Fig. 7. Fluorescent labeling of filipin sterol complexes on fixed boar sperm cells. Filipin-labeled cells were mounted in coverslips and sealed with nail-polish. The filipin fluorescence was observed under 340-380 nm excitation and fluorescence signals >425 nm were selected by the emission filter. (A) Filipin labeling of a sperm cell from the low M540 fluorescent sperm subpopulation (identical to pattern A; Fig. 4a). (B) As in A but from the high M540 fluorescent subpopulation (identical to pattern B; Fig. 4b). (C) Filipin labeling was absent in the sperm head of cells that were capacitated in HBT-Bic supplemented 0.3% (w/v) albumin (pattern C). Note the labeling of the neck region of the sperm cell (out of focus in B), all cells depicted did not contain a cytoplasmic droplet as checked by phase-contrast microscopy.