In spite of its importance as an environmental health problem, relatively little is known about the specific cellular and biochemical mechanisms by which cadmium produces its many effects. The long-term objective of this project is to identify some of these mechanisms. Reports in the literature suggest that some of the toxic effects of cadmium in vivo may result from the disruption of the junctions between cells in various epithelial or endothelial surfaces. To examine this possibility in more detail, the investigators have been studying the effects of cadmium on cell-cell junctions in the established porcine renal epiethelial cell line, LLC-PK1. Results of preliminary studies have shown that cadmium (as CdCl2) has specific damaging effects on the adhering and occluding junctions between LLC-PK1 cells and that these effects are antagonized by excess Ca2+. The work described in this proposal is a direct extension of these preliminary studies and is aimed at resolving the key issues. The first is to determine whether or not Cd2+ that is bound to metallothionein can disrupt junctions between LLC-PK1 cells in the same manner as Cd2+ itself. This is an important issue because most of the circulating Cd2+ in vivo is bound to metallothionein or similar proteins, and there is evidence to suggest that Cd-metallothionein conjugates may be directly responsible for some of the toxic effects of Cd2+ in vivo. The second issue is to determine whether or not Cd2+ produces its junctional effects by acting on E-cadherin, a Ca2+ binding glycoprotein that plays a key role in Ca2+ dependent cell adhesion mechanisms. These issues will be addressed by using a multidisciplinary approach that includes morphologic, biophysical and biochemical techniques.