FM 4-64 is a lipophilic styryl dye and a vital stain: it fluoresces only in living cells, so cells cannot be fixed then stained nor stained then fixed. You must stain and observe living cells. FM 4-64 does not permeate cell membranes but, instead, intercalates into the plasma membrane is then
taken into the cells by endocytosis. - [Read FM 4-64 Labeling of Yeast Vacuole Membranes Protocol]
Accumulation of lipophilic substances in the plasma membrane may affect the membrane lipid order and consequently affect the function of these proteins. Changes in the activity of the Na+/K+ -ATPase, which is the major active transport system responsible for the electrochemical potential in mammalian cells, can therefore be an indication of the effect that a chemical may have on the viability of the cell membrane and possibly the whole cell. - [Read Hamster Ovary Cell NA+/K+ -ATPase Test]
Accumulation of lipophilic substances, many of which may be environmental chemicals, affects the membrane lipid order and consequently affects the functions of these proteins. Since, the function of important cellular proteins, such as the H+-ATPase strongly depends upon the integrity of the lipid bilayer, the activity of the H+-ATPase may be used as a sensitive indicator of the effect that a chemical may have on the viability of the cell. - [Read Yeast Plasma Membrane H+ -ATPASE Toxicity Test]