A STUDY OF CADMIUM TRANSPORT PATHWAYS USING THE CACO-2 CELL MODEL

The purpose of this study was to investigate the mechanism by which ca dmium (Cd2+) crosses the intestinal epithelium using a Caco-2 cell mod el. Experimentation was designed to determine which of several possibl e pathways of transport are operative. These pathways include passive diffusion, transport via a calcium pathway, sulfhydryl-mediated transp ort, and carrier-mediated (active transport and/or facilitated diffusi on) transport, To examine the diffusion pathway the effect of various apical cadmium concentrations on the amount of cadmium transported was tested, The effects of verapamil, calcium, and 1,25(0H)(2) vitamin D- 3 (vit. D-3) on Cd2+ transport were examined to investigate the possib le existence of a calcium transport pathway, N-Ethylmaleimide, a sulfh ydryl group blocker, was used to determine whether Cd2+ transport is s ulfhydryl-mediated. Active transport was evaluated by examining the ef fect of 2,4-dinitrophenol, a metabolic inhibitor, on the transport of Cd2+. These studies indicated that: (1) a portion of the overall trans port of Cd2+ can be attributed to diffusion, (2) stimulation of calciu m binding protein transcription by vit, D-3 enhances Cd2+ transport, a nd (3) the transport process for Cd2+ has both sulfhydryl-mediated and carrier-mediated components. (C) 1997 Academic Press.