmitoylphosphatidylcholine containing a photochromic lipid "Bis-Azo PC" release entrapped solutes on exposure to UV light. We have no w demonstrated that on addition of cholesterol (up to 25 mol%) to the lipos omal membrane the liposomes also release their contents in response to visi ble light in the region of 470 nm, to which liposomes lacking steroid are i nsensitive. In a mixed population of liposomes prepared with and without ch olesterol, this enables wavelength-dependent release of entrapped solutes o n sequential exposure to visible and UV light. Furthermore, the cholesterol -containing liposomes allow stepped partial release of entrapped solute fol lowing multiple periods of short visible illumination. It is suggested that the cholesterol-containing liposomes may be potentially useful for drug de livery and for L'Caging" of reagents. (C) 2000 Academic Press.