ABSTRACT

BODIPY-DA and BODIPY-5HT resulted in the appearance or enhancement of fluorescence intensity in the green part of the spectrum at 500-530 nm (Fig. 7.2 curves 2 and 4). But the fluorescence intensity at 500530 nm increased slightly if the cells were preliminarily treated with nonfluorescent dopamine and serotonin (Fig. 7.2, curves 3 and 5). This leads to the assumption that neurotransmitters and their fluorescent analogues bind mostly to the same sites in the cell Green fluorescence was especially strong in peripheral cell areas, where the plasma membrane (and the cellulose wall in plant cells) is located (See colour Figs. 28 and 29 in Appendix 2). Laser-scanning confocal microscopy allowed one to see the concentration of the green fluorescence at the pollen surface of Plantago lanceolata and sea urchin eggs Paracentrotus lividus (Roshchina et al., 2005)

as also seen in colour Fig, 28 in Appendix 2. The location of fluorescent transmitters predominantly outside the cell and a significant decrease in fluorescence intensity after the pretreatment of cells with dopamine or serotonin suggest that fluorescent derivatives are bound on the cell surface by the structures that bind natural neurotransmitters (e.g., receptors or transporters). This binding (possibly fairly specific) prevents a large part of lipophilic BODIPY derivatives from penetrating into the cell. Due to the presence of a lipophilic fluorophore, these fluorescent probes should penetrate across the plasma membrane; however, they concentrate outside the cell. Thus, similar to non-fluorescent dopamine and serotonin, BODIPY-neurotransmitters are bound on the cell surface (possibly, by the corresponding plasma-membrane receptors). However, it cannot be ruled out that these compounds may be bound inside the cell, because fluorescent probes contain a lipophilic moiety and, therefore, should penetrate into the cell and bind with organelles.