Abstract: Mammalian cells which require contact with cell surface proteins for activation, differentiation and/or proliferation are cultured in contact with an immobilized mammalian cell, with an immobilized membrane vesicle from a mammalian cell or with immobilized membrane vesicles from at least two mammalian cell populations. The mammalian cell or membrane vesicle can be modified with a first partner of a biological binding pair, and immobilized on a solid carrier via a second partner of the biological binding pair. Culturing can be with a first immobilized membrane vesicle and subsequently with a second immobilized membrane vesicle. The membrane vesicle contains part of the natural surface of a mammalian cell that includes a signal triggering surface protein. The membrane vesicle can be immobilized via a binding partner of a cell surface molecule.

Abstract: The invention concerns diazapentalene derivatives of formula I ##STR1## in which X and Y represent leaving groups which are less nucleophilic than thiol compounds, as thiol-specific fluorochromes for the detection of compounds containing thiol groups, in particular in cells.