ZnT1 is a neuronal Zn/Ca exchanger.

Zinc transporter 1 (ZnT1; SLC30A1) is present in the neuronal plasma membrane, critically modulating NMDA receptor function and Zn neurotoxicity. The mechanism mediating Zn transport by ZnT1, however, has remained elusive. Here, we investigated ZnT1-dependent Zn transport by measuring intracellular changes of this ion using the fluorescent indicator FluoZin-3. In primary mouse cortical neurons, which express ZnT1, transient addition of extracellular Zn triggered a rise in cytosolic Zn, followed by its removal. Knockdown of ZnT1 by adeno associated viral (AAV)-short hairpin RNA (shZnT1) markedly increased rates of Zn rise, and decreased rates of its removal, suggesting that ZnT1 is a primary route for Zn efflux in neurons. Although Zn transport by other members of the SLC30A family is dependent on pH gradients across cellular membranes, altered H gradients were not coupled to ZnT1-dependent transport. Removal of cytoplasmic Zn, against a large inward gradient during the initial loading phase, suggests that Zn efflux requires a large driving force. We therefore asked if Ca gradients across the membrane can facilitate Zn efflux. Elimination of extracellular Ca abolished Zn efflux, while increased extracellular Ca levels enhanced Zn efflux. Intracellular Ca rises, measured in GCaMP6 expressing neurons, closely paralleled cytoplasmic Zn removal. Taken together, these results strongly suggest that ZnT1 functions as a Zn/Ca exchanger, thereby regulating the transport of two ions of fundamental importance in neuronal signaling.