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 Ca+2 are transported across the brush border membrane via a multidivalent metal channel. Using brush border membrane vesicles (BBMV) prepared from intestines of 8 sow-fed piglets, we sought to determine whether Ca+2 competes with Zn+2 for uptake. Extravesicular Zn+2 was removed with ethylenediamine-tetraacetic acid. Time curves of Zn+2 and Ca+2 uptake by BBMV were conducted with increasing concentrations of Ca+2 and Zn+2, respectively. Saturation curves compared kinetic parameters of Zn+2 uptake with and without Ca+2. In addition, Zn+2 uptake was measured in the presence of various classical Ca+2 channel modulators. Over 20 min, a 0.4× concentration of Zn+2 lowered Ca+2 uptake by vesicles, whereas a 30× concentration of Ca+2 was necessary to lower Zn+2 uptake. These data suggest that Ca+2 has lower affinity than Zn+2 for a brush border membrane transport protein. Kinetic parameters showed higher Km values with 4 or 15 mM Ca+2 but unchanged Jmax, suggesting competitive inhibition. The Ca+2 channel blocking agents, La+3, Ba+2, verapamil, and diltiazem, inhibited Zn+2 uptake, whereas calcitriol, trans 1,2 cyclohexanediol, cis/trans 1,3 cyclohexanediol, and the L-type Ca+2 channel agonist, Bay K8644, induced Zn+2 uptake. These data were consistent with competition for a common transport mechanism on the brush border membrane, possibly a novel multimetal channel. © 2001 Elsevier Science Inc. All rights reserved.