Heterogeneity of cationic amino acid transport systems in mouse mammary gland and their regulation by lactogenic hormones

The mechanism of cationic amino acid transport in lactating mouse mammary gland was investigated. Two Na+-independent systems of arginine transport were discriminated on the basis of their sensitivity to leucine. The leucine-sensitive uptake of arginine (K-m 0.4 mM) was through a broad specificity system that interacted with both cationic and neutral amino acids, and was inhibited by preloading mammary tissue with neutral amino acids. The leucine-insensitive uptaken as identified as the y(+) system (K-m 0.76 mM). Preloading mammary tissue with cationic amino acids increased the uptake of arginine by the y(+) system. Decreasing the FH of the external medium to 6.0 suppressed the y(+) system-mediated uptake by similar to 25%, whereas the broad specificity system remained unaffected. Lactogenic hormones upregulated the y(+) system-mediated uptake of arginine in pregnant mouse mammary tissue cultured in 2 vitro, although the broad specificity system remained unaffected. The y(+) system-mediated. uptake increased 2-fold with insulin alone and 4-fold with the combination of insulin, cortisol and prolactin.