The ZnTs are a growing family of proteins involved in lowering or sequestration of cellular zinc. Using fluorescent measurements of zinc transport we have addressed the mechanism of action of the most ubiquitously expressed member of this family, ZnT-1. This protein has been shown to lower levels of intracellular zinc though the mechanism has remained elusive. The rate of zinc efflux in HEK293 cells expressing ZnT-1 was not accelerated in comparison to control cells, suggesting that ZnT-1 may be involved in regulating influx rather than efflux of zinc. Co-expression of the L-type calcium channel, a major route for zinc influx, and ZnT-1 resulted in a 3-fold reduction in the rate of zinc influx in HEK293 and PC-12 cells, indicating that ZnT-1 modulates zinc permeation through this channel. Immunoblot analysis indicates that ZnT-1 expression does not modulate LTCC expression. Our findings therefore indicate that ZnT-1 modulates the permeation of cations through LTCC, thereby, regulating cation homeostasis through this pathway. Furthermore, ZnT-1 may play a role in cellular ion homeostasis and thereby confer protection against pathophysiological events linked to cellular Ca2+ or Zn2+ permeation and cell death. (C) 2004 Elsevier Inc. All rights reserved.