Effect of seminal plasma zinc–binding proteins on motility and membrane integrity of canine spermatozoa stored at 5°C

Sperm surface binding sites for non-zinc-binding proteins (nZnBPs) and zinc-binding proteins (ZnBPs) were studied by the fluorescence technique with biotin-labelled proteins. The nZnBPs binding pattern was unspecific, no characteristic sites on plasmalemma were found. ZnBPs were attached mainly to the acrosomal region of sperm head and to the sperm flagellum. ZnBPs added to the incubation mixture of the canine spermatozoa allowed the preservation of higher values for total motility, progressive motility, curvilinear line velocity, straight line velocity, and beat cross frequency (P < 0.05), both at time 0 and after 1 h incubation at 5ºC. The addition of nZnBPs to the incubation mixture caused only weak positive effects when compared with control sample (PBS). A higher percentage of canine-ejaculated spermatozoa with intact membranes were observed when ejaculate was incubated with ZnBPs in comparison to control sample stored with PBS (P < 0.05) or nZnBPs (P < 0.05). Spermatozoa diluted with ZnBPs and nZnBPs exhibited a higher percentage of cells with active mitochondria when compared with control, both at time 0 and after 1 h; however, no statistical differences were observed. Our results emphasise the role of seminal plasma protein in securing the correct quantity and availability of zinc ions as a component regulating the motility of canine spermatozoa. The protective effect of ZnBPs against the cooling effect may be due to their ability of preventing sperm membrane damage.