Zinc ion transporter mediating the import of zinc from cytoplasm into synaptic vesicles and participating to cellular zinc ion homeostasis in the brain. Zn(2+)(in) = Zn(2+)(out) Homodimer. Homodimerization is negligible compared to the human protein. It could explain the lower efficiency of zinc transport. Expression is restricted to brain (at protein level). In the brain, most abundant in hippocampus and cerebral cortex. The mRNA is also detected in testis, expression being restricted to germ cells and highest in pachytene spermatocytes and round spermatids. In brain expression is negligible at birth, then increases linearly, reaching a maximum at about 3 weeks postpartum. Homozygous knockout mice lacking Slc30a3 do not display overt phenotype with morphology, body weight, lifespan, fertility, litter size being normal (PubMed:9990090). Zinc ions are eliminated from synaptic vesicles in brain of the knockout mice and the overall levels of zinc in brain is decreased (PubMed:9990090). Belongs to the cation diffusion facilitator (CDF) transporter (TC 2.A.4) family. SLC30A subfamily.