Calcium competes with zinc for a channel mechanism on the brush border membrane of piglet intestine

Interactions between Ca+2 and Zn+2 at the intestinal brush border membrane occur via unclear mechanisms. We hypothesized that Zn+2 and Gait are transp orted across the brush border membrane via a multidivalent metal channel. U sing brush border membrane vesicles (BBMV) prepared from intestines of 8 so w-fed piglets, we sought to determine whether Ca+2 competes with Zn+2 for u ptake. Extravesicular Zn+2 was removed with ethylenediamine-tetraacetic aci d. Time curves of Zn+2 and Ca+2 uptake by BBMV were conducted with increasi ng concentrations of Ca+2 and Zn+2, respectively. Saturation curves compare d kinetic parameters of Zn+2 uptake with and without Ca+2. In addition, Zn2 uptake was measured in the presence of various classical Ca+2 channel mod ulators. Over 20 min, a 0.4X concentration of Zn+2 lowered Ca+2 uptake by v esicles, whereas a 30X concentration of Ca+2 was necessary to lower Zn+2 up take. These data suggest that Ca+2 has lower affinity than Zn+2 for a brush border membrane transport protein. Kinetic parameters showed higher K-m va lues with 4 or 15 mM Ca+2 but unchanged J(max), suggesting competitive inhi bition. The Ca+2 channel blocking agents, La+3, Ba+2, verapamil, and diltia zem, inhibited Zn+2 uptake, whereas calcitriol, trans 1,2 cyclohexanediol, cis/trans 1,3 cyclohexanediol, and the L-type Ca+2 channel agonist, Bay K86 44, induced Zn+2 uptake. These data were consistent with competition for a common transport mechanism on the brush border membrane, possibly a novel m ultimetal channel. (C) 2001 Elsevier Science Inc. All rights reserved.