Characterization of anionic amino acid transport systems in mouse mammary gland

Abstract

<img src='http://www.niscair.res.in/jinfo/small.gif' border=0>-glutamate was transported into mammary tissue via Na⁺-dependent system X_AG- that strongly interacted with both <img src='http://www.niscair.res.in/jinfo/smaller.gif' border=0> and <img src='http://www.niscair.res.in/jinfo/small.gif' border=0>-isomers of aspartate but only with <img src='http://www.niscair.res.in/jinfo/small.gif' border=0>-isomer of glutamate. Replacement of Cl ̅ by gluconate from the extracellular medium did not affect the uptake of <img src='http://www.niscair.res.in/jinfo/small.gif' border=0>-glutamate. Although neutral amino acids weakly inhibited the uptake of <img src='http://www.niscair.res.in/jinfo/small.gif' border=0>-glutamate, there was no evidence for the heterogeneity of anionic amino acid transport system. The X_AG- system was inhibited by sulfhydryl group blocking reagent <i>N</i>-ethylmalemide. Low <i>p</i>H (6) partially inhibited the uptake by <img src='http://www.niscair.res.in/jinfo/small.gif' border=0>-glutamate by mammary

tissue. Prior loading of mammary tissue with <img src='http://www.niscair.res.in/jinfo/small.gif' border=0>-glutamate slightly down regulated its uptake. Culturing pregnant mouse mammary tissue explants <i>in vitro </i>in the presence of lactogenic hormones (insulin plus cortisol plus prolactin) did not affect appreciably the uptake of <img src='http://www.niscair.res.in/jinfo/small.gif' border=0>-glutamate.