Characterization of Zn2+ transport in Madin-Darby canine kidney cells

The aim of this study was to characterize the mechanism implicated in Zn2+ transport in MDCK cells. Trace elements such as Zn2+, Cd2+ or Cu2+ induced MDCK cell depolarization at the micromolar level as demonstrated by bis-oxonol fluorescence and whole-cell patch experiments. This depolarization was inhibited by La3+ and Gd3+ and was not related to the activation of Na+ or Cl- channels. Uptake of Zn-65 was assessed under initial rate conditions. The kinetic parameters obtained at 37 degreesC were a K-m of 18.9 muM and a V-max of 0.48 mnol min(-1) (mg protein(-1)). Intracellular pH measurements using BCECF probe demonstrated that Zn2+ transport induced a cytoplasmic acidification. The cytoplasmic acidification resulting from Zn2+ uptake activated Na+/H+ antiporter, which allowed for the recycling of protons. These data suggest that Zn2+ enters MDCK cells through a proton-coupled metal-ion transporter, the characteristics of which are slightly different from those described for the metal transporter DCT1. This mechanism could be in part responsible of the metal transport evidenced in the distal parts of the renal tubule. (C) 2003 Elsevier Science B.V. All rights reserved.