Characteristics ofα–aminoisobutyric acid transport by lactating rat mammary gland

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Abstract
Summary: The transport of α-aminoisobutyric acid (AIB) by lactating rat mammary tissue has been examined. AIB uptake by mammary tissue was via both Na+-dependent and Na+-independent pathways. AIB uptake via the Na+-dependent pathway was inhibited by (methylamino)isobutyric acid (MeAIB) whereas AIB uptake via the Na+-independent pathway was blocked by 2-aminobicyclo[2, 2, 1]-heptane-2-carboxylic acid (BCH). A small fraction of AIB influx persisted in the presence of both MeAIB and BCH. The Na+-independent moiety of AIB uptake was strongly inhibited by phenylalanine, tryptophan, leucine, isoleucine and methionine. AIB efflux from mammary tissue slices was found to be both Na+-dependent and Na+-independent. Trans-stimulation of AIB efflux by other amino acids was not observed; in contrast, external phenylalanine, tryptophan and leucine inhibited AIB efflux. The results are largely consistent with the presence of systems A and L in lactating rat mammary tissue. However, the Na+-independent fraction of AIB transport may represent transport via a tissue specific form of system L.