Heterogeneity of transport systems for L-glutamine in mouse mammary gland

Abstract

The characteristics of the transport systems of L-glutamine in lactating mouse mammary gland have been studied. L-glutamine uptake was mediated by three Na+-dependent and one Na⁺- independent systems. The 2-(methylamino)isobutyric acid-sensitive component of Na⁺- dependent uptake exhibited the usual characteristics of system A. The other two Na⁺dependent systems, which we have named BCI-dependent and BCI-independent, are the new systems identified. These are broad specificity systems and were discriminated on the basis of inhibition analysis. CI dependency and the effect of preloading mammary tissue with amino acids. While L-aspargine inhibited the uptake of L-glutamine via both these broad

specificity systems. L-homoserine inhibited the uptake of L-glutamine via only BCI-dependent system. The uptake of L-glutamine via the BCI - independent system was upregulated by preloading mammary tissue with L-serine, while BCI-dependent system was unaffected. The Na⁺- independent uptake of L-glutamine was inhibited by 2-aminobicyclo-

(2.2.1 )heptane carboxylic acid and other neutral amino acids, and identified as the system L.