[Isoform 1]: Electroneutral proton-coupled antiporter concentrating zinc ions into a variety of intracellular organelles including endosomes, zymogen granules and mitochondria. Thereby, plays a crucial role in cellular zinc homeostasis to confer upon cells protection against its potential cytotoxicity (PubMed:17065149, PubMed:21289295, PubMed:22733820, PubMed:25657003, PubMed:25808614, PubMed:30893306). Regulates the zinc concentration of milk, through the transport of zinc ions into secretory vesicles of mammary cells (PubMed:19496757). By concentrating zinc ions into lysosomes participates to lysosomal-mediated cell death during early mammary gland involution (PubMed:25808614). {ECO:0000269|PubMed:17065149, ECO:0000269|PubMed:19496757, ECO:0000269|PubMed:21289295, ECO:0000269|PubMed:22733820, ECO:0000269|PubMed:25657003, ECO:0000269|PubMed:25808614, ECO:0000269|PubMed:30893306}. [Isoform 2]: Electroneutral proton-coupled antiporter mediating the efflux of zinc ions through the plasma membrane. . This is the function of SLC30A2 (solute carrier family 30 member 2, Ensembl gene identifier ENSG00000158014).