Cellular localization of polyamines: cytochemical and ultrastructural methods providing new clues to polyamine...

Polyamine binding sites have been localized in ram spermatozoa using biochemical and cytochemical tools. Incubating the cells with 14C-spermine and determining its distribution after sonication and differential centrifugation, revealed that 60% of the radioactive spermine was localized in the head, 21.5% in the tail and about 9% in the plasma membrane. A polyamine specific cytochemical staining by the formaldehyde-fluorescamine method, revealed that most of the polyamines were localized in the midpiece, where the cell mitochondria are located, and in the acrosome region. Two additional studies used electron microscopy, employing polycationic colloidal gold and spermine-ferritin as cytochemical markers. The most sensitive and specific method was the staining of the cells with ferritin-spermine whose synthesis is described in this study. The outer membrane was the preferential site for spermine binding which was densely distributed in a highly orderly pattern. There was a sparse distribution of spermine binding sites on the plasma membrane surrounding the acrosome and none on the post acrosomal region. The role of spermine in the acrosome reaction and Ca2+ fluxes in sperm cells is discussed.