How many zinc transporter families are there?

There are two major zinc transporter families in eukaryotes – the ZnT (SLC30) family and the SLC39 (ZIP) family. The two zinc transporter families function in opposite directions to maintain cellular zinc homeostasis. When cytoplasmic zinc concentrations are elevated, SLC30 family lowers zinc levels by exporting zinc out to the extracellular space or locking the excess cytoplasmic zinc into intracellular compartments. When cytoplasmic zinc concentrations are depleted, the SLC39 family increases zinc levels by drawing zinc into the cytoplasm.