Localisation and function of voltage-dependent anion channels (VDAC) in bovine spermatozoa

Sperm motility, regulation of cell volume, sperm capacitation, acrosome reaction and tight binding of spermatozoa to the zona pellucida are crucial events in the process of fertilisation. Voltage-dependent anion channels (VDAC) are highly conserved pore-forming proteins implicated in apoptosis, metabolite transport between mitochondria and cytosol, energy metabolism, and cell volume regulation in somatic cells. Several studies have demonstrated the presence of VDAC in cell compartments other than mitochondria. In previous studies using immunofluorescence, we were able to localise VDAC2 and VDAC3 in outer dense fibres of the bovine sperm flagellum. Furthermore, we described the presence of VDAC2 in the head of bovine sperm. In the present study, we confirm the localisation of VDAC2 in the acrosomal region of bovine spermatozoa using immunoelectron microscopy. After incubation with anti-VDAC antibodies raised against each VDAC isoform, bovine spermatozoa showed an increased loss of the acrosomal cap, noticeable changes in the surface of the head, coiled tails and an increased cell volume. The incubation of bovine spermatozoa with anti-VDAC antibodies might lead to alteration of the intracellular ion concentration that causes changes in the cell volume, followed by destabilization of the cytoskeleton and, finally, to loss of the acrosomal cap.